| Tsuyohiko Fujigaya | Last modified date：2024.04.25 |
Professor /
Molecular Information Chemistry /
Department of Applied Chemistry /
Faculty of Engineering
Papers
| 1. | Yuki Motoishi, Chaerin Kim, Naoki Tanaka, Tsuyohiko Fujigaya, Molecular Assembly of Alkylated Fused Expanded Pyridinium for a Highly Conductive Anion-Exchange Membrane, 35, 19, 8030-8038, 2024.04. |
| 2. | Naoki Tanaka, Mei Yamamoto, Itsuki Yamaguchi, Aoi Hamasuna, Emi Honjo, Tsuyohiko Fujigaya, Photolithographic p–n patterning of single-walled carbon nanotube sheets using photobase generators, Journal of Materials Chemistry A, https://doi.org/10.1039/D3TA05067J, 11, 43, 23278-23287, 2023.10. |
| 3. | Yukiko Nagai, Ryo Hamano, Kenta Nakamura, Isabella A. Widjaja, Naoki Tanaka, Minfang Zhang, Takeshi Tanaka, Hiromichi Kataura, Masako Yudasaka, Tsuyohiko Fujigaya, Bright NIR-II fluorescence from biocompatible gel-coated carbon nanotubes for in vivo imaging, Carbon, https://doi.org/10.1016/j.carbon.2023.118728, 218, 31, 118728, 2023.12, [URL]. |
| 4. | Ryo Hamano, Naoki Tanaka, Tsuyohiko Fujigaya, Size exclusion chromatography-based length sorting of single-walled carbon nanotubes stably coated with cross-linked polymer, Materials Advcance, https://doi.org/10.1039/D3MA01069D, 5, 2482-2490, 2024.02, [URL]. |
| 5. | Naoki Tanaka, Itsuki Yamaguchi, Ryohei Yamaguchi, Tsuyohiko Fujigaya, Study of electron doping mechanism in single-walled carbon nanotubes using dimethylbenzimidazole, Faraday Discussions, https://doi.org/10.1039/D3FD00128H, 250, 390-399, 2023.07. |
| 6. | Boda Yu, Tsuyohiko Fujigaya, Tomohiro Shiraki, Wavelength Modulation of Defect Photoluminescence from Locally Functionalized Single-Walled Carbon Nanotubes Using Heterocycle-Substituted Aryldiazonium Salts, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 10.1246/bcsj.20220320, 96, 2, 127-132, 2023.02, Local chemical functionalization of single-walled carbon nanotubes has been developed for defect introduction to pro-duce locally functionalized SWCNTs (lf-SWCNTs). Compared with the original PL of unmodified SWCNTs, lf-SWCNTs exhibit defect photoluminescence (PL) in near -infrared (NIR) regions with higher quantum yields and red-shifted wave-lengths. Recently, using a few chemical functionalization approaches, considerably red-shifted defect PL (E11*- PL, >1250 nm) of lf-SWCNTs was observed in contrast to typical defect PL (E11* PL, 31150 nm), although the E11*- PL wave-length modulation approaches have yet been unexplored. In this study, we synthesized aryldiazonium salts containing heterocycle substituents at the ortho position for the lf-SWCNT synthesis. The resultant lf-SWCNTs selectively emitted E11* -PL and its wavelength variation was observed by modifying the heterocycle structures. Additionally, wavelength switching of E11*- PL was observed through pH variations, in which the protonation/deprotonation of the ortho-pyridine in the lf-SWCNTs induced large spectral shifts in E11*- PL compared to the observed shifts in earlier para-substituent design sys-tems employing E11* PL. The developed E11*- PL wavelength modulation method based on the functionalized molecule de-signs for the lf-SWCNT synthesis would provide novel NIR PL nanomaterials relevant to advanced bio/medical and telecom application fields.. |
| 7. | Boda Yu, Sadahito Naka, Haruka Aoki, Koichiro Kato, Daiki Yamashita, Shun Fujii, Yuichiro K. Kato, Tsuyohiko Fujigaya, Tomohiro Shiraki, ortho-Substituted Aryldiazonium Design for the Defect Configuration-Controlled Photoluminescent Functionalization of Chiral Single-Walled Carbon Nanotubes, ACS Nano, 10.1021/acsnano.2c09897, 16, 12, 21452-21461, 2022.11, Defect functionalization of single-walled carbon nanotubes (SWCNTs) by chemical modification is a promising strategy for near-infrared photoluminescence (NIR PL) generation at >1000 nm, which has advanced telecom and bio/medical applications. The covalent attachment of molecular reagents generates sp3-carbon defects in the sp2-carbon lattice of SWCNTs with bright red-shifted PL generation. Although the positional difference between proximal sp3-carbon defects, labeled as the defect binding configuration, can dominate NIR PL properties, the defect arrangement chemistry remains unexplored. Here, aryldiazonium reagents with π-conjugated ortho-substituents (phenyl and acetylene groups) were developed to introduce molecular interactions with nanotube sidewalls into the defect-formation chemical reaction. The functionalized chiral SWCNTs selectively emitted single defect PL in the wavelength range of ∼1230-1270 nm for (6,5) tubes, indicating the formation of an atypical binding configuration, different from those exhibited by typical aryl- or alkyl-functionalized chiral tubes emitting ∼1150 nm PL. Moreover, the acetylene-based substituent design enabled PL brightening and a subsequent molecular modification of the doped sites using click chemistry..  |
| 8. | Yasuto Nakagawa, Boda Yu, Yoshiaki Niidome, Keita Hayashi, Aleksandar Staykov, Miku Yamada, Takuya Nakashima, Tsuyoshi Kawai, Tsuyohiko Fujigaya, Tomohiro Shiraki, Photoisomerization of Covalently Attached Diarylethene on Locally Functionalized Single-Walled Carbon Nanotubes for Photoinduced Wavelength Switching of Near-Infrared Photoluminescence, JOURNAL OF PHYSICAL CHEMISTRY C, 10.1021/acs.jpcc.2c02977, 126, 25, 10478-10486, 2022.06, Near-infrared photoluminescence (NIR PL) at regions over 1000 nm is used by advanced optical technologies such as quantum communication and deep tissue bioimaging. We demonstrate that covalent attachment of a diarylethene derivative to single-walled carbon nanotubes (SWCNTs) introduces sp3 carbon defects into the crystalline sp2 carbon networks of SWCNTs through chemical functionalization by which red-shifted and bright NIR PL band at 1142 nm appears. Moreover, its PL wavelength switching is achieved reversibly and repeatedly based on photoisomerization of the diarylethene moieties on the nanotubes. The photoswitching phenomena confirmed by spectroscopic measurements and theoretical calculations reveal that the band gaps for PL change according to the diarylethene isomerization on the nanotubes.. |
| 9. | Yin Kan Phua, Don Terrence Dhammika Weerathunga, Dan Wu, Chaerin Kim, Samindi Madhubha Jayawickrama, Naoki Tanaka, Tsuyohiko Fujigaya, Effect of carbon nanotube-based catalyst layer surface roughness on polymer electrolyte membrane fuel cell performance, Sustainable Energy & Fuels, 10.1039/d2se00857b, 6, 4636-4644, 2022.09, One of the advantages of CNT-based fuel cell catalysts is the formation of free-standing sheets based on filtration. The sheets have a smoother side depending on the filtration direction, which result in the higher performance in the cell.. |
| 10. | Naotoshi Nakashima, Masashi Fukuzawa, Kanako Nishimura, Tsuyohiko Fujigaya, Yuichi Kato, Aleksandar Staykov, Supramolecular Chemistry-Based One-Pot High-Efficiency Separation of Solubilizer-Free Pure Semiconducting Single-Walled Carbon Nanotubes Molecular Strategy and Mechanism, Journal of the American Chemical Society, 10.1021/jacs.0c03994, 142, 27, 11847-11856, 2020.07, Single-walled carbon nanotubes (SWCNTs) have the potential to revolutionize nanoscale electronics and power sources; however, their low purity and high separation cost limit their use in practical applications. Here we present a supramolecular chemistry-based one-pot, less expensive, scalable, and highly efficient separation of a solubilizer/adsorbent-free pure semiconducting SWCNT (sc-SWCNT) using flavin/isoalloxazine analogues with different substituents. On the basis of both experimental and computational simulations (DFT study), we have revealed the molecular requirements of the solubilizers as well as provided a possible mechanism for such a highly efficient selective sc-SWCNT separation. The present sorting method is very simple (one-pot) and gives a promising sc-SWCNT separation methodology. Thus, the study provides insight for the molecular design of an sc-SWCNT solubilizer with a high (n,m)-chiral selectivity, which benefits many areas including semiconducting nanoelectronics, thermoelectric, bio and energy materials, and devices using solubilizer-free very pure sc-SWCNTs.. |
| 11. | Gayoung Kim, Tomohiro Shiraki, Tsuyohiko Fujigaya, Thermal conversion of triazine-based covalent organic frameworks to nitrogen-doped nanoporous carbons and their capacitor performance, Bulletin of the Chemical Society of Japan, 10.1246/BCSJ.20190357, 93, 3, 414-420, 2020.03. |
| 12. | Gayoung Kim, Tomohiro Shiraki, Tsuyohiko Fujigaya, Thermal conversion of triazine-based covalent organic frameworks to nitrogen-doped nanoporous carbons and their capacitor performance, Bulletin of the Chemical Society of Japan, 10.1246/BCSJ.20190357, 93, 3, 414-420, 2020.03, Nanoporous carbons with well-defined pore structures are promising for advanced energy applications. Herein, we fabricate nitrogen-doped porous carbons via direct carbonization of a triazine-based covalent organic framework (TACOF1) that acts as both intrinsic template and carbon/nitrogen source. The carbonized TACOF1 forms porous carbon that has a large surface area (1194 m(2) g(-1)) comprised of high volumes of micro-and meso-pores (0.58 cm(3) g(-1) and 0.44 cm(3) g(-1), respectively) with a narrow size distribution. In addition, nitrogen doping of the graphitic carbons is uniformly achieved. A thermal analysis along with evolved gas investigation reveals that chemical processes, including N-2 gas release and graphitization, vary pore texture formation in the resultant carbons with strong dependence on carbonization temperature. Such structural difference of the carbonized TACOF1 changes electrochemical capacitor behavior. The carbonized TACOF1 synthesized at 800 degrees C is found to show good capacitive performance due to its nitrogen-doped porous structures.. |
| 13. | Ziyi Han, Yuki Motoishi, Tsuyohiko Fujigaya, Alkaline Stability of Anion-Conductive Ionomer Coated on a Carbon Surface, ACS Omega, 10.1021/acsomega.9b01466, 4, 17, 17134-17139, 2019.10, Anion-exchange membrane fuel cells (AEMFCs) are promising technologies that allow the use of nonprecious metals as catalysts because the oxidation reduction reaction at the cathode occurs readily at the high pH of AEMFCs. However, the insufficient chemical stability of the anion-conductive materials in AEMFCs currently limits their development. We studied the chemical stability of the electrolyte in the catalyst layer of AEMFCs containing cationic dimethyl polybenzimidazole (mPBI). Although degradation was observed in an mPBI membrane under alkaline conditions, mPBI coated on a carbon support showed excellent alkaline stability. Because no glass transition temperature was observed for mPBI after coating on the support, the increase of chemical stability was probably associated with the decrease of polymer flexibility.. |
| 14. | Tsuyohiko Fujigaya, Ryota Kanamori, Shinsuke Hirata, Junichi Morita, Masamichi Matsumoto, Masato Eguchi, Il Chan Jang, Tatsumi Ishihara, Naotoshi Nakashima, Effect of nitrogen-containing polymer wrapped around carbon nanotubes for Li–O |
| 15. | Don Terrence Dhammika Weerathunga, Tsuyohiko Fujigaya, The relationship between inherent properties of carbon nanotubes and electrochemical durability of supported-Pt catalysts, Diamond and Related Materials, 10.1016/j.diamond.2019.107459, 97, 2019.08, The durability of polymer electrolyte membrane fuel cells (PEMFCs) is a key issue to be improved, especially for the next generation of PEMFCs that will be required to operate at higher temperatures (> 100 °C). An improvement of the durability of PEMFCs by using carbon nanotubes (CNTs) in place of carbon black as the support material for platinum catalysts is reported. To explore the mechanism for the enhancement of the durability as well as the structural dependency on the type of CNTs, accelerated durability tests are performed using several types of CNTs, which include multi-walled CNTs (MWCNTs) and single-walled CNTs (SWCNTs) loaded with Pt nanoparticles. By comparing the electrochemical surface area degradation and CNT oxidation profiles of their Pt composites, the electrochemical stability of CNTs is revealed to dominate the stability of the Pt. MWCNT having larger diameter with lower degree of side-wall defects offer a better durability than smaller MWCNT and also than SWCNTs. We found that onset temperature in the thermogravimetric analysis and their profiles provide an insight for predicting the durability of their Pt composites, which is useful for selecting of optimum CNTs.. |
| 16. | Samindi Madhubha Jayawickrama, Ziyi Han, Shusaku Kido, Naotoshi Nakashima, Tsuyohiko Fujigaya, Enhanced platinum utilization efficiency of polymer-coated carbon black as an electrocatalyst in polymer electrolyte membrane fuel cells, Electrochimica Acta, 10.1016/j.electacta.2019.05.007, 312, 349-357, 2019.07, The utilization efficiency of platinum (Pt)in polymer electrolyte membrane fuel cells (PEMFCs)needs to be increased to lower the cost of PEMFCs to facilitate their widespread commercialization. Here we developed a novel method to improve the Pt utilization efficiency by coating of polybenzimidazole (PBI)on the surface of the carbon support material; Vulcan. Electrochemical experiments revealed that Pt nanoparticle-loaded PBI-coated Vulcan (denoted as Vulcan/PBI/Pt)electrode possessed a much larger electrochemically active surface area (ECSA)compared with that of Pt nanoparticles directly deposited on Vulcan (Vulcan/Pt). The power density of the cell with Vulcan/PBI/Pt was 1.16 kW g , which was ca. 20% higher than that of the control cell using Vulcan/Pt (0.97 kW g ). We considered that the higher Pt utilization efficiency of Vulcan/PBI/Pt than Vulcan/Pt resulted in such an enhanced ECSA and power density of the PBI-coated system. Two possible reasons were considered for the improvement; namely 1)the polymer layer prevented the loading of Pt nanoparticles into inaccessible micropores of Vulcan and 2)the polymer layer improved the coating homogeneity of Nafion ionomer, and thus improved the proton accessibility for Pt nanoparticles. −1 −1. |
| 17. | Yukiko Nagai, Masako Yudasaka, Hiromichi Kataura, Tsuyohiko Fujigaya, Brighter near-IR emission of single-walled carbon nanotubes modified with a cross-linked polymer coating, Chemical Communications, 10.1039/c9cc02712b, 55, 48, 6854-6857, 2019.05, Photoluminescence (PL) in the near-infrared (NIR) region is an attractive feature of single-walled carbon nanotubes (SWNTs). In this study, we investigated the effect of the chemical structure of the cross-linked polymer coating of polymer-coated SWNTs on the NIR PL emission intensity. We found that brighter NIR emission can be achieved using a more hydrophobic polymer coating.. |
| 18. | Don Terrence Dhammika Weerathunga, Samindi Madhubha Jayawickrama, Yin Kan Phua, Kazutaka Nobori, Tsuyohiko Fujigaya, Effect of polytetrafluoroethylene particles in cathode catalyst layer based on carbon nanotube for polymer electrolyte membrane fuel cells, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20190208, 92, 12, 2038-2042, 2019.01. |
| 19. | Multistep Wavelength, Switching of Near‐infrared Photoluminescence Driven, by Chemical Reactions at Local Dope, Sites of Single‐walled Carbon Nanotubes, Multistep Wavelength Switching of Near‐infrared Photoluminescence Driven by Chemical Reactions at Local Doped Sites of Single‐walled Carbon Nanotubes, Chemistry - A European Journal, 10.1002/chem.201805342, 24, 72, 19162-19165, 2018.12. |
| 20. | Mori, K., Kawaguchi, M., Fujigaya, T., Ohno, J., Ikebe, T., Polymer-coated carbon nanotubes as a molecular heater platform for hyperthermic therapy, Journal of Hard Tissue Biology, 10.2485/jhtb.27.139, 27, 2, 139-146, 2018.04, Carbon nanotubes have been explored as heat-delivery vehicles for thermal ablation of tumors. To use single-walled carbon nanotubes (SWNT) as a “molecular heater” for hyperthermic therapy in cancer treatment, stable dispersibility and smart-targeting potential are necessary. The current study reports the dispersibility and exothermic properties with near-infrared (NIR) exposure for SWNT coated with a copolymer of N-isopropylacrylamide and polyethyleneglycol methacrylate (SWNT/PNIPAM-PEG-hybrid). The SWNT/PNIPAM-PEG hybrid showed stable dispersibility in PBS solution and exothermic potential with NIR exposure. Raman spectroscopy results revealed a hybrid derived Raman peak in mouse liver and spleen lysates for 7 days post-injection that disappeared by 14 days in all tissues (liver, spleen, heart, lung and kidney). These results suggested that the hybrid did not accumulate in mouse organ tissues in the long-term. The SWNT/PNIPAM-PEG hybrid decreased the cell viability (of mouse macrophages) with heat generation by NIR exposure. The results of this study demonstrate that the SWNT/PNIPAM-PEG hybrid is a useful platform for a “molecular heater” applicable to hyperthermic cancer therapy.. |
| 21. | Verma, S., Hamasaki, Y., Kim, C., Huang, W., Lu, S., Jhong, H.-R.M., Gewirth, A.A., Fujigaya, T., Nakashima, N., Kenis, P.J.A., Insights into the Low Overpotential Electroreduction of CO |
| 22. | Shimono, T., Matsuki, M., Yamada, T., Morikawa, M., Yasuda, N., Fujigaya, T., Kimizuka, N., Selective ionic conduction in choline iodide/triiodide solid electrolyte and its application to thermocells, Chemistry Letters, 10.1246/cl.171069, 47, 3, 261-264, 2017.12, A thermocell consisting of choline iodide/triiodide solid electrolyte is developed. Seebeck coefficient of the cell is10.87 mV K11 at ambient temperature, which sign is opposite to that of the aqueous I1/I3 1 cell. The ionic conductivity of I3 1doped choline iodide is higher than that of pure choline iodide by two to four orders of magnitude, reflecting high conductivity of I3 1 in the solid electrolyte. The selective ionic conduction observed in the solid electrolytes provides a novel design principle for the thermoelectric conversion materials.. |
| 23. | Jhong, H.-R.M., Tornow, C.E., Kim, C., Verma, S., Oberst, J.L., Anderson, P.S., Gewirth, A.A., Fujigaya, T., Nakashima, N., Kenis, P.J.A., Gold Nanoparticles on Polymer-Wrapped Carbon Nanotubes: An Efficient and Selective Catalyst for the Electroreduction of CO |
| 24. | Inas H. Hafez, Mohamed R. Berber, Tsuyohiko Fujigaya, Naotoshi Nakashima, High Electronic Conductivity and Air Stability of Ultrasmall Copper-Metal Nanoparticles Supported on Pyridine-Based Polybenzimidazole Carbon Nanotube Composite, CHEMCATCHEM, 10.1002/cctc.201700921, 9, 22, 4282-4286, 2017.11, The development of synthetic methods of copper nanoparticles (Cu-NPs) on conductive supports is very challenging and receives much attention. Here, we describe a novel technique to grow stable and uniform metallic Cu-NPs homogeneously on the surface of pristine multiwalled carbon nanotube (MWNTs) catalyst support physically functionalized with a pyridine-based polybenzimidazole (PyPBI) polymer that acts as a ligand to capture the Cu-NPs. Cu-metal nanoparticles with a particle size of 5.0 +/- 0.5nm were obtained on the surface of MWNTs with homogenous and uniform distribution. The newly prepared Cu-NPs show a remarkably enhanced air stability and electrical conductivity, compared to the current state of the art Cu-NPs, over 20days and 500 potential cycles, respectively, with a limited degradation rate of Cu-metallic state. The PyPBI polymer plays an essential role in the stability of Cu-NPs on the surface of MWNTs through coordination with PyPBI, suppressing the Cu-degradation process, which usually decreases the Cu application efficiency. Accordingly, the prospects of applications of the present Cu-NPs composite are excellent.. |
| 25. | Tsuyohiko Fujigaya, Chiori Saito, Ziyi Han, Naotoshi Nakashima, Ionomer Grafting to Polymer-wrapped Carbon Nanotubes for Polymer Electrolyte Membrane Fuel Cell Electrocatalyst, CHEMISTRY LETTERS, 10.1246/cl.170744, 46, 11, 1660-1663, 2017.09, Polybenzimidazole-wrapped carbon nanotubes (CNTs) is grafted by quaternized 1,4-diazabicyclo[2,2,2] octane (DABCO) and used as a new electrocatalyst for the anion-exchange membrane fuel cells after loading of platinum nanoparticles. Single-cell measurements reveal that the power density of the cell is 58.8 mW cm(-2), higher than that of non-grafted analogue. We found the grafting approach to be a promising strategy to avoid leaching of the water-soluble quaternized ionomer.. |
