Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Tsuyohiko Fujigaya Last modified date:2020.01.25

Professor / Molecular Information Chemistry / Department of Applied Chemistry / Faculty of Engineering

1. Edyta Turek, Tomohiro Shiraki, Tomonari Shiraishi, Tamehito Shiga, Tsuyohiko Fujigaya, Dawid Janas, Single-step isolation of carbon nanotubes with narrow-band light emission characteristics, Scientific reports, 10.1038/s41598-018-37675-4, 9, 1, 2019.12, Lack of necessary degree of control over carbon nanotube (CNT) structure has remained a major impediment factor for making significant advances using this material since it was discovered. Recently, a wide range of promising sorting methods emerged as an antidote to this problem, all of which unfortunately have a multistep nature. Here we report that desired type of CNTs can be targeted and isolated in a single step using modified aqueous two-phase extraction. We achieve this by introducing hydration modulating agents, which are able to tune the arrangement of surfactants on their surface, and hence make selected CNTs highly hydrophobic or hydrophilic. This allows for separation of minor chiral species from the CNT mixture with up to 99.7 ± 0.02% selectivity without the need to carry out any unnecessary iterations. Interestingly, our strategy is also able to enrich the optical emission from CNTs under selected conditions..
2. 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..
3. 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–O2 battery cathode, Polymer Journal, 10.1038/s41428-019-0207-2, 51, 9, 921-927, 2019.09, In the development of lithium (Li)–oxygen (O<sub>2</sub>) rechargeable batteries, the improvement of the rechargeability is one of the key issues to be solved. Herein, a novel strategy to solve this issue is explored using polymer-wrapped single-walled carbon nanotubes (SWCNTs) as the cathode material. Poly[2,2’-(2,6-pyridine)-5,5’-bibenzimidazole] (PyPBI), employed as the wrapping polymer of the SWCNTs, served to coordinate Li ions and to facilitate a favorable deposition of the discharge products on the SWCNTs during the discharge reaction at the cell cathode. As a result, the rechargeability of the cell (SWCNT/PyPBI-cell) was improved compared to the cell having nonwrapped SWCNTs as the cathode (SWCNT-cell)..
4. 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..
5. 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..
6. Tsuyohiko Fujigaya, Development of thermoelectric conversion materials using carbon nanotube sheets, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20180272, 400-408, 2019.01, Recently, thermoelectric (TE) conversion has attracted strong interests toward converting waste heat to electrical potential for applications such as portable and wearable electronic devices. Among a number of different candidates including inorganic and polymeric materials, single-walled carbon nanotubes (SWCNT) are particularly attractive due to their non-toxicity, material abundance, solution processability, remarkable electrical conductivity and so on. Here, progress in TE research based on SWCNT sheets is reviewed mainly for air stabilization of n-type SWCNT sheets and the TE properties of semiconducting SWCNT sheets..
7. Tomohiro Shiraki, Yoshiaki Niidome, Fumiyuki Toshimitsu, Tomonari Shiraishi, Tamehito Shiga, Boda Yu, Tsuyohiko Fujigaya, Solvatochromism of near infrared photoluminescence from doped sites of locally functionalized single-walled carbon nanotubes, Chemical Communications, 10.1039/c9cc00829b, 55, 25, 3662-3665, 2019.01, The doped sites of locally functionalized single-walled carbon nanotubes emit red-shifted and bright near-infrared photoluminescence compared to non-doped nanotubes. Here, we observe unique photoluminescent solvatochromism. Organic solvent environments induce photoluminescent energy shifts that linearly correlate with a solvent polarity function. A high responsiveness at the doped sites is found..
8. W. Huang, F. Toshimitsu, K. Ozono, M. Matsumoto, A. Borah, Y. Motoishi, K. H. Park, J. W. Jang, Tsuyohiko Fujigaya, Thermoelectric properties of dispersant-free semiconducting single-walled carbon nanotubes sorted by a flavin extraction method, Chemical Communications, 10.1039/c8cc10264c, 55, 18, 2636-2639, 2019.01, Semiconducting single-walled carbon nanotubes (s-SWNTs) were extracted from SWNT mixtures using a flavin derivative (FC12). We evaluated the thermoelectric properties of the s-SWNT sheets. Electrical conductivity, power factor and figure of merit values of the sheets were increased by two orders of magnitude after removing FC12 simply by dipping in dichloromethane..
9. Wenxin Huang, Eriko Tokunaga, Yuki Nakashima, Tsuyohiko Fujigaya, Thermoelectric properties of sorted semiconducting single-walled carbon nanotube sheets, Science and Technology of Advanced Materials, 10.1080/14686996.2019.1567107, 20, 1, 97-104, 2019.01, Single-walled carbon nanotubes (SWNTs), especially their semiconducting type, are promising thermoelectric (TE) materials due to their high Seebeck coefficient. In this study, the in-plane Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ) of sorted semiconducting SWNT (s-SWNT) free-standing sheets with different s-SWNT purities are measured to determine the figure of merit ZT. We find that the ZT value of the sheets increases with increasing s-SWNT purity, mainly due to an increase in Seebeck coefficient while the thermal conductivity remaining constant, which experimentally proved the superiority of the high purity s-SWNT as TE materials for the first time. In addition, from the comparison between sorted and unsorted SWNT sheets, it is recognized that the difference of ZT between unsorted SWNT and high-purity s-SWNT sheet is not remarkable, which suggests the control of carrier density is necessary to further clarify the superiority of SWNT sorting for TE applications..
10. 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, 2019.01, 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..
11. Tomohiro Shiraki, Boda Yu, Tomonari Shiraishi, Tamehito Shiga, Tsuyohiko Fujigaya, Meta-linkage design of bis-aryldiazonium modifiers for wavelength tuning of near infrared photoluminescence from locally functionalized single-walled carbon nanotubes, Chemistry Letters, 10.1246/cl.190203, 48, 8, 791-794, 2019.01, Local chemical functionalization of single-walled carbon nanotubes has been reported to modulate their near infrared photoluminescence (PL), where defect doping creates new emissive sites on the nanotubes. Previously, we reported on proximal defect doping with the use of bis-aryldiazonium salts, which considerably red-shifted nanotube PL (>1200 nm). In this study, we achieved PL modulation with newly designed bis-aryldiazonium modifiers having meta-linked methylene spacers. The spacer length-dependent wavelength shifts were greater than those of our previous para-linkage design..
12. Mohamed R. Berber, Tsuyohiko Fujigaya, Naotoshi Nakashima, A potential polymer formulation of a durable carbon-black catalyst with a significant fuel cell performance over a wide operating temperature range, Materials Today Energy, 10.1016/j.mtener.2018.08.016, 10, 161-168, 2018.12, Polymer electrolyte membrane fuel cells (PEMFCs) that quickly operate at relatively low temperatures, while generating a high-power output is of particular interest, especially for portable devices, since no external power source is required to reach the highest power at higher operating temperatures. Here, we describe the temperature-dependence and the performance of a membrane electrode assembly (MEA) of a newly fabricated fuel cell catalyst of carbon black (CB) which was functionalized for the first time by two conductive polymers; i.e., polybenzimidazole and Nafion. The fabricated MEA quickly operated at room temperature, providing a power density of 130 mW/cm2 (172 mW/mgPt) and 174 mW/cm2 (230 mW/mgPt) under 50% RH and 100% RH conditions, respectively. It also showed a remarkable durability (900-h long-term durability testing and 100,000 potential-stress cyclings) with a maximum power density of 250 mW/cm2 (330 mW/mgPt) at 60 °C. The electrochemical impedance spectroscopy (EIS) analysis showed an enhanced ionic conductivity of the assembled MEA at low temperatures due to the fabrication design which provided more useful conductive pathways for the smooth proton transport on the polymer's backbone. The results of this research satisfies the market demands, and offer reasonably priced materials with a remarkable performance and durability. In addition, it will stimulate industrial researchers to be involved in similar activities..