| 26. | Fujigaya, T., Shi, Y., Yang, J., Li, H., Ito, K., Nakashima, N., A highly efficient and durable carbon nanotube-based anode electrocatalyst for water electrolyzers, Journal of Materials Chemistry A, 10.1039/c7ta01318c, 5, 21, 10584-10590, 2017.04, Iridium (Ir) nanoparticles with a uniform diameter of 1.1 +/- 0.2 nm were homogeneously deposited on multi-walled carbon nanotubes (MWNTs) wrapped by polybenzimidazole (PBI), in which PBI enables efficient anchoring of the Ir nanoparticles. The Ir nanoparticles were electrochemically oxidized to afford Ir oxide (IrOx) and evaluated as an oxygen evolution reaction catalyst by half-cell measurements. The composite was also used as an anode electrocatalyst for proton exchange membrane water electrolyzers (PEMWEs). It was revealed that the IrOx on the PBI-wrapped MWNTs exhibited a very high electrocatalytic mass activity and durability even compared to the other state-of-the-art Ir-based catalysts, while the IrOx deposited on conventional carbon black showed only a poor durability.. |
| 27. | Yang, J., Fujigaya, T., Nakashima, N., Decorating unoxidized-carbon nanotubes with homogeneous Ni-Co spinel nanocrystals show superior performance for oxygen evolution/reduction reactions, Scientific Reports, 10.1038/srep45384, 7, 2017.03, We present a new concept for homogeneous spinel nanocrystal-coating on high crystalline pristine-carbon nanotubes (CNTs) for efficient and durable oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Oxidized CNTs have widely been used to functionalize with metal or metal oxides since the defect sites act as anchoring for metal oxide binding. However, such defects on the tubes cause the decrease in electrical conductivity and stability, leading to lower catalyst performance. In the present study, at first, pristine multi-walled carbon nanotubes (MWNTs) were wrapped by pyridine-based polybenzimidazole (PyPBI) to which uniform NixCo3-xO4 nanocrystals were homogeneously deposited by the solvothermal method without damaging the MWNTs, in which PyPBI acted as efficient anchoring sites for the deposition of spinel oxide nanocrystals with -5 nm size. The obtained catalyst (MWNT-PyPBI-NixCo3-xO4) outperformed most state-of-the-art non-precious metal-based bifunctional catalysts; namely, for OER, the potential at 10 mA cm(-2) and Tafel slope in 1 M KOH solution were 1.54 V vs. RHE and 42 mV dec(-1), respectively. For ORR, the onset and half-wave potentials are 0.918 V and 0.811 V vs. RHE, respectively. Moreover, the MWNT-PyPBI-NixCo3-xO4 demonstrates an excellent durability for both ORR and OER.. |
| 28. | Nakashima, Y., Nakashima, N., Fujigaya, T., Development of air-stable n-type single-walled carbon nanotubes by doping with 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole and their thermoelectric properties, Synthetic Metals, 10.1016/j.synthmet.2016.11.042, 225, 76-80, 2017.03, N-type single-walled carbon nanotubes fabricated by doping of organic dopant, 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole, shows remarkable air-stability for over 90 days under atmospheric environment. Formation of stable complex between cationic dopant and anionic SWCNT is considered as the key to prevent the air oxidation. (C) 2016 Published by Elsevier B.V.. |
| 29. | J. Yang, F. Toshimitsu, Z. Yang, T. Fujigaya, N. Nakashima, Pristine carbon nanotube/iron phthalocyanine hybrids with a well-defined nanostructure show excellent efficiency and durability for the oxygen reduction reaction, JOURNAL OF MATERIALS CHEMISTRY A, 10.1039/c6ta07882f, 5, 3, 1184-1191, 2017.01, Development of non-platinum electrocatalysts with high performance, durability, and scalability for fuel cells and batteries is a strong social demand for a next-generation eco-friendly energy society. Here, we present a pristine multi-walled carbon nanotube/iron phthalocyanine (MWNT/FePc) hybrid catalyst with a well-defined nanostructure for the oxygen reduction reaction (ORR) in alkaline media that meets this demand. By carefully tuning the microstructure of the FePc stack layer deposited on the highly crystallized graphitic surface of a MWNT support, an ultra-high ORR activity as well as excellent durability are obtained. Moreover, a power density of 185 mW cm(-2) at 0.8 V was obtained for a zinc-air battery using this optimized MWNT/FePc cathode at room temperature. Density functional theory-based calculations of such a well-defined nanostructure of MWNT/FePc have suggested that deposition on the bent graphitic surface of MWNTs significantly changes the geometric and electronic structures of FePc that originated from pi-pi interactions, leading to such enhanced electrocatalytic activity and durability.. |
| 30. | 藤ヶ谷 剛彦, Toward the development of highly durable polymer electrolyte fuel cell using carbon nanotube, Journal of Fiber Science and Technology, 73, 213-214, 2017.01. |
| 31. | Zehui Yang, Akiyo Nagashima, Tsuyohiko Fujigaya, Naotoshi Nakashima, Electrocatalyst composed of platinum nanoparticles deposited on doubly polymer-coated carbon nanotubes shows a high CO-tolerance in methanol oxidation reaction, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 10.1016/j.ijhydene.2016.08.198, 41, 42, 19182-19190, 2016.11, High CO-tolerance and durability of anodic fuel cell electrocatalysts is one of the important factors for commercialization of direct methanol fuel cells (DMFCs). In this study, we describe the preparation of an electrocatalyst composed of poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) and poly(vinylphosphonic acid) (PVPA) coated multi-walled carbon nanotubes (MWNTs) on which similar to 3 nm Pt nanoparticles (Pt-NPs) are deposited. The fabricated electrocatalyst shows 1.5-times higher CO tolerance compared to the commercial CB/Pt, which would be due to the wrapping of the CNTs with PVPA by the aid of PyPBI. Meanwhile, the electrocatalyst almost maintains its initial electrochemical surface area (ECSA) and mass activity of the methanol oxidation reaction (MOR) after 10,000 potential cycling in the range of 1-1.5 V vs. RHE. In contrast, the commercial CB/Pt shows almost a 50% loss in its ECSA and mass activity. These results indicate that the durability of the newly fabricated electrocatalyst is quite high and the obtained high CO-tolerance and durability are important for the design of an electrocatalyst for DMFC applications. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.. |
| 32. | Hua Li, Tsuyohiko Fujigaya, Hironori Nakajima, Akiko Inada, Kohei Ito, Optimum structural properties for an anode current collector used in a polymer electrolyte membrane water electrolyzer operated at the boiling point of water, JOURNAL OF POWER SOURCES, 10.1016/j.jpowsour.2016.09.086, 332, 16-23, 2016.11, This study attempts to optimize the properties of the anode current collector of a polymer electrolyte membrane water electrolyzer at high temperatures, particularly at the boiling point of water. Different titanium meshes (4 commercial ones and 4 modified ones) with various properties are experimentally examined by operating a cell with each mesh under different conditions. The average pore diameter, thickness, and contact angle of the anode current collector are controlled in the ranges of 10-35 mu m, 0.2 -0.3 mm, and 0-120 degrees, respectively. These results showed that increasing the temperature from the conventional temperature of 80 degrees C to the boiling point could reduce both the open circuit voltage and the overvoltages to a large extent without notable dehydration of the membrane. These results also showed that decreasing the contact angle and the thickness suppresses the electrolysis overvoltage largely by decreasing the concentration overvoltage. The effect of the average pore diameter was not evident until the temperature reached the boiling point. Using operating conditions of 100 degrees C and 2 A/cm(2), the electrolysis voltage is minimized to 1.69 V with a hydrophilic titanium mesh with an average pore diameter of 21 mu m and a thickness of 0.2 mm. (C) 2016 Elsevier B.V. All rights reserved.. |
| 33. | Nasef, M.M., Fujigaya, T., Abouzari-Lotf, E., Nakashima, N., Electrospinning of poly(vinylpyrrodine) template for formation of ZrO |
| 34. | Wenxin Huang, Naotoshi Nakashima, Tsuyohiko Fujigaya, Solvent-free Fabrication of Carbon Nanotube/Resin Composite for Printable Thermoelectric Device, CHEMISTRY LETTERS, 10.1246/cl.160399, 45, 8, 875-877, 2016.08, We describe the preparation of a printable ink composed of single-walled carbon nanotubes (SWNTs) and a curable diacrylate monomer (R712), as well as its cured films (SWNT/polymer composite), to evaluate the thermoelectric properties including the Seebeck coefficient, electrical conductivity, and thermal conductivity. The anisotropy of the thermal conductivity was especially investigated and in-plane ZT of the SWNT/polymer composite was determined for the first time. Finally, we have succeeded in printing the patterned array on polyimide film using this ink.. |
| 35. | Tsuyohiko Fujigaya, Shinsuke Hirata, Mohamed R. Berber, Naotoshi Nakashima, Improved Durability of Electrocatalyst Based on Coating of Carbon Black with Polybenzimidazole and their Application in Polymer Electrolyte Fuel Cells, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.6b01316, 8, 23, 14494-14502, 2016.06, Improvement of durability of the electrocatalyst has been the key issue to be solved for the practical application of polymer electrolyte membrane fuel cells. One of the promising strategies to improve the durability is to enhance the oxidation stability of the carbon-supporting materials. In this report, we describe in detail the mechanism of the stability improvement of carbon blacks (CBs; Vulcan and Ketjen) by coating with polybenzimidazole (PBI). Nitrogen adsorption experiments reveal that the PBI coating of CBs results in the capping of the gates of the CB-micropores by the PBI. Since the surface of the micropores inside the CBs are inherently highly oxidized, the capping of such pores effectively prevents the penetration of the electrolyte into the pore and works to avoid the further oxidation of interior of the micropore, which is proved by cyclic voltammogram measurements. Above mechanism agrees very well with the dramatic enhancement of the durability of the membrane electrode assembly fabricated using Pt on the PBI-coated CBs as an electrocatalyst compared to the conventional Pt/CB (PBI-non coated) catalyst.. |
| 36. | Hua Li, Akiko Inada, Tsuyohiko Fujigaya, Hironori Nakajima, Kazunari Sasaki, Kohei Ito, Effects of operating conditions on performance of high-temperature polymer electrolyte water electrolyzer, JOURNAL OF POWER SOURCES, 10.1016/j.jpowsour.2016.03.108, 318, 192-199, 2016.06, Effects of operating conditions of a high-temperature polymer electrolyte water electrolyzer (HT-PEWE) on the electrolysis voltage are evaluated, and the optimal conditions for a high performance are revealed. A HT-PEWE unit cell with a 4-cm(2) electrode consisting of Nafion117-based catalyst-coated membrane with IrO2 and Pt/C as the oxygen and hydrogen evolution catalysts is fabricated, and its electrolysis voltage and high-frequency resistance are assessed. The cell temperature and pressure are controlled at 80-130 degrees C and 0.1-0.5 MPa, respectively. It is observed that increasing the temperature at a constant pressure of 0.1 MPa does not increase the ohmic overvoltage of the cell; however, it does increase the concentration overvoltage. It is also found that the increase in the overvoltage resulting from the rise in the temperature can be suppressed by elevating the pressure. When operating the cell at a temperature of 100 degrees C, pressure greater than 0.1 MPa suppresses the overvoltage, and so does pressures greater than 0.3 MPa at 130 degrees C. This behavior suggests that keeping the water in a liquid water phase by increasing the pressure is critical for operating PEWEs at high temperatures. (C) 2016 Elsevier B.V. All rights reserved.. |
| 37. | Syouhei Nishihama, Seitaro Takayama, Kazuharu Yoshizuka, Tsuyohiko Fujigaya, Naotoshi Nakashima, Photo-swing extraction system for the separation of lanthanide using a pyrene group-containing thermosensitive polymer combined with carbon nanotubes, SEPARATION SCIENCE AND TECHNOLOGY, 10.1080/01496395.2016.1147468, 51, 15-16, 2492-2500, 2016.05, A novel photo-swing extraction system for lanthanide separation was developed using a copolymer of acid phosphoxy ethyl methacrylate (Phosmer-M), N-isopropylacrylamide (NIPAM), and (1-pyrene)methyl methacrylate (Phosmer-M/NIPAM/PyMMA). Single-walled carbon nanotubes (CNTs) were successfully dispersed in the Phosmer-M/NIPAM/PyMMA as a result of the - interactions of the pyrene groups. The phase transition of the copolymer was successfully induced via photo-irradiation as a result of heat generation by the CNTs. The extraction of Eu(III) was increased by the photo-irradiation because of changes in volume and hydrophobicity of the copolymer. Separation of the lanthanides was improved by the photo-irradiation, especially for the combination of Eu(III)/Sc(III).. |
| 38. | Mohamed Mahmoud Nasef, Tsuyohiko Fujigaya, Ebrahim Abouzari-Lotf, Naotoshi Nakashima, Zehui Yang, Enhancement of performance of pyridine modified polybenzimidazole fuel cell membranes using zirconium oxide nanoclusters and optimized phosphoric acid doping level, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 10.1016/j.ijhydene.2016.03.022, 41, 16, 6842-6854, 2016.05, Nanocomposite proton conducting membranes incorporating zirconium oxide (ZrO2) nanoclusters into solution cast 2,6-pyridine polybenzimidazole (2,6-Py-PBI) films and doped with phosphoric acid (PA) were prepared. The content of ZrO2 nanoclusters in the membrane matrix was varied from 0 to 10 wt%. The parameters of the acid doping reaction were optimized by the response surface method (RSM). The membrane properties were evaluated by Fourier transform infrared (FTIR), scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), universal mechanical tester and DC impedance. The incorporation of 5 wt% ZrO2 nanoclusters increased the acid doping level and remarkably enhanced the proton conductivity of the membrane. A maximum proton conductivity of 60.0 mS/cm was recorded compared to 21.5 and 12.0 mS/cm for pristine and 10 wt% ZrO2 containing membranes at 150 degrees C and dry condition, respectively. The membrane with 5 wt% ZrO2 also showed the highest performance in a single cell at 120 degrees C under dry conditions. The results suggest that the composite membrane containing 5 wt% ZrO2 nanoclusters has a potential for application in high temperature proton exchange membrane fuel cell application. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.. |
| 39. | Li Hua, Akiko Inada, Tsuyohiko Fujigaya, Hironori NAKAJIMA, Kazunari SASAKI, Kohei Ito, Effects of operating conditions on performance of high-temperature polymer electrolyte water electrolyzer, Journal of Power Sources, doi:10.1016/j.jpowsour.2016.03.108, 318, 192-199, 2016.04. |
| 40. | Yusuke Tsutsumi, Tsuyohiko Fujigaya, Naotoshi Nakashima, Requirement for the Formation of Crosslinked Polymers on Single-walled Carbon Nanotubes Using Vinyl Monomers, CHEMISTRY LETTERS, 10.1246/cl.151086, 45, 3, 274-276, 2016.03, Synthesis of a crosslinked polymer on single-walled carbon nanotubes (SWNTs) is a promising method for functionalization of the SWNTs due to their high coating stability together with their intactness to the SWNTs. We here reveal a requirement for vinyl monomers to form such crosslinked polymers on the SWNTs, which is highly important to generalize this method as well as to develop many polymer-SWNT hybrids with a unique structure and functions.. |
| 41. | Tsuyohiko Fujigaya, Yusuke Saegusa, Shogo Momota, Nobuhide Uda, Naotoshi Nakashima, Interfacial Engineering of Epoxy/Carbon Nanotube by using Reactive Glue for Effective Reinforcement of the Composite, Polymer Journal, 48, 183-188, 2016.02. |
| 42. | Tsuyohiko Fujigaya, ChaeRin Kim, Yuki Hamasaki, Naotoshi Nakashima, Growth and Deposition of Au Nanoclusters on Polymer-wrapped Graphene and Their Oxygen Reduction Activity, SCIENTIFIC REPORTS, 10.1038/srep21314, 6, 2016.02. |
| 43. | Tsuyohiko Fujigaya, Yusuke Saegusa, Shogo Momota, Nobuhide Uda, Naotoshi Nakashima, Interfacial engineering of epoxy/carbon nanotubes using reactive glue for effective reinforcement of the composite, Polymer Journal, 10.1038/pj.2015.98, 48, 2, 183-188, 2016.02, We describe a novel strategy for reinforcing an epoxy resin using carbon nanotubes (CNTs), in which polybenzimidazole (PBI) was used as the glue to enable effective adhesion between the epoxy matrix and the CNT surface. Because PBI strongly interacts with the surfaces of the CNTs and reacts with epoxy matrices to form covalent bonds, the PBI-wrapped CNTs are a promising novel epoxy-CNT hybrid. The PBI-wrapped CNTs (CNT/PBI) exhibited an effective reinforcement of the epoxy resin hybrid, resulting in a higher tensile strength and Young's modulus (that is, +28.1% and +8.8%, respectively) compared with those of the hybrid using oxidized CNTs in place of PBI-wrapped CNTs (+18.6% and -4.8% reinforcement for tensile strength and Young's modulus, respectively). Scanning electron microscopy measurements of the fracture surfaces of the CNT/PBI-epoxy hybrid revealed that only very short CNTs were observed for the CNT/PBI-epoxy hybrid due to effective load transfer resulting from the formation of covalent bonds between the PBI on the CNTs and the epoxy resin, which is in contrast to that observed for oxidized CNT-epoxy, which exhibited long CNTs in the fracture surfaces owing to slippage at the interfaces.. |
| 44. | Tsuyohiko Fujigaya, ChaeRin Kim, Yuki Hamasaki, Naotoshi Nakashima, Growth and Deposition of Au Nanoclusters on Polymer-wrapped Graphene and Their Oxygen Reduction Activity, SCIENTIFIC REPORTS, 10.1038/srep21314, 6, 2016.02, The development of a non-Pt electrocatalyst with a high performance for the oxygen reduction reaction (ORR) is one of the central issues in polymer electrolyte fuel cells science. Au-nanoparticles (Au-NPs) with a diameter of <2 nm are one of the promising substitutes of Pt-NPs; however, it is still a challenge to synthesize such a small-sized Au-NPs with a narrow diameter distribution on a carbon support without using capping agents. We here describe a facile method to deposit uniform Au-NPs (diameter = 1.6 nm and 3.3 nm) on the stacked-graphene (<10 layers) coated with poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] without using any capping agents. The obtained Au-NPs exhibit an excellent ORR activity with the onset potential at -0.11 V and -0.09 V (vs. Ag/AgCl) for 1.6 nm and 3.3 nm, respectively. On the other hand, inhomogeneous Au-NPs with 4.6 nm in average diameter shows the onset potential at -0.15 V (vs. Ag/AgCl).. |
| 45. | Tsuyohiko Fujigaya, Yusuke Saegusa, Shogo Momota, Nobuhide Uda, Naotoshi Nakashima, Interfacial engineering of epoxy/carbon nanotubes using reactive glue for effective reinforcement of the composite, POLYMER JOURNAL, 10.1038/pj.2015.98, 48, 2, 183-188, 2016.02, We describe a novel strategy for reinforcing an epoxy resin using carbon nanotubes (CNTs), in which polybenzimidazole (PBI) was used as the glue to enable effective adhesion between the epoxy matrix and the CNT surface. Because PBI strongly interacts with the surfaces of the CNTs and reacts with epoxy matrices to form covalent bonds, the PBI-wrapped CNTs are a promising novel epoxy-CNT hybrid. The PBI-wrapped CNTs (CNT/PBI) exhibited an effective reinforcement of the epoxy resin hybrid, resulting in a higher tensile strength and Young's modulus (that is, +28.1% and +8.8%, respectively) compared with those of the hybrid using oxidized CNTs in place of PBI-wrapped CNTs (+18.6% and -4.8% reinforcement for tensile strength and Young's modulus, respectively). Scanning electron microscopy measurements of the fracture surfaces of the CNT/PBI-epoxy hybrid revealed that only very short CNTs were observed for the CNT/PBI-epoxy hybrid due to effective load transfer resulting from the formation of covalent bonds between the PBI on the CNTs and the epoxy resin, which is in contrast to that observed for oxidized CNT-epoxy, which exhibited long CNTs in the fracture surfaces owing to slippage at the interfaces.. |
| 46. | Zehui Yang, Tsuyohiko Fujigaya, Naotoshi Nakashima, NaOH-Aided Platinum Nanoparticle Size Regulation on Polybenzimidazole-Wrapped Carbon Nanotubes for Use as Non-Humidified Polymer Electrolyte Fuel Cell Catalyst, CHEMCATCHEM, 10.1002/cctc.201501089, 8, 1, 268-275, 2016.01, We describe a method to control the size of platinum nanoparticles (PtNPs) on poly[2,2'-(2,6-pyridine)5,5'-bibenzimidazole] (PyPBI)wrapped pristine multi-walled carbon nanotubes (MWNTs) without changing the loading amount by adding various concentrations of sodium hydroxide (NaOH) to the ethylene glycol aqueous solutions. The Pt-NP sizes decreased from 3.8 +/- 0.4 to 1.7 +/- 0.1 nm with increasing NaOH concentrations. The mass activity of the oxygen reduction reaction was 224 mAmg(Pt)(-1) for the electrocatalyst with 3 nm Pt-NPs, in which the power density reached 350 mWcm(-2), which was 1.4 times higher than that of the electrocatalyst synthesized without NaOH (250 mWcm(-2)) at 120 degrees C and without any extra humidification. The electrocatalyst synthesized from a small amount of additional NaOH (0.5 mm) in the starting solution shows an enhanced performance and similar Pt stability. More importantly, the Pt-NP size showed no effect on the Pt stability owing to the use of the PyPBI.. |
| 47. | Zehui Yang, Tsuyohiko Fujigaya, Naotoshi Nakashima, Homogeneous coating of ionomer on electrocatalyst assisted by polybenzimidazole as an adhesive layer and its effect on fuel cell performance, JOURNAL OF POWER SOURCES, 10.1016/j.jpowsour.2015.09.069, 300, 175-181, 2015.12, The fabrication of homogeneous ionomer distribution in fuel cell catalyst layers is necessary and important to improve the platinum utilization as well as the power density. Here, we focus on the effect of poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) wrapped on multi-walled carbon nanotubes (MWNTs) for anchoring Nafion ionomer to the electrocatalyst, in which PyPBI functions as the binding sites for platinum nanoparticles (Pt-NPs) used as a catalyst. Based on the result using a control composite without having PyPBI, a strong interaction of the Nation onto the PyPBI layer is recognized. Importantly, we find that the membrane-electrode assembly (MEA) shows a much higher maximum power density than that of the MEA without PyPBI. A homogeneous coating of Nafion on the electrocatalyst using the PyPBI forms a long-range network of the ionomer, leading to an improved Pt-NP utilization efficiency as well as an enhanced power density of the MEA. (C) 2015 Elsevier B.V. All rights reserved.. |
| 48. | Yusuke Tsutsumi, Tsuyohiko Fujigaya, Naotoshi Nakashima, Size reduction of 3D-polymer-coated single-walled carbon nanotubes by ultracentrifugation, NANOSCALE, 10.1039/c5nr05066a, 7, 46, 19534-19539, 2015.12, We describe a novel single-walled carbon nanotube (SWNT) cutting method without introducing any structural defects on the tubes; namely, the finding that simple ultracentrifugation at 600 000g for the SWNTs coated with a cross-linked polymer formed by poly(N-isopropylacrylamide) (PNIPAM) or the polyethylene glycol-carrying PNIPAM copolymer provides shortened (<200 nm) SWNTs, which was revealed by dynamic light scattering (DLS) and atomic force microscopy (AFM) measurements. The Raman and absorption measurements of the obtained SWNTs indicated that the graphitic structure and optical properties, such as characteristic absorption and photoluminescence in the near-IR region of the SWNTs, were almost unchanged even after the cutting. The obtained shortened SWNTs were individually solubilized in water and buffer solution due to the remaining cross-linked polymer structures on the SWNTs. The present method is very simple (only ultracentrifugation) and the yield is very high, which are the advantages in the preparation of many shortened isolated SWNTs with specific properties and functions that are applicable in many fields including bioapplications in vivo, such as imaging, NIR-hyperthermic treatment, photodynamic therapy, etc.. |
| 49. | Yusuke Tsutsumi, Tsuyohiko Fujigaya, Naotoshi Nakashima, Requirement for the Formation of Cross-linked Polymer on Single-walled Carbon Nanotubes Using Vinyl Monomers, Chem. Lett., 45, 3, 274-276, 2015.12. |
| 50. | Mohamed R. Berber, Inas H. Hafez, Tsuyohiko Fujigaya, Naotoshi Nakashima, A highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes, Scientific reports, 10.1038/srep16711, 5, 2015.11, Driven by the demand for the commercialization of fuel cell (FC) technology, we describe the design and fabrication of a highly durable FC electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The fabricated electrocatalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm 2 (at 70 Ëš C, 50% relative humidity using air (cathode)/H 2 (anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5% loss of the initial FC potential and 20% loss of the maximum power density, which were far superior properties compared to those of the membrane electrode assembly prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.. |
| 51. | Mohamed R. Berber, Inas H. Hafez, Tsuyohiko Fujigaya, Naotoshi Nakashima, A highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes, SCIENTIFIC REPORTS, 10.1038/srep16711, 5, 2015.11, Driven by the demand for the commercialization of fuel cell (FC) technology, we describe the design and fabrication of a highly durable FC electrocatalyst based on double-polymer-coated carbon nanotubes for use in polymer electrolyte membrane fuel cells. The fabricated electrocatalyst is composed of Pt-deposited polybenzimidazole-coated carbon nanotubes, which are further coated with Nafion. By using this electrocatalyst, a high FC performance with a power density of 375 mW/cm(2) (at 70 degrees C, 50% relative humidity using air (cathode)/H-2(anode)) was obtained, and a remarkable durability of 500,000 accelerated potential cycles was recorded with only a 5% loss of the initial FC potential and 20% loss of the maximum power density, which were far superior properties compared to those of the membrane electrode assembly prepared using carbon black in place of the carbon nanotubes. The present study indicates that the prepared highly durable fuel cell electrocatalyst is a promising material for the next generation of PEMFCs.. |
| 52. | BERBER MOHAMED, Tsuyohiko Fujigaya, Naotoshi Nakashima, A highly durable fuel cell electrocatalyst based on double-polymer-coated carbon nanotubes, Scientific Reports, 5, 167111, 2015.10. |
| 53. | Zehui Yang, ChaeRin Kim, Shinsuke Hirata, Tsuyohiko Fujigaya, Naotoshi Nakashima, Facile Enhancement in CO-Tolerance of a Polymer-Coated Pt Electrocatalyst Supported on Carbon Black: Comparison between Vulcan and Ketjenblack, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.5b03371, 7, 29, 15885-15891, 2015.07. |
| 54. | Zehui Yang, Tsuyohiko Fujigaya, Naotoshi Nakashima, A phosphoric acid-doped electrocatalyst supported on poly(para-pyridine benzimidazole)-wrapped carbon nanotubes shows a high durability and performance, Journal of Materials Chemistry A, 10.1039/c5ta01650a, 3, 27, 14318-14324, 2015.07, Low fuel cell performance and durability are still the two main obstacles to the commercialization of high-temperature polymer electrolyte fuel cells. Herein, we have prepared a membrane electrode assembly (MEA) composed of a phosphoric acid (PA)-doped platinum electrocatalyst supported on poly[2,2′-(2,5-pyridine)-5,5′-bibenzimidazole] (para-PyPBI)-wrapped multi-walled carbon nanotubes (denoted MWNTs/para-PyPBI-PA/Pt), and PA-doped para-PyPBI as the electrocatalyst and the electrolyte membrane, respectively. The prepared MWNTs/para-PyPBI-PA/Pt showed a higher electrochemical stability against carbon corrosion compared to that of the conventional CB/Pt; namely, the initial electrochemical surface areas (ECSA) after 10=000 start-up/shutdown cycles (1-1.5 V vs. RHE) of these two electrocatalysts decreased by 20% and 47%, respectively. The power density of the MEA using the MWNTs/para-PyPBI-PA/Pt and PA-doped para-PyPBI measured at 120 °C with external humidification reached 414 mW cm-2, which was approximately 2 and 2.5 times those of the non-PA doped electrocatalyst (208 mW cm-2) and conventional CB/Pt (167 mW cm-2). Meanwhile, under non-humidified operation, the mass power density reached 0.92 W mgPt-1, which is very high for high-temperature PEFCs.. |
| 55. | Tomohiro Shiraki, Shoichiro Shindome, Fumiyuki Toshimitsu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Strong main-chain length-dependence for the β-phase formation of oligofluorenes, Polymer Chemistry, 10.1039/c5py00385g, 6, 28, 5103-5109, 2015.07, Poly-/oligofluorenes are promising luminescent materials applicable in organic light emitting diodes, lasers, etc. In particular, the β-phase structure, in which the fluorene main chain adopts a planar conformation with extended conjugation, shows characteristic optical properties. In this study, we have synthesized oligo(9,9′-dioctylfluorenes) whose chain lengths (n) are n = 9, 12, 15, 18, 21, 24 and 27 mers. Interestingly, the β-phase formation of the oligofluorenes is observed remarkably for oligofluorenes with n > 15, which is confirmed by the UV/vis and fluorescence spectroscopy. This study elucidates the structure-property relationship required to design high performance fluorene-based materials. Such a chain-length-dependent optical property provides useful information for utilizing the materials in many applications.. |
| 56. | Zehui Yang, ChaeRin Kim, Shinsuke Hirata, Tsuyohiko Fujigaya, Naotoshi Nakashima, Facile Enhancement in CO-Tolerance of a Polymer-Coated Pt Electrocatalyst Supported on Carbon Black: Comparison between Vulcan and Ketjenblack, ACS APPLIED MATERIALS & INTERFACES, 10.1021/acsami.5b03371, 7, 29, 15885-15891, 2015.07, The CO poisoning and low durability of the anode platinum electrocatalyst in the direct methanol fuel cell (DMFC) are the two crucial obstacles of the wide commercialization of the DMFC. In this study, we synthesized two different electrocatalysts using VulcanXC-72R (VC) and Ketjenblack (KB) as the carbon supporting material for the methanol oxidation reaction (MOR) and long-term durability test, in which the carbon supporting materials were wrapped by poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI) before the platinum deposition and the fabricated electrocatalysts were coated by the poly(vinylphosphonic acid) (PVPA) via the base-acid reaction. We have found that the as-prepared KB/PyPBI/Pt/PVPA shows a higher durability (7% loss in ECSA) under the potential cycling from 1.0 to 1.5 V vs. RHE compared to that of the VC/PyPBI/Pt/PVPA, which showed a 20% loss in ECSA after 10 000 cycle-durability test. Meanwhile, the KB/PyPBI/Pt/PVPA shows a higher CO tolerance before and after the durability test compared to that of the VC/PyPBI/Pt/PVPA, especially under very high methanol concentration (4 M and 8 M); which is close to the practical application of the DMFC. The observed higher CO tolerance is due to the higher amount of the PVPA (14.6 Wt %) in the KB/PyPBI/Pt/PVPA caused by the higher specific surface area of the KB (1232 m(2)/g) compared to the VC (235 m(2)/g).. |
| 57. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 10.1088/1468-6996/16/2/024802, 16, 2, 2015.04, Carbon nanotubes (CNTs) have been recognized as a promising material in a wide range of applications from biotechnology to energy-related devices. However, the poor solubility in aqueous and organic solvents hindered the applications of CNTs. As studies have progressed, the methodology for CNT dispersion was established. In this methodology, the key issue is to covalently or non-covalently functionalize the surfaces of the CNTs with a dispersant. Among the various types of dispersions, polymer wrapping through non-covalent interactions is attractive in terms of the stability and homogeneity of the functionalization. Recently, by taking advantage of their stability, the wrapped-polymers have been utilized to support and/or reinforce the unique functionality of the CNTs, leading to the development of high-performance devices. In this review, various polymer wrapping approaches, together with the applications of the polymer-wrapped CNTs, are summarized.. |
| 58. | Zehui Yang, Tsuyohiko Fujigaya, Naotoshi Nakashima, A phosphoric acid-doped electrocatalyst supported on poly(para-pyridine benzimidazole)- wrapped carbon nanotubes shows a high durability and performance, J. Mater. Chem. A, 5, 12236, 2015.01. |
| 59. | Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Development of n-type cobaltocene-encapsulated carbon nanotubes with remarkable thermoelectric property, SCIENTIFIC REPORTS, 10.1038/srep07951, 5, 2015.01, Direct conversion from heat to electricity is one of the important technologies for a sustainable society since large quantities of energy are wasted as heat. We report the development of a single-walled carbon nanotube (SWNT)-based high conversion efficiency, air-stable and flexible thermoelectric material. We prepared cobaltocene-encapsulated SWNTs (denoted CoCp2@SWNTs) and revealed that the material showed a negative-type (n-type) semiconducting behaviour (Seebeck coefficient: -41.8 mu V K-1 at 320 K). The CoCp2@SWNT film was found to show a high electrical conductivity (43,200 S m(-1) at 320 K) and large power factor (75.4 mu W m(-1) K-2) and the performance was remarkably stable under atmospheric conditions over a wide range of temperatures. The thermoelectric figure of merit (ZT) value of the CoCp2@SWNT film (0.157 at 320 K) was highest among the reported n-type organic thermoelectric materials due to the large power factor and low thermal conductivity (0.15 Wm(-1) K-1). These characteristics of the n-type CoCp2@SWNTs allowed us to fabricate a p-n type thermoelectric device by combination with an empty SWNT-based p-type film. The fabricated device exhibited a highly efficient power generation close to the calculated values even without any air-protective coating due to the high stability of the SWNT-based materials under atmospheric conditions.. |
| 60. | Naoki Imazu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Fabrication of Highly Transparent, Thermally Stable, and Scalable Conductive Films from Double-Walled Carbon Nanotubes, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 10.1246/bcsj.20140277, 88, 1, 217-221, 2015.01, To fabricate transparent conducting films (TCFs) for electronic devices, both a high conductivity and thermal stability are significant issues due to the need for a high temperature annealing process. In this report, we describe the preparation of a highly transparent (94% transmittance), conductive (surface resistivity: 354 Omega sq(-1)) and thermally stable double-walled carbon nanotube (DWCNT) film without adding any chemical doping or rinsing. Such film was obtained by a simple dilution and condensation/filtration process (DC/F). The procedure is quite simple, and thus large scalability is easy.. |
| 61. | ChaeRin Kim, Tsuyohiko Fujigaya, Naotoshi Nakashima, One-pot Synthesis of Gold-Platinum Core-Shell Nanoparticles on Polybenzimidazole-decorated Carbon Nanotubes, CHEMISTRY LETTERS, 10.1246/cl.140663, 43, 11, 1737-1739, 2014.11, Gold (Au) nanoparticles having a Pt-shell layer (Au-Pt) deposited on a conductive support are a promising electro-catalyst for fuel cells, enabling the minimal use of Pt. We describe a facile one-pot method to grow Au-Pt having a 3.8-nm diameter on multiwalled carbon nanotubes (MWNTs) in the absence of a reducing agent, in which polybenzimidazole was used as the binding sites on the MWNTs to load the Au-Pt.. |
| 62. | Tsuyohiko Fujigaya, Junichi Morita, Naotoshi Nakashima, Grooves of Bundled Single-Walled Carbon Nanotubes Dramatically Enhance the Activity of the Oxygen Reduction Reaction, CHEMCATCHEM, 10.1002/cctc.201402565, 6, 11, 3169-3173, 2014.11, Nitrogen-doped graphitic structures (N-GSs) are promising and cheap catalyst candidates for the oxygen reduction reaction (ORR). In this paper, we describe, first, the synthesis of single-walled carbon nanotubes (SWNTs) coated by a N-GS (SWNT/N-GS) and, second, the dramatic enhancement in the activity of the ORR by using this catalyst relative to that observed for the analogue composite composed of multiwalled carbon nanotubes (MWNTs) coated by a N-GS (i.e., MWNT/N-GS). Scanning electron microscopy and gas-adsorption experiments revealed that the SWNT/N-GS formed a bundled structure and that superior gas adsorption behavior originated from this groove structure. It is assumed that the grooves of the bundled SWNT/N-GS dramatically enhance the activity of the ORR owing to superior O-2 adsorption on the grooves.. |
| 63. | Takao Sada, Tsuyohiko Fujigaya, Naotoshi Nakashima, Layer-by-layer Assembly of Trivalent Metal Cation and Anionic Polymer in Nanoporous Anodic Aluminum Oxide with 35 nm Pore, CHEMISTRY LETTERS, 10.1246/cl.140489, 43, 9, 1478-1480, 2014.09, The successful layer-by-layer assembly formation using a polyanion and trivalent ion, such as Fe3+, on the surfaces of the nanopores in an anodic aluminum oxide membrane with a pore diameter of 35 am is demonstrated.. |
| 64. | JongTae Yoo, SuHyun Lee, Chang Kee Lee, ChaeRin Kim, Tsuyohiko Fujigaya, Hyun Jin Park, Naotoshi Nakashima, Jin Kie Shim, Homogeneous decoration of zeolitic imidazolate framework-8 (ZIF-8) with core-shell structures on carbon nanotubes, RSC ADVANCES, 10.1039/c4ra06792d, 4, 91, 49614-49619, 2014.09, Considerable attention has focused on the combination of carbon nanotubes (CNTs) and metal-organic frameworks (MOFs) since both nanomaterials have outstanding properties. We describe a method for the homogeneous decoration of a MOF (ZIF-8 was chosen) onto the surfaces of CNTs dispersed by polyvinylpyrrolidones (PVPs) in methanol, which was revealed by a scanning electron microscopic study. The homogeneous coating of the MOF on the CNTs, and nanostructures of the CNT-MOF were controlled by simply changing the concentrations of the MOFs. Furthermore, this method was also applicable to graphene and graphene oxide (GO). CO2 uptakes of the CNT-MOF and graphene-MOF were significantly improved as compared to the nonhomogeneous composites synthesized without the PVP functionalization, and a good reproducibility of the CO2 adsorption was confirmed by the cycling test.. |
| 65. | Inas H. Hafez, Mohamed R. Berber, Tsuyohiko Fujigaya, Naotoshi Nakashima, Enhancement of Platinum Mass Activity on the Surface of Polymer-wrapped Carbon Nanotube-Based Fuel Cell Electrocatalysts, SCIENTIFIC REPORTS, 10.1038/srep06295, 4, 2014.09, Cost reduction and improved durability are the two major targets for accelerating the commercialization of polymer electrolyte membrane fuel cells (PEFCs). To achieve these goals, the development of a novel method to fabricate platinum (Pt)-based electrocatalysts with a high mass activity, deposited on durable conductive support materials, is necessary. In this study, we describe a facile approach to grow homogeneously dispersed Pt nanoparticles (Pt) with a narrow diameter distribution in a highly controllable fashion on polymer-wrapped carbon nanotubes (CNTs). A PEFC cell employing a composite with the smallest Pt nanoparticle size (2.3 nm diameter) exhibited a similar to 8 times higher mass activity compared to a cell containing Pt with a 3.7 nm diameter. This is the first example of the diamter control of Pt on polymer-wrapped carbon supporting materials, and the study opens the door for the development of a future-generation of PEFCs using a minimal amount of Pt.. |
| 66. | BERBER MOHAMED, Tsuyohiko Fujigaya, Naotoshi Nakashima, Durability Analysis of Polymer-coated Pristine Carbon Nanotube-based Fuel Cell Electrocatalyst at Non-humidified Conditions, Journal of Materials Chemistry A , 2, 44, 19053-19059, 2014.09. |