13. Tomohiro Shiraki, Tamehito Shiga, Tomonari Shiraishi, Hisashi Onitsuka, Naotoshi Nakashima, Tsuyohiko Fujigaya, 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, Local chemical functionalization is used for defect doping of single-walled carbon nanotubes (SWNTs), to develop near-infrared photoluminescence (NIR PL) properties. We report the multistep wavelength shifting of the NIR PL of SWNTs through chemical reactions at local doped sites tethered to an arylaldehyde group. The PL wavelength of the doped SWNTs is modulated based on imine chemistry. This involves the imine formation of aldehyde groups with added arylamines, imine dissociation reaction, exchange reaction of bound arylamines in the imine, and the Kabachnik–Fields reaction of imine groups using diisopropyl phosphite. Using doped sites as a localized chemical reaction platform can exploit the versatile molecularly driven functionality of carbon nanotubes and related nanomaterials..
14. Ki Hong Park, Seung Hoon Lee, Fumiyuki Toshimitsu, Jihoon Lee, Sung Heum Park, Tsuyohiko Fujigaya, Jae Won Jang, Gate-enhanced exciton-phonon coupling in photocurrent of (6,5) single-walled carbon nanotube based visible sensing field effect transistor, Carbon, 10.1016/j.carbon.2018.07.002, 139, 709-715, 2018.11, A visible sensing field effect transistor (FET) with a channel length of 100 nm for individual (6,5) single-walled carbon nanotubes (SWCNTs) is fabricated via a selective sorting method using 9,9-dioctyfluorenyl-2,7-diyl–bipyridine (PFO–BPy) polymer. The FET of the (6,5) SWCNTs shows p-type behavior with hundreds of on-off ratios and on-state conductivity of 50 ± 4.0 (Ω m)
. In addition, the photocurrent of the FET of the (6,5) SWCNTs in the visible range increases (maximum 200 times at 620 nm) with higher gate voltage. E
transition and PFO-BPy transition are observed in the FET of the (6,5) SWCNTs without application of a gate voltage. Interestingly, exciton-phonon coupled E
transition due to gate-doping (p-type), which has been reported in photoluminescence and absorption studies, is expected to occur in the photocurrent of the FET at negatively higher gate voltage (≤−4 V). In addition, the exciton-phonon coupled E
transition is prominently observable when carrier concentration by gate doping becomes approximately two-hundred sixty times (260 ± 43) larger than carrier concentration without application of a gate voltage. This demonstration would be useful for the development of SWCNT-based visible sensors with gate control in the SWCNT devices..
15. Hisashi Onitsuka, Tsuyohiko Fujigaya, Naotoshi Nakashima, Tomohiro Shiraki, Control of the Near Infrared Photoluminescence of Locally Functionalized Single-Walled Carbon Nanotubes via Doping by Azacrown-Ether Modification, Chemistry - A European Journal, 10.1002/chem.201800904, 24, 37, 9393-9398, 2018.07, Doped semiconducting single-walled carbon nanotubes (SWNTs) through local chemical functionalization (lf-SWNTs) show fascinating photoluminescence (PL) that appears with a longer wavelength and enhanced quantum yield compared to the original PL of non-modified SWNTs. In this study, we introduce an azacrown ether moiety at the doped sites of lf-SWNTs (CR-lf-SWNTs), and observe selective PL wavelength shifts depending on different interaction modes of silver ion inclusion and protonation of the amino group in the ring. Interestingly, their different values of the wavelength shifts show a clear correlation with calculated electron density of the nitrogen atom in the azacrown moiety in case of the inclusion form and the protonated form. This newly-observed responsiveness based on molecular interactions is expected to create doped sites that can versatilely control the PL functions based on molecular systems..
16. Kulbir K. Ghuman, Tsuyohiko Fujigaya, Electronic Structure of a Polybenzimidazole-Wrapped Single-Wall Carbon Nanotube, Journal of Physical Chemistry C, 10.1021/acs.jpcc.8b00247, 122, 28, 15979-15985, 2018.07, Polymer wrapping on a carbon nanotube (CNT) surface by polybenzimidazoles (PBIs) allows us to immobilize platinum nanoparticles on pristine CNTs and to use it as the electrocatalyst of polymer electrolyte membrane fuel cells (PEMFCs), thereby improving the durability of PEMFCs. In this work, for the first time, we present the fundamental insights into the electronic structure and the interaction present in the single-wall CNT (SWCNT) and PBI composite through comprehensive theoretical study supported by experiments. Our analyses predict that PBI possesses stable helical wrapping around SWCNT because of the strong noncovalent π-π interaction between them, in which PBI participates more than SWCNTs. It is also found that the functionalization of SWCNTs by PBI is independent of the SWCNT chiralities and that the functionalization does not affect the intrinsic properties of SWCNTs, making the SWCNT/PBI-based membrane electrode assembly a good candidate for high-performance PEMFCs..
17. Yukiko Nagai, Yusuke Tsutsumi, Naotoshi Nakashima, Tsuyohiko Fujigaya, Synthesis of Single-Walled Carbon Nanotubes Coated with Thiol-Reactive Gel via Emulsion Polymerization, Journal of the American Chemical Society, 10.1021/jacs.8b03873, 140, 27, 8544-8550, 2018.07, Single-walled carbon nanotubes (SWNTs) have unique near-infrared absorption and photoemission properties that are attractive for in vivo biological applications such as photothermal cancer treatment and bioimaging. Therefore, a smart functionalization strategy for SWNTs to create biocompatible surfaces and introduce various ligands to target active cancer cells without losing the unique optical properties of the SWNTs is strongly desired. This paper reports the design and synthesis of a SWNT/gel hybrid containing maleimide groups, which react with various thiol compounds through Michael addition reactions. In this hybrid, the method called carbon nanotube micelle polymerization was used to noncovalently modify the surface of SWNTs with a cross-linked polymer gel layer. This method can form an extremely stable gel layer on SWNTs; such stability is essential for in vivo biological applications. The monomer used to form the gel layer contained a maleimide group, which was protected with furan in endo-form. The resulting hybrid was treated in water to induce deprotection via a retro-Diels-Alder reaction and then functionalized with thiol compounds through Michael addition. The functionalization of the hybrid was explored using a thiol-containing fluorescent dye as a model thiol, and the formation of the SWNT-dye conjugate was confirmed by energy transfer from the dye to SWNTs. Our strategy offers a promising SWNT-based platform for biological functionalization for cancer targeting, imaging, and treatment..
18. Sumit Verma, Yuki Hamasaki, Chaerin Kim, Wenxin Huang, Shawn Lu, Huei Ru Molly Jhong, Andrew A. Gewirth, Tsuyohiko Fujigaya, Naotoshi Nakashima, Paul J.A. Kenis, Insights into the Low Overpotential Electroreduction of CO2 to CO on a Supported Gold Catalyst in an Alkaline Flow Electrolyzer, ACS Energy Letters, 10.1021/acsenergylett.7b01096, 3, 1, 193-198, 2018.01, Cost competitive electroreduction of CO2 to CO requires electrochemical systems that exhibit partial current density (jCO) exceeding 150 mA cm-2 at cell overpotentials (|ηcell|) less than 1 V. However, achieving such benchmarks remains difficult. Here, we report the electroreduction of CO2 on a supported gold catalyst in an alkaline flow electrolyzer with performance levels close to the economic viability criteria. Onset of CO production occurred at cell and cathode overpotentials of just -0.25 and -0.02 V, respectively. High jCO (∼99, 158 mA cm-2) was obtained at low |ηcell| (∼0.70, 0.94 V) and high CO energetic efficiency (∼63.8, 49.4%). The performance was stable for at least 8 h. Additionally, the onset cathode potentials, kinetic isotope effect, and Tafel slopes indicate the low overpotential production of CO in alkaline media to be the result of a pH-independent rate-determining step (i.e., electron transfer) in contrast to a pH-dependent overall process..
19. Koichiro Mori, Minoru Kawaguchi, Tsuyohiko Fujigaya, Jun Ohno, Tetsuro Ikebe, 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, 2018.01, 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..