| 67. | Mohamed R. Berber, Inas H. Hafez, Tsuyohiko Fujigaya, Naotoshi Nakashima, Durability analysis of polymer-coated pristine carbon nanotube-based fuel cell electrocatalysts under non-humidified conditions, JOURNAL OF MATERIALS CHEMISTRY A, 10.1039/c4ta03956d, 2, 44, 19053-19059, 2014.09, A polymer electrolyte fuel cell (PEFC) that shows high durability at elevated temperature and under non-humidified conditions is strongly demanded for the next generation PEFCs. Here we show the importance of using pristine carbon nanotubes (CNTs) as catalyst supports for fuel cell (FC) durability. For that purpose, two different membrane electrode assemblies (MEAs) using pristine CNTs and commercial carbon black (CB) as carbon supports were coated by polybenzimidazole on which platinum (Pt) nanoparticles were deposited. Notably, the CNT-based MEA exhibited similar to 4 times higher durability compared to the CB-based MEA. The ex situ monitoring of the fabricated electrocatalysts before and after the durability testing based on transmission electron microscopy and X-ray diffraction measurements revealed higher structural stability of the CNTs compared to the CB in their MEAs. The pristine structure of the CNTs has been revealed to be very important for the high PEFC durability. This is the first report that shows the durability of the pristine CNT-based PEFC at high operating temperature and under non-humidified conditions, which are the targets of the next generation PEFCs with very high performance.. |
| 68. | Takao Sada, Tsuyohiko Fujigaya, Naotoshi Nakashima, Manipulation of cell membrane using carbon nanotube scaffold as a photoresponsive stimuli generator, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 10.1088/1468-6996/15/4/045002, 15, 4, 2014.08, We describe, for the first time, the perforation of the cell membrane in the targeted single cell based on the nanosecond pulsed near-infrared (NIR) laser irradiation of a thin film of carbon nanotubes that act as an effective photon absorber as well as stimuli generator. When the power of NIR laser is over 17.5 mu J/pulse, the cell membrane after irradiation is irreversibly disrupted and results in cell death. In sharp contrast, the perforation of the cell membrane occurs at suitable laser power (similar to 15 mu J/pulse) without involving cell termination.. |
| 69. | Takao Sada, Tsuyohiko Fujigaya, Naotoshi Nakashima, Design and fabrication of Ni nanowires having periodically hollow nanostructures, NANOSCALE, 10.1039/c4nr02625j, 6, 19, 11484-11488, 2014.08, We propose a concept for the design and fabrication of metal nanowires having periodically hollow nanostructures inside the pores of an anodic aluminum oxide (AAO) membrane using a sacrificial metal. In this study, nickel (Ni) and silver (Ag) were used as the base metal and the sacrificial metal, respectively. Alternating an applied potential between 0.4 and 1.0 V provided alternatively deposited Ni and Ag segments in a Ni-Ag 'barcode' nanowire with a diameter of 18 or 35 nm. After etching away the Ag segments, we fabricated Ni nanowires with nanopores of 12 +/- 5.3 nm. Such nanostructure formation is explained by the formation of a Ni shell layer over the surface of the Ag segments due to the strong affinity of Ni2+ for the interior surfaces of AAO. The Ni shell layer allows the Ni segments to remain even after dissolution of the Ag segments. Because the electroplating conditions can be easily controlled, we could carefully adjust the size and pitch of the periodically hollow nanospaces. We also describe a method for the fabrication of Ni nanorods by forming an Ag shell instead of a Ni shell on the Ni-Ag barcode nanowire, in which the interior of the AAO surfaces was modified with a compound bearing a thiol group prior to electroplating.. |
| 70. | A. Nagashima, T. Fujigaya, N. Nakashima, Effect of Nanostructure of the Electrocatalyst Based on Carbon Nanotube for the Activation Overpotential for PEFC, POLYMER ELECTROLYTE FUEL CELLS 14, 10.1149/06403.0151ecst, 64, 3, 151-157, 2014.08, Polymer electrolyte fuel cell (PEFC) using liquid phosphoric acid (PA) as polymer electrolyte membrane has poor durability, due to leaching of PA from the membrane, which causes the deterioration of PEFC performance during long-term operation. To overcome this issue, poly(vinylphosphonic acid) (PVPA) was used for electrolyte instead of PA. Although this PEFC showed high durability, this catalyst had large overpotential in the area of low current density, probably due to the poisoning of Pt by PVPA coating. In this study, we explored the new preparation method to avoid the Pt poisoning and investigated the catalytic performance by electrochemical techniques.. |
| 71. | T. Fujigaya, M. R. Berber, N. Nakashima, Design of Highly Durable Electrocatalyst for High-Temperature Polymer Electrolyte Fuel Cell, POLYMER ELECTROLYTE FUEL CELLS 14, 10.1149/06403.0159ecst, 64, 3, 159-169, 2014.08, We describe a polymer electrolyte fuel cell (PMFC) with an extremely high durability (single cell test: >400,000 cycling) together with a high power density (252 mW/cm(2)) at high temperature (120 degrees C) under a non-humid atmosphere. Such a high performance PMFC development opens the door for the next-generation PEFC for "real world" use. This is achieved by using a membrane electrode assembly (MEA) with poly(vinylphosphonic acid)-doped poly[2,2'-(2,6-pyridine)-5,5'-bibenzimidazole] (PyPBI)-wrapped carbon nanotube/Pt nanoparticles and poly[2,2'(2,6-phenyl)-5,5'-bibenzimidazole] (PBI) for both the anode and cathode catalysts and an electrolyte membrane material, respectively.. |
| 72. | JongTae Yoo, Sang Bong Lee, Chang Kee Lee, Sung Wook Hwang, ChaeRin Kim, Tsuyohiko Fujigaya, Naotoshi Nakashima, Jin Kie Shim, Graphene oxide and laponite composite films with high oxygen-barrier properties, NANOSCALE, 10.1039/c4nr03429e, 6, 18, 10824-10830, 2014.07, The design and fabrication of oxygen barrier films is important for both fundamental and industrial applications. We prepared three different thin films composed of graphene oxide (GO) and laponite (LN), a typical low cost inorganic clay, with the GO/LN volume ratios of 1.9/0.1, 1.7/0.3 and 1.5/0.5 together with a double layer film of the GO and LN. We found that the films with GO/LN=1.9/0.1 and the double layers exhibited high oxygen barrier and oxygen transmission rate values that reached 0.55 and 0.37 cm(3) per m(2) per atm per day, respectively, which were much lower than those of the films prepared from the pure GO, only LN and GO/LN=1.7/0.3 and 1.5/0.5. This study is important for the design and fabrication of a film from GO-based all inorganic nanomaterials for applications in gas-barrier membranes.. |
| 73. | Takahiro Fukumaru, Fumiyuki Toshimitsu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Effects of the chemical structure of polyfluorene on selective extraction of semiconducting single-walled carbon nanotubes, NANOSCALE, 10.1039/c4nr00809j, 6, 11, 5879-5886, 2014.06, The selective recognition/extraction of semiconducting (sem)- and metallic (met)-single-walled carbon nanotubes (SWNTs) is still a great challenge in the science and technology of carbon nanotubes because their selective synthesis is still difficult. Poly(9,9-dioctyl-fluorene-2,7-diyl) (2C8-PF) and its derivatives are widely used polymers in carbon nanotube science and technology since they only extract sem-SWNTs from the mixture of sem-/met-SWNTs, while the separation mechanism is still unclear. In this study, we focus on the alkyl chain number on the polyfluorenes (PFs) to understand the mechanism for selective recognition. Here we describe the synthesis of mono-octyl moiety-carrying polyfluorene (poly(9-octyl-9H-fluorene-2,7-diyl), C8H-PF), and characterized its selective SWNT recognition/extraction ability, and found that the C8H-PF solubilized sem-SWNTs with a diameter of 0.9-1.1 nm, whose behavior is similar to that of 2C8-PF. In addition, C8H-PF selectively extracted sem-SWNTs with larger diameters (average diameter = 1.4 nm), whose behavior is different from that of 2C8-PF. Molecular mechanics simulations were carried out to understand such specific solubilization behavior. This study provides an insight into the design and synthesis of PF-based polymers and copolymers that exhibit efficient selective sem-SWNT recognition/extraction ability and their applications.. |
| 74. | Syouhei Nishihama, Satomi Matsunaga, Seitaro Takayama, Tokie Ookubo, Kazuharu Yoshizuka, Tsuyohiko Fujigaya, Naotoshi Nakashima, Thermal-Swing Adsorption of Europium(III) with Poly(N-isopropylacrylamide) Combined with an Acidic Extractant, SOLVENT EXTRACTION RESEARCH AND DEVELOPMENT-JAPAN, 10.15261/serdj.21.37, 21, 37-45, 2014.05, A thermal-swing adsorption system for Eu(III) was developed using the thermosensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), combined with the acidic extractants, acid phosphoxy ethyl methacrylate (Phosmer-M) or acrylic acid. The phase transition of the PNIPAM/acidic extractant copolymers was successfully achieved by changing the temperature around the lower critical solution temperature (LCST). The thermal-swing adsorption of Eu(III) was correspondingly achieved by changing the temperature of the aqueous solution. The adsorption ability of Eu(III) was increased when the temperature became higher than the LCST, due to the change in the hydrophobicity as well as in the volume of the copolymer. The difference in the adsorption at lower and higher temperatures against the LCST was increased with decreasing crosslinldng agent during the preparation of the copolymer. The copolymer possessed sufficient loading and release capacity for Eu(III) even in repeated processes of the thermal-swing adsorption.. |
| 75. | Naoki Imazu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Fabrication of flexible transparent conductive films from long double-walled carbon nanotubes, SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS, 10.1088/1468-6996/15/2/025005, 15, 2, 2014.04, The fabrication of flexible transparent conducting films (TCFs) is important for the development of the next-generation flexible devices. In this study, we used double-walled carbon nanotubes (DWCNTs) as the starting material and described a fabrication method of flexible TCFs. We have determined in a quantitative way that the key factors are the length and the dispersion states of the DWCNTs as well as the weight-ratios of dispersant polymer/DWCNTs. By controlling such factors, we have readily fabricated a flexible highly transparent (94% transmittance) and conductive (surface resistivity = 320 Omega sq(-1)) DWCNT film without adding any chemical doping that is often used to reduce the surface resistivity. By applying a wet coating, we have succeeded in the fabrication of large-scale conducting transparent DWCNT films based on the role-to-role method.. |
| 76. | Tsuyohiko Fujigaya, ChaeRin Kim, Kazuya Matsumoto, Naotoshi Nakashima, Palladium-Based Anion- Exchange Membrane Fuel Cell Using KOH- Doped Polybenzimidazole as the Electrolyte, CHEMPLUSCHEM, 10.1002/cplu.201300377, 79, 3, 400-405, 2014.03, The development of a low-cost and high-performance fuel cell is a strong social demand. Anion-exchange membrane fuel cells (AEMFCs) have recently emerged as an alternative technology to conventional fuel cells that use a proton-exchange membrane as they enable the use of cheaper metals than platinum. An AEMFC exhibiting a maximum power density of 241mWcm(-2) based on a palladium-based electrocatalyst has been developed. The polybenzimidazole-wrapped carbon nanotubes were used to anchor the palladium nanoparticles, and the material was doped using KOH to form an ideal triple-phase boundary structure around the palladium. The observed maximum power density is the highest among previously reported AEMFCs using palladium as the metal catalyst.. |
| 77. | Takahiro Fukumaru, Yusuke Saegusa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Fabrication of Poly(p-phenylenebenzobisoxazole) Film Using a Soluble Poly(o-alkoxyphenylamide) as the Precursor, MACROMOLECULES, 10.1021/ma4024526, 47, 6, 2088-2095, 2014.03, Poly(p-phenylenebenzobisoxazole) (PPBO) is a polymer having the most excellent thermal properties among the organic polymers reported to date, and the design and the preparation of PPBO with the desired shape and form are expected to provide novel PPBO-based devices and materials in the fields of automobiles, aerospace, microelectronics, etc. We here describe the fabrication and characterization of PPBO films via the solution-casting and successive thermal conversion of its precursor, alkyl-substituted hydroxypolyamides (poly(o-alkoxyphenylamide)s) that were synthesized by a low-temperature polycondensation reaction of dialkoxydiaminobenzene with terephthaloyl chloride in N-methylpyrrolidone. The formation mechanism of the thermal conversion was carefully investigated based on the analyses of the results using TGA, IR, pyrolysis gas chromatography mass spectrometry (Py-GC/MS), and evolved gas analysis GC/MS (EGA-GC/MS) measurements. A transparent PPBO precursor film provided a PPBO film after thermal treatment at 250 degrees C for 6 h and then at 300 degrees C for 6 h under vacuum. The obtained PPBO film showed excellent mechanical properties (tensile strength = 76 MPa, Young's modulus = 2.7 GPa) as well as a high thermal stability (temperature of 5 wt % loss = 670 degrees C). Such outstanding mechanical and thermal properties would significantly contribute to fulfill the requirements for next generation extreme materials/devices.. |
| 78. | Mohamed R. Berber, Tsuyohiko Fujigaya, Naotoshi Nakashima, High-Temperature Polymer Electrolyte Fuel Cell Using Poly(vinylphosphonic acid) as an Electrolyte Shows a Remarkable Durability, CHEMCATCHEM, 10.1002/cctc.201300884, 6, 2, 567-571, 2014.02, The development of a high-performance, durable, and less expensive membrane electrode assembly (MEA) composed of a polymer electrolyte membrane and electrocatalysts is important for developing fuel cells. Herein, we described the design and fabrication of an electrocatalyst with carbon black, polybenzimidazole doped with poly(vinylphosphonic acid) (PVPA), and platinum nanoparticles as an electron-conducting support material, an electrolyte, and a metal catalyst, respectively. Most importantly, we used PVPA in place of phosphoric acid, which is a widely used acid dopant, as the acid dopant for both the electrocatalyst and the polymer electrolyte membrane. We reported that the use of PVPA is crucial for the high performance of the MEA because it prevented the leaching of acid molecules from the MEA, which led to high durability compared to that of the phosphoric acid-doped MEAs.. |
| 79. | Tsuyohiko Fujigaya, Shinsuke Hirata, Naotoshi Nakashima, A highly durable fuel cell electrocatalyst based on polybenzimidazole-coated stacked graphene, JOURNAL OF MATERIALS CHEMISTRY A, 10.1039/c3ta14469k, 2, 11, 3888-3893, 2014.01, We describe here the finding that, with the aid of poly(benzimidazole) (PBI), soluble graphene was obtained in solution by the exfoliation of graphite without introducing oxidative sites on graphene, and the homogeneous loading of Pt-nanoparticles onto the PBI-covered non-oxidized graphene was successful. The prepared electrocatalyst showed very high electrochemical durability; namely, the electrochemical surface area of the catalyst was not much different even after 2000-cyclic voltammogram (CV) cyclings, which is because there was no formation of Pt aggregates after CV cyclings. The durability of the synthesized fuel cell catalyst was much higher than that of the conventional Pt-loaded carbon black catalyst. The design of such high performance graphene-based fuel cell electrocatalysts is important for the development of next-generation polymer electrolyte fuel cells.. |
| 80. | Yusuke Tsutsumi, Tsuyohiko Fujigaya, Naotoshi Nakashima, Polymer synthesis inside a nanospace of a surfactant-micelle on carbon nanotubes: creation of highly-stable individual nanotubes/ultrathin cross-linked polymer hybrids, RSC ADVANCES, 10.1039/c3ra46841k, 4, 12, 6318-6323, 2013.12, We describe a novel synthetic method towards single-walled carbon nanotubes (SWNTs)/polymer hybrids utilizing the nanospace of a surfactant-micelle on the SWNTs, which provides highly stable SWNTs/ultrathin cross-linked polymer networks. In this study, N-isopropylacrylamide (NIPAM) is used as the monomer for the SWNT-wrapping. The prepared SWNTs wrapped by the poly(NIPAM) are stable even after freeze-drying/ redispersion cycles as well as after the addition of a large excess of surfactant molecules, and the stability is much higher than that of previously reported phospholipid-wrapped SWNTs that have been often used for the bio-applications of SWNTs. The present method is simple and opens a way to design and fabricate stable individually dissolved SWNT/polymer hybrids that are useful for many applications including bio-applications since a variety of (functional) monomers are readily applicable to the present method.. |
| 81. | Kohei Shimoda, Tsuyohiko Fujigaya, Naotoshi Nakashima, Yasuro Niidome, Spontaneous Temperature Control Using Reversible Spectroscopic Responses of PNIPAM-coated Gold Nanorods, CHEMISTRY LETTERS, 10.1246/cl.130457, 42, 10, 1247-1249, 2013.10, Poly(N-isopropylacrylamide) (PNIPAM) was coated on gold nanorods (NRs) without forming aggregates. The PNIPAM-coated NRs (PNIPAM-NRs) formed aggregates at higher temperature than the lower critical solution temperature (LCST) of the PNIPAM layers. The aggregation showed reversible spectroscopic responses under repeated temperature cycles. When a PNIPAM-NR solution was irradiated with near-infrared (near-IR) light, the temperature increased and aggregates formed showing broad and weak surface plasmon bands. The spectroscopic responses in near-IR work as a negative feedback for heating a photoirradiated nanorod solution. The feedback offers spontaneous temperature control of the photoirradiated solution at the LCST of PNIPAM.. |
| 82. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Advances in dispersal agents and methodology for SWNT analysis, Luminescence The Instrumental Key to the Future of Nanotechnology, 10.4032/9789814267724, 163-201, 2013.08. |
| 83. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Advances in dispersal agents and methodology for SWNT analysis, Luminescence: The Instrumental Key to the Future of Nanotechnology, 10.4032/9789814267724, 163-201, 2013.08. |
| 84. | Tsuyohiko Fujigaya, Minoru Okamoto, Kazuya Matsumoto, Kenji Kaneko, Naotoshi Nakashima, Interfacial engineering of platinum catalysts for fuel cells: Methanol oxidation is dramatically improved by polymer coating on a platinum catalyst, ChemCatChem, 10.1002/cctc.201300157, 5, 7, 1701-1704, 2013.07, All coated up: Platinum nanoparticles loaded on multiwalled carbon nanotubes (MWNTs) are coated with pyridine-containing polybenzimidazole (PyPBI). Interestingly, although a slight decrease in the accessibility of methanol is observed after coating, the methanol oxidation activity of Pt dramatically improves after coating with PyPBI. © 2013 WILEY-VCH Verlag GmbH & Co.. |
| 85. | JongTae Yoo, Tsuyohiko Fujigaya, Naotoshi Nakashima, Molecular recognition at the nanoscale interface within carbon nanotube bundles, NANOSCALE, 10.1039/c3nr01828h, 5, 16, 7419-7424, 2013.06, Molecular adsorption onto carbon nanotube surfaces is one of the important topics in the science and technology of carbon nanotubes due to their specific 1D structures with very high aspect ratios. In order to reveal the effect of bundles of single-walled carbon nanotubes (SWNTs) on molecular adsorption at the molecular level, we introduce an HPLC system; namely, we fabricated HPLC columns coated with bundled-SWNTs, isolated-SWNTs or graphene as the stationary HPLC phase, and discovered that polycyclic aromatic hydrocarbons having a one-dimensional shape, such as p-terphenyl and anthracene, exhibit an unusually high affinity to the bundled SWNTs compared to that of the isolated SWNTs. In contrast, no such notable specificity was obtained on a graphene-coated HPLC column. These results indicated that grooves with one-dimensional structures formed by the SWNT-bundles provide a favorable spatial geometry for the specific molecular recognition of aromatic hydrocarbons.. |
| 86. | 藤ヶ谷 剛彦, 中嶋 直敏, 福丸貴弘, Fabrication of Poly(p-phenylene benzobisoxazole) Film Using a Soluble Poly(o-alkoxyphenyl amide) as the Precursor, Macromolecules, 10.1021/ma4024526, 47, 2088-2095, 2013.05. |
| 87. | Mohamed R. Berber, Tsuyohiko Fujigaya, Kazunari Sasaki, Naotoshi Nakashima, Remarkably Durable High Temperature Polymer Electrolyte Fuel Cell Based on Poly(vinylphosphonic acid)-doped Polybenzimidazole, SCIENTIFIC REPORTS, 10.1038/srep01764, 3, 2013.05, studies have revealed that leaching of liquid phosphoric acid (PA) from both polymer electrolyte membrane and catalyst layers causes inhomogeneous PA distribution that results in deterioration of PEFC performance during long-term operation. Here we describe the finding that a novel PEFC free from acid leaching shows remarkable high durability (single cell test: >400,000 cycling) together with a high power density at 120 degrees C under a non-humidified condition. This is achieved by using a membrane electrode assembly (MEA) with Pt on poly(vinylphosphonic acid)-doped polybenzimidazole wrapped on carbon nanotube and poly(vinylphosphonic acid)-doped polybenzimidazole for the electrocatalst and electrolyte membrane, respectively. Such a high performance PEFC opens the door for the next-generation PEFC for "real world" use.. |
| 88. | Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Mechanical reinforcement of polybenzoxazole by carbon nanotubes through noncovalent functionalization, Macromolecules, 10.1021/ma4004117, 46, 10, 4034-4040, 2013.05, Polybenzoxazole (PBO) reinforced with carbon nanotubes (CNTs) is of great interest in the field of polymer composites because PBO and CNTs possess the highest-level mechanical properties among polymers and filler materials, respectively. However, the insolubility of PBO and the CNTs makes it difficult to develop a CNT/PBO composite in a solvent except for strong acids. In this study, we describe a novel strategy to design and prepare a CNT/PBO composite namely, a method using a PBO precursor having an excellent solubility in organic solvents. We discovered that a PBO precursor wraps CNTs though a strong interfacial interaction between the CNT surfaces and the PBO precursor that enables the dispersion of the CNTs in organic solvents. By this method, a CNT/PBO precursor composite film was easily obtained from the CNT/PBO composite solution, and by heating to 400 °C, we obtained a CNT/PBO composite film. Mechanical property measurements revealed that the CNT/PBO films exhibited a high tensile strength (151 MPa) and Young's modulus (8.1 GPa) at a CNT loading of 1.7 wt %, corresponding to 130% and 179% increase compared to those of the PBO film, respectively. These values are the highest values ever reported. Wrapping of the CNTs with PBO and the nice dispersion of the CNTs into a PBO matrix are considered to be important steps for the observed reinforcement. Indeed, scanning electron microscopic observations of the cross section of the CNT/PBO film indicated the homogeneous distribution of the isolated CNTs in the PBO film. This is the first example for the preparation of a CNT/PBO precursor film in an organic solvent based on a noncovalent CNT-functionalization. © 2013 American Chemical Society.. |
| 89. | Tsuyohiko Fujigaya, ChaeRin Kim, Kazuya Matsumoto, Naotoshi Nakashima, Effective anchoring of Pt-nanoparticles onto sulfonated polyelectrolyte-wrapped carbon nanotubes for use as a fuel cell electrocatalyst, POLYMER JOURNAL, 10.1038/pj.2012.145, 45, 3, 326-330, 2013.03, Sulfonated polymers, such as sulfonated polysulfone and sulfonated polyimide, are promising candidates as a future polyelectrolyte for polymer electrolyte fuel cells (PEFCs). In PEFC cell systems, the same polyelectrolyte material is often added to the electrocatalyst layer as the ionic path. We selected partially sulfonated poly(arylene thioethersulfone) (SPIES) and polyE(2,2'-benzidinedisulfonicacid)-alt-(1,4,5,8-naphthalenetetracarboxylic dianhydride)1 (BDSA-NTDA) as the electrolytes and wrapped multi-walled carbon nanotubes (MWNTs) with the materials to which platinum nanoparticles (Pt) were attached onto the polyelectrolyte layer to fabricate new electrocatalysts. In these electrocatalysts, the MWNT and Pt serve as the electron path and reaction site, respectively. For both polyelectrolytes, Pt-nanoparticles <5 nm in diameter with a narrow size distribution were observed to be homogeneously dispersed on the polymer-wrapped MWNTs. The electrochemical measurements revealed that MWNT/SPTES/Pt and MWNT/BDSA-NTDA/Pt possessed electrochemically active surface areas (ECSA) of 42.3 and 35.6 m(2)/g of Pt, respectively. Such a high ECSA efficiency ensures the use of these composites for the preparation of a future electrocatalyst. Polymer Journal (2013) 45, 326-330; doi:10.10381pj.2012.145; published online 1 August 2012. |
| 90. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Fuel Cell Electrocatalyst Using Polybenzimidazole-Modified Carbon Nanotubes As Support Materials, ADVANCED MATERIALS, 10.1002/adma.201204461, 25, 12, 1666-1681, 2013.03, Toward the next generation fuel cell systems, the development of a novel electrocatalyst for the polymer electrolyte fuel cell (PEFC) is crucial to overcome the drawbacks of the present electrocatalyst. As a conductive supporting material for the catalyst, carbon nanotubes (CNTs) have emerged as a promising candidate, and many attempts have been carried out to introduce CNT, in place of carbon black. On the other hand, as a polymer electrolyte, polybenzimidazoles (PBIs) have been recognized as a powerful candidate due to the high proton conductivity above 100 degrees C under non-humid conditions. In 2008, we found that these two materials have a strong physical interaction and form a stable hybrid material, in which the PBIs uniformly wrap the surfaces of the CNTs. Furthermore, PBIs serve as effective binding sites for the formation of platinum (Pt) nanoparticles to fabricate a ternary composite (CNT/PBIs/Pt). In this review article, we summarize the fundamental properties of the CNT/PBIs/Pt and discuss their potential as a new electrocatalyst for the PEFC in comparison with the conventional ones. Furthermore, potential applications of CNT/PBIs including use of the materials for oxygen reduction catalysts and reinforcement of PBI films are summarized.. |
| 91. | Haruka Koga, Takao Sada, Tsuyohiko Fujigaya, Naotoshi Nakashima, Kohji Nakazawa, Tailor-made cell patterning using a near-infrared-responsive composite gel composed of agarose and carbon nanotubes, Biofabrication, 10.1088/1758-5082/5/1/015010, 5, 1, 2013.03, Micropatterning is useful for regulating culture environments. We developed a highly efficient near-infrared-(NIR)-responsive gel and established a new technique that enables cell patterning by NIR irradiation. As a new culture substratum, we designed a tissue culture plate that was coated with a composite gel composed of agarose and carbon nanotubes (CNTs). A culture plate coated with agarose only showed no response to NIR irradiation. In contrast, NIR laser irradiation induced heat generation by CNTs this permitted local solation of the CNT/agarose gel, and consequently, selective cell-adhesive regions were exposed on the tissue culture plate. The solation area was controlled by the NIR intensity, magnification of the object lens and CNT concentration in the gel. Furthermore, we formed circular patterns of HeLa cells and linear patterns of 3T3 cells on the same culture plate through selective and stepwise NIR irradiation of the CNT/agarose gel, and we also demonstrated that individual 3T3 cells migrated along a linear path formed on the CNT/agarose gel by NIR irradiation. These results indicate that our technique is useful for tailor-made cell patterning of stepwise and/or complex cell patterns, which has various biological applications such as stepwise co-culture and the study of cell migration. © 2013 IOP Publishing Ltd.. |
| 92. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Development of electrocatalyst for anion-type polymer electrolyte fuel cell using KOH-doped polybenzimidazole, 12th Polymer Electrolyte Fuel Cell Symposium, PEFC 2012 - 222nd ECS Meeting Polymer Electrolyte Fuel Cells 12, PEFC 2012, 10.1149/05002.1919ecst, 1919-1925, 2012.12, Anion-exchange membrane fuel cells (AEMFC) are emerged as a alternative technology to overcome technical and cost issues of proton-exchange membrane fuel cells (PEMFC). In the present study, we describe a new electrocatalyst for AEMFC composed of carbon nanotubes (CNTs), KOH-doped polybenzimidazole (PBI) and platinum nanoparticles (Pt), in which CNTs are wrapped by KOH-doped PBI in nanometer thickness and Pt are efficiently loaded on the wrapping layer. In the electrocatalyst, it is revealed that CNTs and KOH-doped PBI layer functions as electron- and hydroxide-conductive path, respectively, and large exposed surface of Pt are allows an effective access of the fuel gas. Membrane electrode assembly fabricated with the electrocatalyst shows a high power density of 256 mW cm-2. To the best of our knowledge, this is the highest value in the AEMFC system measured in a similar experimental condition.. |
| 93. | Tsuyohiko Fujigaya, M. R. Berber, Naotoshi Nakashima, Durability of the electrocatalyst fabricated based on carbon nanotubes, 12th Polymer Electrolyte Fuel Cell Symposium, PEFC 2012 - 222nd ECS Meeting Polymer Electrolyte Fuel Cells 12, PEFC 2012, 10.1149/05002.1309ecst, 1309-1314, 2012.12, We describe the fabrication of a well-defined carbon nanotubes (CNTs)-based composite, in which the CNTs are individually wrapped by a polymer in homogeneous fashion and platinum nanoparticles (Pt) are immobilized on the polymer-wrapped CNTs. Polybenzimidazoles (PBIs) are used for the wrapping polymer since a strong adsorption of PBIs onto the CNT surfaces enables the exfoliation of CNT bundles and nanometer-thick PBI wrapping layer serves as a glue for the efficient immobilization of Pt. We demonstrate the use of the composite for the polymer electrolyte fuel cell (PEFC) electrocatalyst after acid doping. Single cell tests reveal that the ultra-thin PBI-wrapping layer around the CNTs serves as a proton conducting layer to deliver protons in the catalyst membrane. PEFCs using the composite show an excellent fuel cell performance at 120 °C under non-humid atmosphere, whereas the conventional Nafion-based PEFCs are not workable in such condition. Durability of the electrocatalyst was studied.. |
| 94. | Qingfeng Liu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Graphene unrolled from 'cup-stacked' carbon nanotubes, CARBON, 10.1016/j.carbon.2012.07.028, 50, 15, 5421-5428, 2012.12, High quality graphene with a large area and smooth edges has been obtained by unrolling the so-called 'cup-stacked' carbon nanotubes (CSCNTs) by the solution-phase oxidation and reduction. Atomic force microscopy and transmission electron microscopy observations reveal that the obtained graphene layers can even have a size of 20 mu m in width and 100 mu m in length, much larger than that of graphene unzipped from multi-walled carbon nanotubes. The low ratio of the D to G band intensities (within the 0.15-0.20 range) in Raman spectra indicates high quality of the obtained graphene, when compared to other graphene produced by the solution-phase oxidation. A formation mechanism is suggested for the graphene unrolled from the CSCNTs, providing an insight into the real microstructure of the CSCNTs, which are essentially continuous graphene layers rolled along the tube axis, yielding a pseudo cup-stacked like structure. (C) 2012 Elsevier Ltd. All rights reserved.. |
| 95. | T. Fujigaya, M. R. Berber, N. Nakashima, Durability of the electrocatalyst fabricated based on carbon nanotubes, ECS Transactions, 10.1149/05002.1309ecst, 50, 2, 1309-1314, 2012.10, We describe the fabrication of a well-defined carbon nanotubes (CNTs)-based composite, in which the CNTs are individually wrapped by a polymer in homogeneous fashion and platinum nanoparticles (Pt) are immobilized on the polymer-wrapped CNTs. Polybenzimidazoles (PBIs) are used for the wrapping polymer since a strong adsorption of PBIs onto the CNT surfaces enables the exfoliation of CNT bundles and nanometer-thick PBI wrapping layer serves as a glue for the efficient immobilization of Pt. We demonstrate the use of the composite for the polymer electrolyte fuel cell (PEFC) electrocatalyst after acid doping. Single cell tests reveal that the ultra-thin PBI-wrapping layer around the CNTs serves as a proton conducting layer to deliver protons in the catalyst membrane. PEFCs using the composite show an excellent fuel cell performance at 120 °C under non-humid atmosphere, whereas the conventional Nafion-based PEFCs are not workable in such condition. Durability of the electrocatalyst was studied. © The Electrochemical Society.. |
| 96. | T. Fujigaya, N. Nakashima, Development of electrocatalyst for anion-type polymer electrolyte fuel cell using KOH-doped polybenzimidazole, ECS Transactions, 10.1149/05002.1919ecst, 50, 2, 1919-1925, 2012.10, Anion-exchange membrane fuel cells (AEMFC) are emerged as a alternative technology to overcome technical and cost issues of proton-exchange membrane fuel cells (PEMFC). In the present study, we describe a new electrocatalyst for AEMFC composed of carbon nanotubes (CNTs), KOH-doped polybenzimidazole (PBI) and platinum nanoparticles (Pt), in which CNTs are wrapped by KOH-doped PBI in nanometer thickness and Pt are efficiently loaded on the wrapping layer. In the electrocatalyst, it is revealed that CNTs and KOH-doped PBI layer functions as electron- and hydroxide-conductive path, respectively, and large exposed surface of Pt are allows an effective access of the fuel gas. Membrane electrode assembly fabricated with the electrocatalyst shows a high power density of 256 mW cm-2. To the best of our knowledge, this is the highest value in the AEMFC system measured in a similar experimental condition. © The Electrochemical Society.. |
| 97. | H. Koga, T. Fujigaya, N. Nakashima, K. Nakazawa, Hepatocyte behaviors on single-walled carbon nanotubes, JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, 6, 360-361, 2012.09. |
| 98. | Kojiro Akazaki, Fumiyuki Toshimitsu, Hiroaki Ozawa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Recognition and One-Pot Extraction of Right- and Left-Handed Semiconducting Single-Walled Carbon Nanotube Enantiomers Using Fluorene-Binaphthol Chiral Copolymers, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja304244g, 134, 30, 12700-12707, 2012.08, Synthesized single-walled carbon nanotubes (SWNTs) are mixtures of right- and left-handed helicity and their separation is an essential topic in nanocarbon science. In this paper, we describe the separation of right- and left-handed semiconducting SWNTs from as-produced SWNTs. Our strategy for this goal is simple: we designed copolymers composed of polyfluorene and chiral bulky moieties because polyfluorenes with long alkyl-chains are known to dissolve only semiconducting SWNTs and chiral binaphthol is a so-called BINAP family that possesses a powerful enantiomer sorting capability. In this study, we synthesized 12 copolymers, (9,9-dioctylfluorene-2,7-diyl)x((R)- or (S)-2,2'-dimethoxy-1,1'-binaphthalen-6,6-diyl)y, where x and y are copolymer composition ratios. It was found that, by a simple one-pot sonication method, the copolymers are able to extract either right- or left-handed semiconducting SWNT enantiomers with (6,5)- and (7,5)-enriched chirality. The separated materials were confirmed by circular dichroism, vis- near IR and photoluminescence spectroscopies. Interestingly, the copolymer showed inversion of SWNT enantiomer recognition at higher contents of the chiral binaphthol moiety. Molecular mechanics simulations reveal a cooperative effect between the degree of chirality and copolymer conformation to be responsible for these distinct characteristics of the extractions. This is the first example describing the rational design and synthesis of novel compounds for the recognition and simple sorting of right- and left-handed semiconducting SWNTs with a specific chirality.. |
| 99. | Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Development of porous polybenzoxazole films using tert-buthoxycarbonyl group as a pore generator for patternable low dielectric constant materials, ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 244, 2012.08. |
| 100. | Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Extremely High Thermal Resistive Poly(p-phenylene benzobisoxazole) with Desired Shape and Form from a Newly Synthesized Soluble Precursor, MACROMOLECULES, 10.1021/ma3006526, 45, 10, 4247-4253, 2012.05, The poly(p-phenylene benzobisoxazole) (PPBO) fiber, known as Zylon, has a very high thermal stability as well as mechanical strength when compared to any other polymers due to its ladder-like rigid structure. However, one of the critical drawbacks of its stiff structure is its insolubility in organic solvents, and only strong acids can be used use for fiber spinning of this polymer. To overcome the poor processability caused by this insolubility in organic solvents, a soluble PPBO precursor was designed and synthesized by the reaction of tert-butyldimethylsilyl (TBS) group-functionalized 4,6-diaminoresoisinol with terephthaloyl chloride for polycondensation. The obtained TBS-functionalized PPBO precursor (TBS-prePBO) shows an excellent solubility in common organic solvents, such as N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO). Transparent TBS-prePBO films made by the solution-cast method provided PPBO films after thermal treatment at 500 degrees C for 1 h. The structure of the obtained PPBO films was characterized by IR and XRD techniques and found that the films exhibited extremely high thermal stabilities, namely, the synthesized PPBO polymer decomposition temperature reached 670 degrees C in flowing N-2, which is the highest temperature among the organic polymers reported so far.. |
| 101. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Soluble Carbon Nanotubes and Nanotube-Polymer Composites, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 10.1166/jnn.2012.6137, 12, 3, 1717-1738, 2012.03, For these two decade, tremendous amount of researches and developments dealing with carbon nanotubes (CNTs) have been carried out. Most of them are focusing on finding the unique and outstanding properties of CNTs and trying to utilizing them as the advanced materials. Whenever we start the research and the development of CNTs, the first difficulty is the dispersion of CNTs into the solvents since the CNTs form strong aggregation. Up to date, large efforts have been carried out for the preparation of CNT dispersion and the typical strategies are summarized. Such a dispersion technique allows us to use CNT as a material. Several applications of the CNT dispersion is also introduced.. |
| 102. | Syouhei Nishihama, Kayo Ohsawa, Yasushi Yamada, Kazuharu Yoshizuka, Tsuyohiko Fujigaya, Naotoshi Nakashima, Photo-swing extraction system for lanthanide separation by a thermosensitive polymer gel combined with carbon nanotubes, REACTIVE & FUNCTIONAL POLYMERS, 10.1016/j.reactfunctpolym.2011.12.001, 72, 2, 142-147, 2012.02, A novel photo-swing extraction system for lanthanide separation was developed using an acid phosphoxy ethyl methacrylate (Phosmer-M) copolymerized thermosensitive polymer gel and N-isopropylacrylamide (NIPAM) combined with single-walled carbon nanotubes (CNTs) as the extracting material. The swelling and shrinking phase transition of the Phosmer-M/NIPAM/CNT gel was successfully induced by photo-irradiation with a halogen lamp because of the heat generation by the CNTs, which occurred upon visible light absorption. The extraction ability of Eu(III) increased upon photo-irradiation because of changes in the volume and hydrophobicity of the composite gel. The ratio of the distribution coefficient with and without photo-irradiation (K-dphoto/K-d25) increased with an increase in the pH. The composite gel possessed sufficient loading and release capacities for Eu(III). La(III) and Lu(III) in repeated processes after photo-irradiation. The selectivity for Eu(III) over La(III) in binary metal systems increased due to photo-irradiation because the observed improvement in the extraction of Eu(III) was greater than that of La(III) during the phase transition of the gel. (C) 2011 Elsevier Ltd. All rights reserved.. |