20. Tomoya Shimono, Masaya Matsuki, Teppei Yamada, Masa-Aki Morikawa, Nobuhiro Yasuda, Tsuyohiko Fujigaya, Nobuo Kimizuka, Selective ionic conduction in choline iodide/triiodide solid electrolyte and its application to thermocells, Chemistry Letters, 10.1246/cl.171069, 47, 3, 261-264, 2018.01, 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..
21. Keita Ozono, Masashi Fukuzawa, Fumiyuki Toshimitsu, Tomohiro Shiraki, Tsuyohiko Fujigaya, Naotoshi Nakashima, Chiral Selective Chemical Reaction of Flavin-Derivative-Wrapped Semiconducting Single-Walled Carbon Nanotubes Based on a Specific Recognition, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20180206, 91, 11, 1646-1651, 2018.01, A specific chiral selective chemical reaction on flavinwrapped single-walled carbon nanotubes (SWNTs) is recognized based on a unique assembled structure formation of the flavin when using a chlorinated solvent such as chloroform; namely, the self-assembled flavin onto the SWNT surface protected (8,6)SWNTs from the chlorine radical reaction..
22. Huei Ru “Molly” Jhong, Claire E. Tornow, Chaerin Kim, Sumit Verma, Justin L. Oberst, Paul S. Anderson, Andrew A. Gewirth, Tsuyohiko Fujigaya, Naotoshi Nakashima, Paul J.A. Kenis, Gold Nanoparticles on Polymer-Wrapped Carbon Nanotubes
An Efficient and Selective Catalyst for the Electroreduction of CO2, ChemPhysChem, 10.1002/cphc.201700815, 18, 22, 3274-3279, 2017.11, 優れた電気伝導性を持つカーボンナノチューブ上に金ナノ粒子を担持することに成功し、二酸化炭素電気化学還元触媒として用いたところ、高い選択性と低い過電圧を示すことが明らかとなった。.
23. 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±0.5 nm 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 20 days 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..
24. Mohamed Mahmoud Nasef, Tsuyohiko Fujigaya, Ebrahim Abouzari-Lotf, Naotoshi Nakashima, Electrospinning of poly(vinylpyrrodine) template for formation of ZrO2 nanoclusters for enhancing properties of composite proton conducting membranes, International Journal of Polymeric Materials and Polymeric Biomaterials, 10.1080/00914037.2016.1201829, 66, 6, 289-298, 2017.04, Nanosized ZrO2 clusters were prepared by electrospinning a poly(vinylpyrrodine) (PVP)/ZrO2 mixture for calcination to remove PVP template and sizing. The morphological, chemical, structural, and thermal resistance changes during preparation stages were investigated using scanning electron microscope, energy-dispersive X-ray spectroscopy, transmission electron microscope, X-ray diffraction, and thermogravimetric analysis. The obtained ZrO2 clusters were used for preparation of nanocomposite membranes by dispersion in 2,6-pyridine polybenzimidazole (2,6-Py-PBI) matrix at 5 wt% content followed by phosphoric acid (PA) doping. The ZrO2 nanoclusters were found to be uniformly distributed in 2,6-Py-PBI/PA matrix leading to a remarkable increase in the PA doping level and proton conductivity of the obtained composite membrane..
25. Jun Yang, Tsuyohiko Fujigaya, Naotoshi Nakashima, 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 Ni x Co 3-x O 4 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-Ni x Co 3-x O 4) 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-Ni x Co 3-x O 4 demonstrates an excellent durability for both ORR and OER..
26. Yuki Nakashima, Naotoshi Nakashima, Tsuyohiko Fujigaya, 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, 近年ウェアラブルデバイスの電源として有望視されている熱電変換材料のうち、フレキシブル性に優れ、高い電気伝導率を持つカーボンナノチューブに注目が集まっている。しかし、カーボンナノチューブのような有機系材料においては大気安定なn型材料を作るのが困難であった。我々はベンズイミダゾール誘導体がカーボンナノチューブを大気安定n型化するドープ剤であることを世界に先駆けて発見した。.
27. Tsuyohiko Fujigaya, Yilei Shi, Jun Yang, Hua Li, Kohei Ito, Naotoshi Nakashima, 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, 2017.01, 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 (IrO) 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 IrO2 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 IrO2 deposited on conventional carbon black showed only a poor durability..
28. 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, 2017.01, 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 58.8mWcm-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..
29. J. Yang, F. Toshimitsu, Z. Yang, Tsuyohiko 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 π-π interactions, leading to such enhanced electrocatalytic activity and durability..
30. Tsuyohiko Fujigaya, Toward the development of highly durable polymer electrolyte fuel cell using carbon nanotube, Sen'i Gakkaishi, 73, 5, 213-214, 2017.
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 ∼3 nm Pt nanoparticles (Pt[sbnd]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..
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 μm, 0.2–0.3 mm, and 0–120°, respectively. These results showed that increasing the temperature from the conventional temperature of 80 °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 °C and 2 A/cm2, the electrolysis voltage is minimized to 1.69 V with a hydrophilic titanium mesh with an average pore diameter of 21 μm and a thickness of 0.2 mm..
33. 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 (Philadelphia), 10.1080/01496395.2016.1147468, 51, 15-16, 2492-2500, 2016.11, 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 π-π 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)..
34. H. Wenxin, N. 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.
35. Tsuyohiko Fujigaya, Shinsuke Hirata, M. R. Berber, 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.
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-cm2 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 °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 °C, pressure greater than 0.1 MPa suppresses the overvoltage, and so does pressures greater than 0.3 MPa at 130 °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..
37. 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 °C and dry condition, respectively. The membrane with 5 wt% ZrO2 also showed the highest performance in a single cell at 120 °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..
38. 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.
39. 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.
40. 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.
41. 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.
42. Tsuyohiko Fujigaya, C.R Kim, Yiki 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. Yusuke Segusa, Tsuyohiko Fujigaya, Naotoshi Nakashima, Interfacial Engineering of Epoxy/Carbon Nanotube by using Reactive Glue for Effective Reinforcement of the Composite, Polymer Journal, 2016.02.
44. 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..
45. Naoki Imazu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Fabrication of flexible transparent conductive films from long double-walled carbon nanotubes, Sci. Technol. Adv. Mater. , 10.1088/1468-6996/15/2/025005, 15, 025005, 2016.01.
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 (Pt-NPs) 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 mA mgPt
-1 for the electrocatalyst with 3 nm Pt-NPs, in which the power density reached 350 mW cm-2, which was 1.4 times higher than that of the electrocatalyst synthesized without NaOH (250 mW cm-2) at 120 °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.
48. 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.
49. Tsuyohiko Fujigaya, Hirata Shinsuke, 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, 2015.11.
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. 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.
52. 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, 2015.10.
53. 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.
54. 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.
55. 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.
56. 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..
57. 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..
58. 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..
59. 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.
60. 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 CoCp 2 @SWNTs) and revealed that the material showed a negative-type (n-type) semiconducting behaviour (Seebeck coefficient:-41.8 μV K-1 at 320 K). The CoCp 2 @SWNT film was found to show a high electrical conductivity (43,200 S m-1 at 320 K) and large power factor (75.4 μW 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 CoCp 2 @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 W m-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..
61. 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, To fabricate transparent conducting films (TCFs) for electron ic 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 Ωsq-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..
62. 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.
63. 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, 2014.11, 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 ∼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..
64. Akiyo Nagashima, Tsuyohiko Fujigaya, Naotoshi Nakashima, Effect of Nanostructure of the Electrocatalyst Based on Carbon Nanotube for the Activation Overpotential for PEFC, JOURNAL OF MATERIALS CHEMISTRY C, 10.1149/06403.0151ecst, 64, 3, 151-157, 2014.10.
65. Tsuyohiko Fujigaya, BERBER MOHAMED, Naotoshi 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, 2014.10.
66. 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.