| 103. | Hiroaki Ozawa, Tsuyohiro Fujigaya, Yasuro Niidome, Naotoshi Nakashima, Effect of Backbone Chemical Structure of Polymers on Selective (n,m)Single-Walled Carbon Nanotube Recognition/Extraction Behavior, CHEMISTRY-AN ASIAN JOURNAL, 10.1002/asia.201100362, 6, 12, 3281-3285, 2011.12, The development of a simple and facile method to extract single-walled carbon nanotubes (SWNTs) with a specific chirality index is one of the most-crucial issues in the fundamental study and applications of the SWNTs. We have compared the selective recognition/extraction of the SWNT chirality of poly(9,10-dioctyl-9,10-dihydrophenanthrene-2,7-diyl) (2C8-PPhO) to that of poly(9,9-dioctyfluoreny1-2,7-diyl) (2C8-PFO) that are able to extract specific semiconducting SWNTs free of any metallic SWNTs. Vis/NIR absorption, 2D photoluminescence, and Raman spectroscopy as well as molecular mechanical simulations were used to analyze and understand the obtained chiral selective solubilization behavior. We found that 2C8-PPhO selectively extracts and enriches the (8,6), (8,7), and (9,7)SWNTs, whose behaviors are different from that of 2C8-PFO, which preferentially extracts the (7,5), (7,6), (8,6), and (8,7)SWNTs. Our results indicate that 2C8-PPhO preferably recognizes larger-diameter SWNTs with higher chiral angles compared to those recognized by 2C8-PFO. These findings demonstrate that the difference in the non-aromatic ring numbers on the polymers results in different SWNT chirality recognition/extraction behaviors.. |
| 104. | Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Design and preparation of porous polybenzoxazole films using the tert-butoxycarbonyl group as a pore generator and their application for patternable low-k materials, POLYMER CHEMISTRY, 10.1039/c1py00470k, 3, 2, 369-376, 2011.12, The continuous advance of the device performance in microelectronics requires the development of the lower dielectric constant (low-k) materials. We target the development of a next generation low-k material based on poly(p-phenylene benzobisoxazole) (PPBO) films due to their low k value, remarkable mechanical toughness, excellent thermal stability, extremely low coefficient of thermal expansion and chemical inertness. In order to overcome the poor processability caused by the insolubility in organic solvents, the tert-butoxycarbonyl (t-Boc) group was introduced into the PPBO precursor (t-Boc-prePBO). The obtained t-Boc-prePBO shows excellent solubility in common organic solvents and fine films were successfully prepared. The thermal treatment of the t-Boc-prePBO film produces the PPBO film, which was completely characterized using IR. The low dielectric constant (k) value of 2.37 was achieved in the PPBO film. Scanning electron microscopy revealed the formation of a pore structure that plays an important role in the low k value of the film. The porous PPBO film also showed a good mechanical strength (16.0 MPa) and remarkably high thermal conductivity (0.445 W m(-1) K-1). Furthermore, the t-Boc functionalization enabled micropatterning using a photolithographic technique. Such a patternable film with a low k value, mechanical toughness, and high thermal conductivity is a promising candidate for the next generation low-k materials. Our calculation revealed that a k value could be lowered to 1.98 by controlling the film morphology, the value that satisfies the requirement of the International Technology Roadmap for Semiconductors (ITRS 2009).. |
| 105. | Hiroaki Ozawa, Natsuko Ide, Tsuyohiko Fujigaya, Yasuro Niidome, Naotoshi Nakashima, Supramolecular Hybrid of Metal Nanoparticles and Semiconducting Single-Walled Carbon Nanotubes Wrapped by a Fluorene-Carbazole Copolymer, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.201101669, 17, 48, 13438-13444, 2011.11, The first approach for the preparation of metal nanoparticle/semiconducting single-walled carbon nanotube (SWNT) hybrids with specified chirality is described. For this purpose, a copolymer of a fluorene derivative with two long-chain alkyl substituents and a carbazole derivative carrying a thiol group was used. The copolymer was found to selectively dissolve (7,6)- and (8,7)SWNTs, as determined by UV/Vis/NIR absorption and Raman spectroscopy and 2D photoluminescence mapping. Gold and silver nanoparticles with diameters of about 3.8 and about 3.2 nm, respectively, were readily attached along the SWNTs by means of coordination bonds between the nanoparticles and the thiol moieties on the copolymer, as revealed by atomic force and electron microscopy studies. The study provides a novel way to design and fabricate metal nanoparticle/semiconducting SWNT hybrids with specific nanotube chirality.. |
| 106. | Tsuyohiko Fujigaya, Yuki Yamamoto, Arihiro Kano, Atsushi Maruyama, Naotoshi Nakashima, Enhanced cell uptake via non-covalent decollation of a single-walled carbon nanotube-DNA hybrid with polyethylene glycol-grafted poly(L-lysine) labeled with an Alexa-dye and its efficient uptake in a cancer cell, NANOSCALE, 10.1039/c1nr10635j, 3, 10, 4352-4358, 2011.10, The use of single-walled carbon nanotubes (SWNTs) for biomedical applications is a promising approach due to their unique outer optical stimuli response properties, such as a photothermal response triggered by near-IR laser irradiation. The challenging task in order to realize such applications is to render the SWNTs biocompatible. For this purpose, the stable and homogeneous functionalization of the SWNTs with a molecule carrying a biocompatible group is very important. Here, we describe the design and synthesis of a polyanionic SWNT/DNA hybrid combined with a cationic poly(L-lysine) grafted by polyethylene glycol (PLL-g-PEG) to provide a supramolecular SWNT assembly. A titration experiment revealed that the assembly undergoes an approximately 1 : 1 reaction of the SWNT/DNA with PLL-g-PEG. We also found that SWNT/DNA is coated with PLL-g-PEG very homogeneously that avoids the non-specific binding of proteins on the SWNT surface. The experiment using the obtained supramolecular hybrid was carried out in vitro and a dramatic enhancement in the cell uptake efficiency compared to that of the SWNT/DNA hybrid without PLL-g-PEG was found.. |
| 107. | JongTae Yoo, Tsuyohiko Fujigaya, Naotoshi Nakashima, Facile Evaluation of interactions between Carbon Nanotubes and Phthalocyanines Using Silica Spheres Coated with Ultrathin-layers of Single-walled Carbon Nanotubes (vol 40, pg 538, 2011), CHEMISTRY LETTERS, 10.1246/cl.2011.1207, 40, 10, 1207-1207, 2011.10. |
| 108. | Tsuyohiko Fujigaya, Yasuhiko Tanaka, Naotoshi Nakashima, CNT/Polymer Composite Materials, Supramolecular Soft Matter Applications in Materials and Organic Electronics, 10.1002/9781118095331.ch18, 361-380, 2011.09. |
| 109. | Qingfeng Liu, Ayumi Ishibashi, Tsuyohiko Fujigaya, Kunitoshi Mimura, Takuya Gotou, Kazuyoshi Uera, Naotoshi Nakashima, Formation of self-organized graphene honeycomb films on substrates, CARBON, 10.1016/j.carbon.2011.04.038, 49, 11, 3424-3429, 2011.09, Mixing graphene oxide (GO) aqueous solution with tridodecylmethylammonium chloride (TDMAC) aqueous solution has gradually produced a precipitate of a complex of GO and TDMAC. The complex is soluble in many polar and nonpolar organic solvents, including low dielectric nonpolar organic solvents such as toluene and hexane. In addition, thin films cast the complex specified organic solutions under high humidity conditions have honeycomb-like structures with ordered self-organized macropores. Such insulating honeycomb films have become well conductive, when they were treated by the p-toluenesulfonicacid and then reduced by chemicals such as hydrazine or HI acid. (C) 2011 Elsevier Ltd. All rights reserved.. |
| 110. | Xun Yi, Gou Nakagawa, Hiroaki Ozawa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Tanemasa Asano, Ion Beam Bombardment Effect on Contacts in Solution-Processed Single-Walled Carbon Nanotube Thin Film Transistor, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.50.098003, 50, 9, 2011.09, Effect of argon ion bombardment (AIB) on performance of solution-processed single-walled carbon nanotube (SWCNT) thin film transistor (TFT) has been investigated. AIB was applied to the source/drain contacts to reduce contact resistance. It was found that AIB enhances on-state current of TFT. Over 5 decades' on/off ratio is obtained by applying AIB. Results of transmission line method using metallic SWCNT clearly indicate that contact resistance between CNT network and Au electrode is reduced by the application of AIB. (C) 2011 The Japan Society of Applied Physics. |
| 111. | Haruka Koga, Tsuyohiko Fujigaya, Naotoshi Nakashima, Kohji Nakazawa, Morphological and functional behaviors of rat hepatocytes cultured on single-walled carbon nanotubes, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 10.1007/s10856-011-4394-4, 22, 9, 2071-2078, 2011.09, This study describes the morphological and functional behaviors of rat hepatocytes on single-walled carbon nanotube (CNT)-coated surfaces. Although the hydrophobic characteristics of CNT-coated surfaces increased with increasing CNT density, hepatocyte adhesion decreased, indicating that the interaction between hepatocytes and CNTs is weak. We found that hepatocytes on a CNT-coated surface gradually gather together and form spheroids (spherical multicellular aggregates). These spheroids exhibit compact spherical morphology with a smooth surface and express connexin-32, an intracellular communication molecule. In contrast, collagen treatment in conjunction with the CNT-coated surface improved hepatocyte adhesion, and the cells maintained a monolayer configuration throughout the culture period. The albumin secretion and ammonia removal activities of hepatocyte spheroids were maintained at elevated levels for at least 15 days of culturing as compared with hepatocyte monolayers. These results indicate that CNTs can be used for the formation and long-term culture of hepatocyte spheroids.. |
| 112. | Hiroaki Ozawa, Xun Yi, Tsuyohiko Fujigaya, Yasuro Niidome, Tanemasa Asano, Naotoshi Nakashima, Supramolecular Hybrid of Gold Nanoparticles and Semiconducting Single-Walled Carbon Nanotubes Wrapped by a Porphyrin-Fluorene Copolymer, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja2055885, 133, 37, 14771-14777, 2011.09, We describe the design, synthesis, and characterization of a supramolecular hybrid of gold nanometals and semiconducting single-walled carbon nanotubes (SWNTs) wrapped by a porphyrin-fluorene copolymer (1), as well as fabrication of a thin-film transistor (TFT) device using the hybrid. Photoluminescence mapping revealed that the copolymer selectively dissolved SWNTs with chirality indices of (8,6), (8,7), (9,7), (7,6), and (7,5); dissolution of (8,6), and (8,7) SWNTs was especially efficient. The solubilized SWNTs were connected to gold nanoparticles (AuNPs) via a coordination bond to prepare a supramolecular hybrid composed of AuNPs/copolymer 1-wrapped SWNTs, which were studied by atomic force and scanning and transmission electron microscopies. A fabricated TFT device using the semiconducting SWNTs/copolymer 1 shows evident p-type transport with an On/Off ratio of similar to 10(5). The transport properties of the TFT changed after coordination of the AuNPs with the SWNTs/copolymer 1.. |
| 113. | Tsuyohiko Fujigaya, Yasuhiko Tanaka, Naotoshi Nakashima, CNT/Polymer Composite Materials, Supramolecular Soft Matter: Applications in Materials and Organic Electronics, 10.1002/9781118095331.ch18, 361-380, 2011.09. |
| 114. | Design and developments of carbon nanotube composite materials Carbon nanotubes (CNTs) are a class of conjugated polymer having an ultimate electronic and mechanical structure. Since the discovery of the CNTs, tremendous amount of efforts have been focused for the design and developments of CNT materials. Here, recent topics on the design and developments of CNT composite materials are described. © 2011 The Society of Polymer Science, Japan.. |
| 115. | Xun Yi, Hiroaki Ozawa, Gou Nakagawa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Tanemasa Asano, Single-Walled Carbon Nanotube Thin Film Transistor Fabricated Using Solution Prepared with 9,9-Dioctyfluorenyl-2,7-diyl-Bipyridine Copolymer, JAPANESE JOURNAL OF APPLIED PHYSICS, 10.1143/JJAP.50.070207, 50, 7, 2011.07, Performance of thin film transistor (TFT) whose channel is fabricated by using a solution process of single-walled carbon nanotube (SWCNT) has been studied. SWCNT solution is prepared by using 9,9-dioctyfluorenyl-2,7-diyl-bipyridine (PFO-BPy) copolymer as solubilizer. Over 4 decades' on/off ratio is obtained by using drop-coating at room temperature without any further optimization. Other solubilizers are chosen as control groups to measure the on/off ratio of SWCNT TFT to investigate effects of the use of PFO-BPy. Results suggest that thick SWCNT network should be uniformly established at the channel region and the channel is required to be formed with well-separated SWCNTs. (C) 2011 The Japan Society of Applied Physics. |
| 116. | JongTae Yoo, Hiroaki Ozawa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Evaluation of affinity of molecules for carbon nanotubes, NANOSCALE, 10.1039/c1nr10079c, 3, 6, 2517-2522, 2011.06, Recent developments of non-covalent functionalization of carbon nanotubes (CNTs) require a systematic understanding of the interaction between molecule and CNTs (CNT-molecular interaction); however, it has been difficult to evaluate the "net" interaction between the CNTs and molecules. We now use silica gel particles coated with the pristine single-walled carbon nanotubes (SWNTs) in a monolayer fashion as the stationary phase of a HPLC column. The newly developed column (SWNT-column) worked as a powerful tool for ranking the interactions between the SWNTs and molecules with a high precision. We describe the binding affinity analysis of polyaromatic hydrocarbons onto the surfaces of SWNTs. The obtained ranking is determined in the order of benzene < naphthalene < biphenyl < fluorene < phenanthrene < anthracene similar to pyrene < triphenylene < p-terphenyl < tetraphene < tetracene.. |
| 117. | Takao Sada, Tsuyohiko Fujigaya, Yasuro Niidome, Kohji Nakazawa, Naotoshi Nakashima, Near-IR Laser-Triggered Target Cell Collection Using a Carbon NanotubeBased Cell-Cultured Substrate, ACS NANO, 10.1021/nn2012767, 5, 6, 4414-4421, 2011.06, Unique near-IR optical properties of single-walled carbon nanotube (SWNTs) are of Interest in many biological applications. Here we describe the selective cell detachment and collection from an SWNT-coated cell-culture dish triggered by near-IR pulse laser Irradiation. First, Hela cells were cultured on an SWNT-coated dish prepared by a spraying of an aqueous SWNT dispersion on a glass dish. The SWNT-coated dish was found to show a good cell adhesion behavior as well as a cellular proliferation rate similar to a conventional glass dish. We discovered, by near-IR pulse laser irradiation (at the laser power over 25 mW) to the cell under optical microscopic observation, a quick single-cell detachment from the SWNT-coated surface. Shockwave generation from the irradiated SWNTs is expected to play an important role for the cell detachment. Moreover, we have succeeded in catapulting the target single cell from the cultured medium when the depth of the medium was below 150 pin and the laser power was stronger than 40 mW. The captured cell maintained its original shape. The retention of the genetic Information of the cell was confirmed by the polymerase chain reaction (PCR) technique. A target single-cell collection from a culture medium under optical microscopic observation is significant in wide fields of single-cell studies in biological areas.. |
| 118. | Tsuyohiko Fujigaya, Takeshi Uchinoumi, Kenji Kaneko, Naotoshi Nakashima, Design and synthesis of nitrogen-containing calcined polymer/carbon nanotube hybrids that act as a platinum-free oxygen reduction fuel cell catalyst, CHEMICAL COMMUNICATIONS, 10.1039/c1cc11303h, 47, 24, 6843-6845, 2011.05, The development of a platinum-free catalyst is one of the challenging issues for the global commercialization of fuel cell systems. Here we describe the design and synthesis of nitrogen-containing calcined polybenzimidazole/carbon nanotube hybrids that act as an oxygen reduction catalyst.. |
| 119. | JongTae Yoo, Tsuyohiko Fujigaya, Naotoshi Nakashima, Facile Evaluation of Interactions between Carbon Nanotubes and Phthalocyanines Using Silica Spheres Coated with Ultrathin-layers of Single-walled Carbon Nanotubes, CHEMISTRY LETTERS, 10.1246/cl.2011.538, 40, 5, 538-539, 2011.05, A simple and versatile method to evaluate the interactions between four different phthalocyanine dyes and carbon nanotube surfaces using silica spheres coated with ultrathin-layers of single-walled carbon nanotubes (SWNTs) is described. The well-isolated SWNTs immobilized on the silica spheres acted as effective adsorption sites for the dye molecules, and the interactions between them were evaluated by measuring the absorbance change in the supernatant solutions after simple mixing.. |
| 120. | Hiroaki Ozawa, Tsuyohiko Fujigaya, Suhee Song, Hongsuk Suh, Naotoshi Nakashima, Different Chiral Selective Recognition/Extraction of (n,m)Single-walled Carbon Nanotubes Using Copolymers Carrying a Carbazole or Fluorene Moiety, CHEMISTRY LETTERS, 10.1246/cl.2011.470, 40, 5, 470-472, 2011.05, We describe the finding that copolymers having a long-double chain carbazole or fluorene group connected to benzothiadiazole with thiophene linkers show a different chiral selective (n,m)single-walled carbon nanotube (SWNT) solubilization behavior which was revealed by 2D photoluminescence and vis near IR spectroscopies. We also carried out molecular mechanical simulations to understand the difference in the chiral selective solubilization behavior.. |
| 121. | Hiroaki Ozawa, Tsuyohiko Fujigaya, Yasuro Niidome, Naosuke Hotta, Michiya Fujiki, Naotoshi Nakashima, Rational Concept To Recognize/Extract Single-Walled Carbon Nanotubes with a Specific Chirality, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja109399f, 133, 8, 2651-2657, 2011.03, Single-walled carbon nanotubes (SWNTs) have remarkable and unique electronic, mechanical, and thermal properties, which are closely related to their chiralities; thus, the chirality-selective recognition/extraction of the SWNTs is one of the central issues in nanotube science. However, any rational materials design enabling one to efficiently extract/solubilize pure SWNT with a desired chirality has yet not been demonstrated. Herein we report that certain chiral polyfluorene copolymers can well-recognize SWNTs with a certain chirality preferentially, leading to solubilization of specific chiral SWNTs. The chiral copolymers were prepared by the Ni-0-catalyzed Yamamoto coupling reaction of 2,7-dibromo-9,9-di-n-decylfluorene and 2,7-dibromo-9,9-bis[(S)-(+)-2-methylbutyl]fluorene comonomers. The selectivity of the SWNT chirality was mainly determined by the relative fraction of the achiral and chiral side groups. By a molecular mechanics simulation, the cooperative interaction between the fluorene moiety, alkyl side chain, and graphene wall were responsible for the recognition/dissolution ability of SWNT chirality. This is a first example describing the rational design and synthesis of novel fluorene-based copolymers toward the ::recognition/extraction of targeted (n, m) chirality of the SWNTs.. |
| 122. | Kazuya Matsumoto, Tsuyohiko Fujigaya, Hiroyuki Yanagi, Naotoshi Nakashima, Very High Performance Alkali Anion-Exchange Membrane Fuel Cells, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.201001806, 21, 6, 1089-1094, 2011.03, Anion-exchange membrane fuel cells (AEMFCs) have emerged as an alternative technology to overcome the technical and cost issues of proton-exchange membrane fuel cells (PEMFCs). In this study, we describe a new electrocatalyst for AEMFCs composed of carbon nanotubes (CNTs), KOH-doped polybenzimidazole (PBI) and platinum nanoparticles (Pt), in which the CNTs are wrapped by KOH-doped PBI at a nanometer thickness and Pt is efficiently loaded on the wrapping layer. In the electrocatalyst, it is revealed that the CNTs and the KOH-doped PBI layer function as electron-and hydroxide-conductive paths, respectively, and the large exposed surface of the Pt allows an effective access of the fuel gas. Quantitative formation of the well-defined interfacial structure formed by these components leads to an excellent mass transfer in the catalyst interface and realizes a high fuel-cell performance. Membrane electrode assemblies fabricated with the electrocatalyst show a high power density of 256 mW cm(-2). To the best of our knowledge, this is the highest value for AEMFC systems measured in similar experimental conditions.. |
| 123. | Hiroaki Ozawa, Natsuko Ide, Tsuyohiko Fujigaya, Yasuro Niidome, Naotoshi Nakashima, One-pot Separation of Highly Enriched (6,5)-Single-walled Carbon Nanotubes Using a Fluorene-based Copolymer, CHEMISTRY LETTERS, 10.1246/cl.2011.239, 40, 3, 239-241, 2011.03, We now describe the finding that a copolymer of 9,9-dioctylfluorenyl-2,7-diyl and bipyridine (BPy) can extract in "one-pot" approximate to 96-97%-enriched (6,5)-SWNTs in m-xylene and p-xylene not containing metallic SWNTs, which was revealed by vis near IR absorption, photoluminescence, and Raman spectroscopies.. |
| 124. | Tsuyohiko Fujigaya, JongTae Yoo, Naotoshi Nakashima, A method for the coating of silica spheres with an ultrathin layer of pristine single-walled carbon nanotubes, CARBON, 10.1016/j.carbon.2010.09.043, 49, 2, 468-476, 2011.02, We describe a method to fabricate silica gel particles coated with a monolayer of pristine single-walled carbon nanotubes (SWCNTs). SWCNTs dissolved in 1-methyl-2-pyrrolidinone (NMP) are mixed with amino-functionalized silica gels having different diameters. Strong interaction between the amino group and the SWCNT surfaces induces the adsorption of the SWCNTs on the silica, while the stable solvation in NMP hampers further adsorption of the tubes. This approach enables the production of a homogeneous, nondestructive and high-yield coating of the SWCNTs onto the silica surfaces, especially for larger sphere with a diameter over 1 mu m. The density and bundling degree of the SWCNTs on the silica gel surfaces are finely controlled by simply changing the ratios of the SWCNTs to the silica gels as well as the SWCNT concentrations. We also describe the coating of the silica gels with metallic SWCNTs. The SWCNT-coated silica gels are useful for a wide range of materials, such as the stationary phase for liquid chromatography and catalyst supporting materials. (C) 2010 Elsevier Ltd. All rights reserved.. |
| 125. | Tsuyohiko Fujigaya, Tatsuro Morimoto, Naotoshi Nakashima, Isolated single-walled carbon nanotubes in a gel as a molecular reservoir and its application to controlled drug release triggered by near-IR laser irradiation, SOFT MATTER, 10.1039/c0sm01234c, 7, 6, 2647-2652, 2011.01, We describe the preparation of a single-walled carbon nanotube-based molecular container with a stimuli responsible releasable functionality. First, single-walled carbon nanotube (SWNT)-embedded composite gels are synthesized by the gelation of three different acrylamide derivatives including N-isopropylacrylamide (NIPAM), acrylamide and N, N-dimethylacrylamide (DMAAM) in the presence of individually dissolved SWNTs aided by aqueous micelles of sodium dodecylbenzenesulfonic acid (SDBS), and then the SDBS molecules were removed from the gels. The SWNTs remained isolated even after the removal of SDBS in the gel of NIPAM and copolymer gel of NIPAM and DMAAM, while the SWNTs dispersed in the gels of acrylamide and DMAAM formed bundle structures. The SWNT surfaces having large surface areas in the gel were thus obtained, then utilized as a scaffold for the adsorption of small hydrophilic molecules, such as an antineoplastic agent, doxorubicin hydrochloride (DOX). The SWNTs in the gel of NIPAM served as a molecular container to effectively hold the DOX molecules in basic aqueous media, and by lowering the pH, the DOX molecules on the SWNT surfaces were released into the bulk aqueous solution. Moreover, we have succeeded in the laser light-driven quick release of DOX molecules from the composite gel of NIPAM and DMAAM using a photothermal conversion effect of the SWNTs.. |
| 126. | Kazuya Matsumoto, Tsuyohiko Fujigaya, Kazunari Sasaki, Naotoshi Nakashima, Bottom-up design of carbon nanotube-based electrocatalysts and their application in high temperature operating polymer electrolyte fuel cells, JOURNAL OF MATERIALS CHEMISTRY, 10.1039/c0jm02744h, 21, 4, 1187-1190, 2010.11, We describe the fabrication of a well-defined carbon nanotube (CNT)-based composite, in which the CNTs are individually wrapped by a polymer in a homogeneous fashion and platinum nanoparticles (Pt) are immobilized on the polymer-wrapped CNTs. Polybenzimidazoles (PBIs) are used as the wrapping polymer since a strong adsorption of PBIs onto the CNT surfaces enables the exfoliation of CNT bundles and nanometre-thick PBI wrapping layer serves as a glue for the efficient immobilization of Pt. We demonstrate the use of the composite for the polymer electrolyte fuel cell (PEFC) electrocatalyst. The well-defined interfacial nanostructure of the composite enables efficient reactant diffusion, resulting in good oxygen reduction reaction activity. Single cell tests reveal that the ultra-thin PBI-wrapping layer around the CNTs serves as a proton conducting layer to deliver protons in the catalyst membrane. PEFCs using the composite show an excellent fuel cell performance at 120 degrees C under non-humid atmosphere, whereas the conventional Nafion-based PEFCs are not workable in such condition. Unique combination of the CNTs and PBIs provides a promising route for the next-generation high temperature PEFC.. |
| 127. | Qingfeng Liu, Tsuyohiko Fujigaya, Hui-Ming Cheng, Naotoshi Nakashima, Free-Standing Highly Conductive Transparent Ultrathin Single-Walled Carbon Nanotube Films, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja1067367, 132, 46, 16581-16586, 2010.11, Transparent and conductive single-walled carbon nanotube (SWNT) films are of great importance to a number of applications such as optical and electronic devices. Here, we describe a simple approach for preparing free-standing highly conductive transparent SWNT films with a 20-150 nm thickness by spray coating from surfactant-dispersed aqueous solutions of SWNTs synthesized by an improved floating-catalyst growth method. After the HNO3 treatment, dipping the SWNT films supporting on glass substrates in water resulted in a quick and nondestructive self-release to form free-standing ultrathin SWNT films on the water surface. The obtained films have sufficiently high transmittance (i.e., 95%), a very low sheet resistance (i.e., similar to 120 Omega/sq) and a small average surface roughness (i.e., similar to 3.5 nm for a displayed 10 x 10 mu m area). Furthermore, the floating SWNT films on the water surface were easily transferred to any substrates of interest, without intense mechanical and chemical treatments, to preserve their original sizes and network structures. For example, the transferred SWNT films on poly(ethylene terephthalate) films are mechanically flexible, which is a great advantage over conventional indium-tin oxide (ITO) and therefore strongly promise to be "post ITO" or many applications.. |
| 128. | Yuki Yamamoto, Tsuyohiko Fujigaya, Yasuro Niidome, Naotoshi Nakashima, Fundamental properties of oligo double-stranded DNA/single-walled carbon nanotube nanobiohybrids, NANOSCALE, 10.1039/c0nr00145g, 2, 9, 1767-1772, 2010.09, Fundamental properties of single-walled carbon nanotubes (SWNTs) that are individually dissolved using twenty base paired-double-stranded (ds) DNA, (dA)(20)/(dT)(20), as well as single-stranded (ss) twenty-mers of oligo DNAs, adenine (dA)(20) and thymine (dT)(20), for comparison are described. In this study, unbound oligo DNAs are fully removed from the hybrid aqueous solutions using size-exclusion chromatography (SEC)-HPLC. Each SEC chromatogram of the solutions shows two separated peaks; one is the free oligo DNAs and the others are the oligo DNA/SWNT hybrids. The earlier eluent fractions (the hybrids) are separated into four size-separated fractions, and then their stability is evaluated by the re-injection of the fractions. The chromatograms of the earlier eluent fractions are almost identical to those of the original ones even after storage for one month, indicating the high stability of the dsDNA/SWNTs and ssDNA/SWNTs hybrids in water. The results free us from considering the desorption of the bound-oligo dsDNA or oligo ssDNA from their nanohybrids with the SWNTs, which is of significant advantage to the utilization of oligo DNA/SWNT nanobiohybrids in wide areas of science. We also investigated the near-IR absorption and photoluminescence (PL) spectral behaviors of the fractionated oligo DNA/SWNTs hybrids not containing corresponding free oligo DNA.. |
| 129. | Tsuyohiko Fujigaya, Yasuhiko Tanaka, Naotoshi Nakashima, Soluble Carbon Nanotubes and Application to Electrochemistry, ELECTROCHEMISTRY, 10.5796/electrochemistry.78.2, 78, 1, 2-15, 2010.01, One of the key issues in the utilization of carbon nanotubes (CNTs) for basic researches as well as their applications is to develop a methodology to solubilize/disperse them in solvents. In this review articles, we first summarize individual solubilization of single-walled carbon nanotubes (SWNTs) in solvents using surfactants, polycylcic aromatic molecules, DNA and condensed polymers. We then describe a novel method determining the electronic states of individually dissolved SWNTs having an own chirality index based on the analysis of Nernst equation. We also introduce our recent approach toward the fabrication of a novel catalyst for fuel cell that works at a non-humid atmosphere using solubilized CNTs as material.. |
| 130. | Tsuyohiko Fujigaya, Minoru Okamoto, Naotoshi Nakashima, Design of an assembly of pyridine-containing polybenzimidazole, carbon nanotubes and Pt nanoparticles for a fuel cell electrocatalyst with a high electrochemically active surface area, CARBON, 10.1016/j.carbon.2009.07.038, 47, 14, 3227-3232, 2009.11, We describe the fabrication of a carbon nanotube (CNT) hybrid wrapped by pyridine-containing polybenzimidazole (PyPBI). PyPBI acts as an efficient dispersant for CNT wrapping and produces a stable complex after removal of the unbound PyPBI. We found that the wrapped PyPBI serve as a glue for immobilizing Pt nanoparticles onto the surface of multi-walled carbon nanotubes (MWCNTs) without any strong oxidation process for the MWCNTs, which is often used to produce sites where metallic nanoparticles are immobilized. Based on this method, a highly homogeneous and remarkably efficient Pt loading onto the surface of MWCNTs through a coordination reaction between Pt and PyPBI has been achieved. Cyclic voltammogram measurements have revealed that the Pt nanoparticles deposited on the PyPBI-wrapped MWCNTs have a high electrochemically active surface area. Present results provide useful information for the design and fabrication of triple-phase interface structures of fuel cell electrode catalysts with high efficient performance. (C) 2009 Elsevier Ltd. All rights reserved.. |
| 131. | Tsuyohiko Fujigaya, Takahiro Fukumaru, Naotoshi Nakashima, Evaluation of dispersion state and thermal conductivity measurement of carbon nanotubes/UV-curable resin nanocomposites, SYNTHETIC METALS, 10.1016/j.synthmet.2009.01.019, 159, 9-10, 827-830, 2009.05, We describe (i) the evaluation of bundled degrees of single-walled carbon nanotubes (SWNTs) in SWNT/UV-curable resin composite films based on the intensity change in the radial breading mode (RBM) of their Raman spectra at a 785-nm excitation, and (ii) the thermal conductivity measurements of the composites films using the temperature wave analysis method. The homogeneous dispersion of the SWNTs produced a gradual increase in the thermal conductivity with an increase in the SWNT loading up to 5.0 wt%. This observed behavior is quite different from that of the electric conductivity of the composite films, in which the electric conductivities dramatically decrease at around only a 0.05 wt%-SWNT loading as previously reported. (C) 2009 Published by Elsevier B.V.. |
| 132. | Minoru Okamoto, Tsuyohiko Fujigaya, Naotoshi Nakashima, Design of an Assembly of Poly(benzimidazole), Carbon Nanotubes, and Pt Nanoparticles for a Fuel-Cell Electrocatalyst with an Ideal Interfacial Nanostructure, SMALL, 10.1002/smll.200801742, 5, 6, 735-740, 2009.03, A newly designed and fabricated novel nanocomposite composed of multiwalled carbon nanotubes (MWNTs), poly (benzimidazole) (PBI),and Pt nanoparticles. This composite is fabricated by the preparation of PBI-wrapped MWNTs (MWNT/PBI), followed by Pt loading onto the MWNT/PBI. As a result of the PBI wrapping, the loading efficiency of the Pt nanoparticles onto the MWNTs is dramatically improved up to 58.8% compared to that of the pristine MWNTs (41.0%). The process also allows homogeneous Pt immobilization onto the surface of MWNTs without ally strong oxidation process for the MWNTs that is typically used for metal supporting on carbon nanotubes. Far-IR spectroscopy of the composite shows a peak from the Pt-N bonding, indicating that these improvements are derived from the coordination of the Pt ion with the PBI molecules. Cyclic voltammogram measurements reveal that the Pt nanoparticles deposited on the MWNT/PBI shows higher utilization efficiency (74%) for electrocatalysts compared to that on the pristine MWNT (39%).. |
| 133. | Nobuo Wakamatsu, Hisayoshi Takamori, Tsuyohiko Fujigaya, Naotoshi Nakashima, Self-Organized Single-Walled Carbon Nanotube Conducting Thin Films with Honeycomb Structures on Flexible Plastic Films, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200801241, 19, 2, 311-316, 2009.01, Complex 1, synthesized from anionic shortened single-walled carbon nanotubes and cationic ammonium lipid dissolved in organic solvents, is cast on pretreated transparent flexible poly(ethylene terephthalate) (PET) films under a higher relative humidity to form thin films with self-organized honeycomb structures. The cell sizes are controllable by changing the experimental conditions. The lipid, which is the cationic part of complex 1, is easily removed by a simple ion-exchange method, while maintaining the basic honeycomb structures. After the ion exchange, the nanotube honeycomb films on PET with thinner skeletons exhibit a dramatic decrease in the surface resistivity from insulating to conducting. Carbon nanotubes with honeycomb structures formed by the self-organization on flexible polymer films are useful in many areas of nanoscience and technology including nanomaterials, nanoelectronics, nanodevices, catalysts, sensors, and so on.. |
| 134. | Tsuyohiko Fujigaya, Tatsuro Morimoto, Yasuro Niidome, Naotoshi Nakashima, NIR Laser-Driven Reversible Volume Phase Transition of Single-Walled Carbon Nanotube/Poly(N-isopropylacrylamide) Composite Gels, ADVANCED MATERIALS, 10.1002/adma.200800494, 20, 19, 3610-+, 2008.10, Composite polymer gels composed of poly(N-isopropylacrylamide) and CNTs exhibit a repeatable volume phase transition between shrinkage and swelling upon ON/OFF NIR laser-light irradiation. The volume change is repeatable for more than 1200 cycles, indicating that the gel has an extremely high durability. The local and transient heat via the irradiation raised the temperature at the spot area in the get through a photothermal conversion effect of the CNTs, thus inducing this volume change.. |
| 135. | Tsuyohiko Fujigaya, Naotoshi Nakashima, Methodology for homogeneous dispersion of single-walled carbon nanotubes by physical modification, POLYMER JOURNAL, 10.1295/polymj.PJ2008039, 40, 7, 577-589, 2008.09, Science and technology on carbon nanotubes (CNTs) are an expanding field aiming at ascertaining their intrinsic properties and taking advantage of their inviting possibilities. Dealing with CNTs has faced the problem Of insolubility in both organic and inorganic solvents due to the strong interaction therein. Here we review the recent progress as well as our approaches to the solubilization of CNTs based on a physical modification method. Especially, the review focuses on the 'individual' solubilization of pristine CNTs in solvents. Individual solubilization of CNTs,is imperative in many research programs Such as chemical modification of CNTs via organic reactions, characterization of CNTs chiral indices as well as separation of these mixtures, preparation of composites with polymers, fabrication of CNTs-based nanoelectronics devices and so forth.. |
| 136. | Tsuyohiko Fujigaya, Shinsuke Haraguchi, Takahiro Fukumaru, Naotoshi Nakashima, Development of novel carbon nanotube/photopolymer nanocomposites with high conductivity and application to nanoimprint photolithography, ADVANCED MATERIALS, 10.1002/adma.200701780, 20, 11, 2151-+, 2008.06, UV-curable monomers provide an ideal mixture for the fabrication of composite materials containing single-walled carbon nanotubes (SWNTs) in terms of dispersion stability and excellent processablity. Precise patterns of SWNT composites on a sub-micrometer scale have been manufactured by nanoimprint lithography using a polydimethylsiloxane stamp.. |
| 137. | Minoru Okamoto, Tsuyohiko Fujigaya, Naotoshi Nakashima, Individual dissolution of single-walled carbon nanotubes by using polybenzimidazole, and highly effective reinforcement of their composite films, ADVANCED FUNCTIONAL MATERIALS, 10.1002/adfm.200701257, 18, 12, 1776-1782, 2008.06, Polvbenzimidazole (PBI) is shown to individually dissolve/disperse single-walled carbon nanotubes (SWNTs) in N,N-dimethylacetamide (DMAc), which is demonstrated by vis-near IR absorption and photoluminescence spectroscopy and atomic force microscopy observations. By casting these dispersions, SWNTs/PBI composite films were successfully fabricated on substrates without any sign of macroscopic aggregation. The thermal stability and mechanical properties of the composite films were investigated using thermogravimetric analysis (TGA) and tensile tests, respectively, and it was found that, first, the addition of SWNTs to PBI does not deteriorate the thermal stability of the matrix film, and second, the mechanical properties of the PBI film were reinforced by ca. 50% with only 0.06-wt % addition of the SWNTs to the film without reducing the thermal stability of the PBI. Raman spectroscopy of the composite films revealed the existence of an interaction between the PBI and the SWNTs. The individual dissolution of the SWNTs; and efficient reinforcement of the PBI are due to the pi-pi interaction between the PBI and the sidewalls of the SWNTs.. |
| 138. | Yuichi Noguchi, Tsuyohiko Fujigaya, Yasuro Niidome, Naotoshi Nakashima, Regulation of the near-IR spectral properties of individually dissolved single-walled carbon nanotubes in aqueous solutions of dsDNA, CHEMISTRY-A EUROPEAN JOURNAL, 10.1002/chem.200800070, 14, 19, 5966-5973, 2008.06, Two different single-walled carbon nanotubes (SWNTs), the so-called HiPco and CoMoCAT, have been individually dissolved in aqueous solutions of double-stranded DNA (dsDNA). Atomic force microscopy (AFM) revealed the fine structures of the dsDNA-wrapped SWNTs. The near-IR absorption and photoluminescence (PL) spectra of aqueous solutions of dsDNA-wrapped SWNTs were recorded and, in pure water, we observed only a single two-dimensional PL spot from (6,5) SWNTs for both HiPco and CoMoCAT. In sharp contrast, when Tris-EDTA (TE) buffer was used in place of pure water, the PL-mapping images of the solutions showed chirality indices of (6,5), (7,5), (7,6), (8,4), (9,4), and (10,2) for HiPco-SWNTs, and (6,5) and (7,5) for CoMo-CAT-SWNTs. The first semiconducting bands in the near-IR absorption spectra of solutions of dsDNA-wrapped SWNTs are different. To explain the observed differences in the near-IR absorption and PL behavior we conducted several experiments and found that the near-IR optical properties of the SWNTs can be modulated by changing the pH of the solutions. The pH breakpoints for near-IR absorption bleaching and PL quenching are different and the phenomena are explained by differences in the numbers of holes generated on the SWNTs. These findings are important from both fundamental and applied viewpoints.. |
| 139. | Jae-Won Jang, Raymond G. Sanedrin, Daniel Maspoch, Seongpil Hwang, Tsuyohiko Fujigaya, You-Moon Jeon, Rafael A. Vega, Xiaodong Chen, Chad A. Mirkin, Electrically biased nanolithography with KOH-coated AFM tips, NANO LETTERS, 10.1021/nl080418b, 8, 5, 1451-1455, 2008.05, This letter provides the first study aimed at characterizing the desorption and nanolithographic processes for SAM-coated, gold-coated silicon substrates oxidatively patterned with an AFM with a tip under potential control. The process either results in recessed patterns where the monolayer has been removed or raised structures where the monolayer has been removed and silicon oxidation has taken place. Eleven different SAMs have been studied, and the type of pattern formed depends markedly upon SAM chain length, end functional group, and applied bias. We show how local pH and choice of monolayer can be used to very effectively control the type of pattern that is ultimately formed. Interestingly, we show that hydroxide anion accessibility to the substrate surface is one of the most significant factors in determining the pattern topography. Moreover, control over the pattern topography can be achieved by controlling the concentration of the KOH in the water meniscus formed at the point of contact between tip and surface in the context of a bias-controlled DPN experiment with a KOH-coated tip. The work provides important insight into the factors that control SAM desorption and also ways of controlling the topography of features made in a potential-controlled scanning probe nanolithographic process.. |
| 140. | Yuichi Noguchi, Tsuyohiko Fujigaya, Yasuro Niidome, Naotoshi Nakashima, Single-walled carbon nanotubes/DNA hybrids in water are highly stable, CHEMICAL PHYSICS LETTERS, 10.1016/j.cplett.2008.02.089, 455, 4-6, 249-251, 2008.04, Unbound double-stranded DNA (dsDNA) was removed from an aqueous solution (solution 1) of dsDNA-solubilized single-walled carbon nanotubes (SWNTs) using size-exclusion chromatography (SEC). The SEC chromatogram of solution 1 showed two separated peaks, and the earlier eluent fraction was separated into four size-separated fractions, fr1-fr4, in which individually solubilized SWNTs were found to exist. The stability of the DNA/SWNT hybrids was evaluated by the re-injection of fr1-fr4. It was found that the chromatograms of fr1-fr4 were identical to those of the original ones even after storage for one month, indicating the high stability of the dsDNA/SWNT hybrids in water. (C) 2008 Elsevier B.V. All rights reserved.. |
| 141. | Hisayoshi Takamori, Tsuyohiko Fujigaya, Yoshifumi Yamaguchi, Naotoshi Nakashima, Simple preparation of self-organized single-walled carbon nanotubes with honeycomb structures, ADVANCED MATERIALS, 10.1002/adma.200602704, 19, 18, 2535-+, 2007.09, The spontaneous formation of self-assembled honeycomb-patterned structures from a single-walled carbon nanotube (SWNT) solution is shown. Simple solution casting of a SWNT-lipid conjugate (complex 1) on solid substrates is used. Microporous films (see figure) are cast from solutions of the complex in various solvents.. |
| 142. | Naotoshi Nakashima, Tsuyohiko Fujigaya, Fundamentals and applications of soluble carbon nanotubes, CHEMISTRY LETTERS, 10.1246/cl.2007.692, 36, 6, 692-697, 2007.06, In this review article, we describe i) a strategy for individual solubilization of single-walled carbon nanotubes (SWNTs) in water or organic solvents and ii) some fundamental properties and applications of the solubilized SWNTs.. |
| 143. | Jae-Won Jang, Daniel Maspoch, Tszcyohiko Fujigaya, Chad A. Mirkin, A "molecular eraser" for dip-pen nanolithography, SMALL, 10.1002/smll.200600679, 3, 4, 600-605, 2007.04, An erasing method for repairing defective nanostructures generated in a dip-pen nanolithography (DPN) using conductive tip and conductive atomic force microscope (c-AFM) to electrochemically induce desorption is described. c-AFM would be used to selectively desorb portions of a monolayer-based structure made by DPN with alkanethiol inks on gold. c-AFM is used to selectively control the elimination of 16-mercaptohexadecanoic acid (MHA) nanostructures. This erasing technique can be coupled with DPN, and the eliminated MHA features can be backfilled with a new ink by simply coating the cantilever with the desired molecule. This procedure results in the elimination of the MHA-based triangle and replacement with a 11-ferrocenyl-1-undecanethiol (FUT) based compound without a damage to the 1-octadecanethiol (ODT)-coated regions of the substrate.. |
| 144. | Tsuyohiko Fujigaya, Dong-Lin Jiang, Takuzo Aida, Spin-crossover physical gels: A quick thermoreversible response assisted by dynamic self-organization, CHEMISTRY-AN ASIAN JOURNAL, 10.1002/asia.200600371, 2, 1, 106-113, 2006.12, Iron(II) triazolate coordination polymers with lipophilic sulfonate counterions with alkyl chains of different lengths have been synthesized. In hydrocarbon solvents, these polymers formed a physical gel and showed a thermorrole in the spin-crossover event. The spin-transition temperature was tuned over a wide range by adding a small amount of 1-octanol, a scavenger for hydrogen-bonding interactions. This additive was essential for the iron(II) species to adopt a low-spin state. Com-eversible spin transition upon the sol-gel phase transition. The formation of a hydrogen-bonding network between the triazolate moieties and sulfonate ions, bridged by water molecules, was found to play an important role in the spin-crossover event. The spin-transition temperature was tuned over a wide range by adding a small amount of 1-octanol, a scavenger for hydrogen-bonding interactions. This additive was essential for the iron(II) species to adopt a low-spin state. Compared with nongelling references in aromatic solvents, the spin-crossover physical gels are characterized by their quick thermal response, which is due to a rapid restoration of the hydrogen-bonding network, possibly because of a dynamic structural ordering through an enhanced lipophilic interaction of the self-assembling components in hydrocarbon solvents.. |
| 145. | SW Lee, BK Oh, RG Sanedrin, K Salaita, T Fujigaya, CA Mirkin, Biologically active protein nanoarrays generated using parallel dip-pen nanolithography, ADVANCED MATERIALS, 10.1002/adma.200600070, 18, 9, 1133-+, 2006.05, Amine-active N-hydroxysuccinimide-terminated alkyl thiol templates are generated using parallel dip-pen nanolithography (DPN) and are used to covalently couple protein A/G. The protein arrays generated (see figure) are used to capture antibodies through affinity binding, while preserving their biological recognition properties. The versatility of the parallel DPN method for making many similar structures in a relatively high-throughput manner (14 000 dots in 10 min) is described.. |
| 146. | T Fujigaya, DL Jiang, T Aida, Spin-crossover dendrimers: Generation number-dependent cooperativity for thermal spin transition, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja050275k, 127, 15, 5484-5489, 2005.04, Poly(benzyl ether) dendrons having a focal triazole unit (Gntrz: trz = triazole; n = generation knumber = 0-2) were found to react with (MeSO3)(2)Fe to form dendritic coordination polymers ([Fe(Gntrz)3]-(MeSO3)(2)center dot 2H(2)O) that undergo the thermal spin transition. When the generation number of the dendritic unit was larger (n = 0 -> 1 -> 2), the average degree of polymerization (D-p = 20 -> 10 -> 3) and spin-crossover temperature (T-c = 335 - 315 - 300 K) of the resulting polymer were lower. However, the abruptness of the spin transition was not monotonically dependent on the generation number; (G1trz)Fe exhibited an abrupt spin transition with a temperature width of only 10 K, while the smallest and largest members of the (Gntrz)Fe family both displayed a rather broad spin-transition temperature width (30 (n = 0) and 50 K (n = 2)). X-ray diffraction and calorimetric analyses indicated the presence of a discotic columnar core-shell assembly with a crystal lattice best occupied by a C3v symmetric array of medium-sized (G1trz)-Fe.. |
| 147. | T Fujigaya, DL Jiang, T Aida, Switching of spin states triggered by a phase transition: Spin-crossover properties of self-assembled iron(II) complexes with alkyl-tethered triazole ligands, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 10.1021/ja038088e, 125, 48, 14690-14691, 2003.12, Iron(II) complexes of triazole derivatives having two C12 and C16 long alkyl chains, (C12trz)FeII and (C16trz)FeII, serve as novel spin-crossover materials, which display a spin-state transition in response to a phase transition. In contrast, a triazole complex with two C8 alkyl chains ((C8trz)FeII) exhibits only a poor response. EXAFS and XRD analyses of (C16trz)FeII indicate an interdigitating self-assembled structure of polynuclear iron(II) species. According to DSC, VT-IR, and VT-XRD profiles, the spin-state transition is triggered by melting of the interdigitating alkyl chains, which is likely responsible for the "lock-and-release" feature of the spin state. By virtue of the thermoreversibility of the phase transition, the spin crossover could be repeated without deterioration. Copyright © 2003 American Chemical Society.. |
| 148. | T Fujigaya, Y Sibasaki, S Ando, S Kishimura, M Endo, M Sasago, M Ueda, New photoresist materials for 157-nm lithography. Poly[vinylsulfonyl fluoride-co-4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)-styrene] partially protected with tert-butoxycarbonyl, CHEMISTRY OF MATERIALS, 10.1021/cm020198h, 15, 7, 1512-1517, 2003.04, Our molecular orbital calculations predicted excellent transparencies of molecules having sulfonyl fluoride groups in the vacuum ultraviolet (VUV) region. An optical density (OD) measurement of poly(vinylsulfonyl fluoride) [poly(VSF)] prepared by free radical polymerization of VSF clearly supported this calculation (OD = 2.1 mum(-1) at 157 nm). A new copolymer, poly [(VSF)(40)-co-4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene (HFISt)(60)] [poly(VSF40-co-HFISt(60))] prepared by free radical copolymerization of VSF and HFIST showed good transparency (OD = 2.4 mum(-1)) as well. Poly(VSF40-co-HFISt(22)-co-tert-butoxycarbonyl HFISt(38)) (OD = 2.8 mum(-1)) was prepared from poly(VSF40-co-HFISt(60)) and di-tert-butyl dicarbonate in the presence of 4-(dimethylamino)pyridine (DMAP). A resist film consisting of poly(VSF40-co-HFISt(22)-co-tert-Boc HFISt(38)) and 5 wt % triphenylsulfonium triflate showed a sensitivity of 7.2 mJ cm(-2) and a contrast of 3.1 when a 150-nm-thick film prebaked at 100 degreesC for 1 min was exposed to 157-nm laser, postbaked at 130 degreesC for 1 min, and developed with a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution.. |
| 149. | In, I, H Lee, T Fujigaya, M Okazaki, M Ueda, SY Kim, A new photoresist based on hyperbranched poly(arylene ether phosphine oxide), POLYMER BULLETIN, 10.1007/s00289-002-0114-z, 49, 5, 349-355, 2003.01, Hydroxy-terminated hyperbranched poly(arylene ether phosphine oxide) (P2) was synthesized via nucleophilic aromatic substitution reaction of AB(2) monomer, bis(4-hydroxyphenyl)-4'-fluorophenylphosphine oxide with K2CO3 as a base in NMP. The obtained polymer was dissolved well in NMP and DMSO, and casting of the solution gave a transparent film. The study on dissolution behavior of the film containing 10 wt% of diphenyliodonium-9,10-dimethoxyanthracene-2-sulfonate (DIAS) as a photoacid generator and 25 wt% of 4,4'-methylenebis-[2,6-bis(hydroxymethylphenyl) phenol] (MBHP) as a cross linker revealed that 0.5 wt% aqueous tetramthylammonium hydroxide (TMAH) solution was a suitable developer for this negative-type photoresist system. The photoresist system containing 10 wt% of DIAS and 25 wt% of MBHP showed the sensitivity of 9 mJ/cm(2) and the contrast of 1.6 when it was exposed to 365 nm light and postbaked at 120degreesC, followed by developing with 0.5 wt% aqueous TMAH solution at room temperature. The heat-treated (300degreesC, 30 min) negative image did not show any distortion.. |
| 150. | K Young-Gil, JB Kim, T Fujigaya, Y Shibasaki, M Ueda, A positive-working alkaline developable photoresist based on partially tert-Boc-protected calix[4]resorcinarene and a photoacid generator, JOURNAL OF MATERIALS CHEMISTRY, 10.1039/b106278f, 12, 1, 53-57, 2002.12, A positive working low- molecular- weight photoresist based on partially t- Boc protected tetra- C-methylcalix[ 4] resorcinarene (t- Boc C- 4- R) and a photoacid generator (PAG), diphenyliodonium 9,10- dimethoxyanthracene- 2- sulfonate (DIAS) has been developed. t- Boc C- 4- Rs were prepared by the reaction of C- 4- R with di- tert- butyl dicarbonate in the presence of 4- dimethylaminopyridine (DMAP). A clear film cast from a 20 wt% t- Boc C- 4- R solution in cyclohexanone showed high transparency to UV above 300 nm. The appropriate t- Boc protecting ratio was about 60 mol% in view of adhesion, deprotection temperature and dissolution rate. The photoresist consisting of 60 mol% t- Boc C- 4- R (95 wt%) and DIAS (5 wt%) showed a sensitivity of 13 mJ cm(-2) and a contrast of 12.6 when it was exposed to 365 nm light and postbaked at 105 degreesC for 90 s, followed by developing with a 2.38 wt% aqueous tetramethylammonium hydroxide (TMAH) solution at room temperature. A fine positive image featuring 1.5 mum of minimum line and space patterns was observed on the film of the photoresist exposed to 40 mJ cm(-2) of UV- light at 365 nm by the contact mode.. |
| 151. | S Ando, T Fujigaya, M Ueda, DFT calculations of photoabsorption spectra in the VUV region for design of photoresist materials for 157 nm lithography, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 10.2494/photopolymer.15.559, 15, 4, 559-568, 2002.08, Time-dependent density functional theory (TD-DFT) calculations using the B3LYP hybrid functional were performed to investigate the transparencies of organic molecules and polymers in the vacuum ultraviolet (VUV) region. The calculated photoabsorption spectra obtained from the combination of geometry optimization using the 6-311G(d) basis set and subsequent calculations of transition energies and oscillator strengths using the 6-311++G(d,p) basis set agree well with the experimental spectra. This method is a useful to infer the transparency of polymers in the VUV region, and in particular helpful for design of photoresist materials for F-2 lithography (157 nm). The transparencies of the model compounds relating to the representative polymer platforms were estimated, and the calculated spectra demonstrate the effectiveness of judicious introduction of -F and -CF3 groups in reducing optical absorption at the wavelength. In addition, the absorption spectra of model compounds having a sulfonyl fluoride (-SO2F) and sulfonyl ester (-SO2OR) groups, which were proposed by the present authors as novel resist platforms, were calculated and compared with the experimental spectra of corresponding homopolymers.. |
| 152. | T Fujigaya, Y Shibasaki, M Ueda, S Kishimura, M Eno, M Sasago, New photoresist material for 157 nm lithography., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 223, D76-D76, 2002.04. |
| 153. | S Ando, T Fujigaya, M Ueda, Density functional theory calculations of photoabsorption spectra of organic molecules in the vacuum ultraviolet region, JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS, 10.1143/JJAP.41.L105, 41, 2A, L105-L108, 2002.02, Time-dependent density functional theory (TD-DFT) calculations using the B3LYP hybrid functional were performed to investigate the transparencies of organic molecules in the vacuum ultraviolet (VUV) region. The calculated absorption spectra obtained from the combination of geometry optimization using the 6-311G(d) basis set and subsequent calculation of transition energies and oscillator strengths using the 6-311++G(d, p) basis set without empirical corrections agree well with the observed spectra reported by Brodsky et al. [J. Vac. Sci. & Technol. B 18 (2000) 3396]. This method is helpful to infer transparency of molecules in the VUV region and in particular useful for design of photoresist materials for F-2 lithography (157 nm).. |
| 154. | T Fujigaya, S Ando, Y Shibasaki, S Kishimura, M Endo, M Sasago, M Ueda, A new photoresist material for 157 nm lithography-2, JOURNAL OF PHOTOPOLYMER SCIENCE AND TECHNOLOGY, 10.2494/photopolymer.15.643, 15, 4, 643-654, 2002.01, Time-dependent density functional theory (TD-DFT) calculations using the B3LYP hybrid functional suggested that sulfonic acid esters are transparent at around 157 nm region. Based on these findings, poly(methyl vinyl sulfonate) [poly(VSO3Me)] was prepared and found to have an extremely low absorbance (Abs.) of 2.2 mum(-1) at 157 nm. Various alkyl vinyl sulfonates, (VSO3R)s were prepared from 2-chloroethanesulfonyl chloride and alcohol components in the presence of pyridine, and their radical polymerizations were conducted in bulk using 2,2'-azobis(isobutyronitrile) as an initiator. Polymerizations of primary and secondary VSO3Rs bearing small alkyl substituents gave homopolymers with high molecular weights. Among them, the Abs. of poly(2,2,2-trifluoroethyl vinyl sulfonate) reached to 1.3 mum(-1). Various copolymers from alkyl vinyl sulfonates and 4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)styrene (HFISt) were also prepared and the Abs. of poly(1,1,1,3,3,3-hexafluoroisopropyl vinyl sulfonate(40)-co-HFISt(60)) [poly(VSO3iPr6F(40)-co-HFISt(60))] was found to be 2.4 mum(-1) at 157 run. The photoresist consisting of partially t-BOC-protected poIy(VSO3iPr6F(40)-co-HFISt(28)-co-t-BOCHFISt(32)) (Abs. 2.6) and an photoacid generator showed the contrast and sensitivity of 10.3 and 5.0 mJ cm(-2), respectively.. |
| 155. | Tsuyohiko Fujigaya, Yuji Shibasaki, Mitsuru Ueda, A new positive working alkaline developable photoresist based on a simple amorphous molecule, tri(3,5-di-tert-butoxycarbonyloxybenzyl) 1,3,5-benzenetricarboxylate and a photoacid generator, Journal of Photopolymer Science and Technology, 10.2494/photopolymer.14.275, 14, 2, 275-280, 2001.08, A simple amorphous molecule, tri(3,5-di-tert-butoxycarbonyloxybenzyl) 1,3,5- benzenetetracarboxylate (4) was prepared from 1,3,5-benzenetricarbonyl trichloride (3) and 3,5-di(tert-butoxycarbonyloxy)benzyl alcohol (2). Compound 4 can form an uniform transparent film by spin-casting on silicone wafer and the film has a good transparency above 300 nm wavelength. The chemically amplified photoresist system based on 4 containing 5 wt% of diphenyliodonium 9,10-dimethoxyanthracene-2-sulfonate (DIAS) showed a sensitivity of 19 mJ/cm2 and a contrast of 17 with 365 nm light.. |
| 156. | Tsuyohiko Fujigaya, Mitsuru Ueda, A new photoresist based on poly(propyleneimine) dendrimer, Journal of Photopolymer Science and Technology, 10.2494/photopolymer.13.339, 13, 2, 339-344, 2000.08, Poly(propyleneimine)-based alkaline soluble dendrimer 2 was prepared by the Michael addition reaction of poly(propyleneimine) dendrimer (PPID) with N-(2-hydroxy-5-methylphenyl)-2-propenamide. The obtained 2 was well-dissolved in common organic solvents and its film was transparent above 300 nm. The dissolution behavior of the 2 film containing 30 wt% of 1-{1,1-bis[4-(2-diazo-1 (2H)naphthalenone-5-sulfonyloxy)-phenyl]ethyl}-4-{1-[4-(2-diazo-1 (2H)naphthalenone-5-sulfonyloxy)phenyl]-methylethyl}-benzene (DNQ) after exposure was studied and it was found that the conventional base developer, a 2.38 wt% aqueous tetramethylammonium hydroxide TMAH solution was too alkaline to obtain sufficient dissolution contrast. Therefore, a diluted TMAH developer [0.7 wt%] was used for the positive-type system. Then an unexposed area was completely insoluble, on the other hand an exposed area showed an adequate dissolution rate. The photoresist system containing 30 wt% of DNQ showed a sensitivity of 80 mJ/cm2 and a contrast of 5.3 with 365 nm light. A series of process, that is, imagewise exposure, heat treatment, flood exposure, and development for the resist system resulted in negative-type image.. |
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