67. Yoo JongTae, ChaeRin Kim, Tsuyohiko Fujigaya, Naotoshi Nakashima, Graphene oxide and laponite composite films with high oxygen-barrier properties, NANOSCALE, 10.1039/c4nr03429e, 6, 18, 10824-10830, 2014.09.
68. Naotoshi Nakashima, Tsuyohiko Fujigaya, Junichi Morita, Grooves of Bundled Single-Walled Carbon Nanotubes Dramatically Enhance the Reactivity of Oxygen Reduction Reaction, ChemCatChem, 10.1002/cctc.201402565, 6, 11, 3169-3173, 2014.09.
69. Hafez Inas H, BERBER MOHAMED, 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.
70. 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.
71. 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.
72. JongTae Yoo, ChaeRin Kim, Tsuyohiko Fujigaya, Naotoshi Nakashima, 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, 2014.07.
73. Takao Sada, Tsuyohiko Fujigaya, Naotoshi Nakashima, Design and fabrication of Ni nanowires having periodically hollow nanostructures, NANOSCALE, 10.1039/c4nr02625j, 6, 19, 11484-11488, 2014.05.
74. 藤ヶ谷 剛彦, 金 菜リン, 松本 和也, 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.
75. Takahiro Fukumaru, Fumiyuki Toshimitsu, Tsuyohiko Fujigaya, Naotoshi Nakashima, Effects of the chemical structure of polyfluorene on selective extraction of semiconducting singlewalled carbon nanotubes, Nanoscale, 10.1039/c4nr00809j, 6, 5879 -5886, 2014.03.
76. BERBER MOHAMED, 藤ヶ谷 剛彦, 中嶋 直敏, 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.
77. 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, 10.15261/serdj.21.37, 21, 1, 37-45, 2014, 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 crosslinking 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..
78. 堤 優介, 藤ヶ谷 剛彦, 中嶋 直敏, 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.
79. Takahiro Fukumaru, Tsuyohiko Fujigaya, Naotoshi Nakashima, Fabrication of Poly(p-phenylene benzobisoxazole) Film Using a Soluble Poly(o-alkoxyphenyl amide) as the Precursor, Macromolecules, 4, 6318-6323, 2013.11.
80. 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..
81. 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.
82. Jongtae Yoo, Tsuyohiko Fujigaya, Naotoshi Nakashima, Molecular recognition at the nanoscale interface within carbon nanotube bundles, Nanoscale, 10.1039/c3nr01828h, 5, 16, 7419-7424, 2013.08, 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..
83. 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..
84. 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, 2013.06, Low durability of polymer electrolyte fuel cell (PEFC) is a major drawback that should be solved. Recent 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 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..
85. 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.
86. 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..
87. 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) (SPTES) and poly(2,2′-benzidinedisulfonicacid)-alt-(1,4,5,8- naphthalenetetracarboxylic dianhydride) (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 thaTmWNT/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..
88. 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 °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..
89. 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..
90. 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..
91. 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..
92. 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 μm in width and 100 μm 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..
93. 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..
94. 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, 2012.07, 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..
95. 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°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°C in flowing N 2, which is the highest temperature among the organic polymers reported so far..
96. 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, 2012.02, 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)..
97. 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 and 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..
98. Hiroaki Ozawa, Tsuyohiko 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. The selective recognition/extraction behavior of single-walled carbon nanotubes (SWNTs) with specific chirality was investigated using a poly(dihydrophenanthrene), whose chemical structure is different in the non-aromatic ring numbers from that of poly(fluorenes)..
99. 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 3.2nm, 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. Take the tube: Selective solubilization of semiconducting single-walled carbon nanotubes (SWNTs) was achieved by wrapping them in a fluorene-carbazole copolymer. The extracted (7,6)- and (8,7)SWNTs were modified by metal nanoparticles (NPs) to fabricate metal NP/copolymer/semiconducting SWNT nanohybrids (see figure)..
100. 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..
101. 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.
102. 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..
103. 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 PART 1, 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..
104. 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..
105. 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 ∼105. The transport properties of the TFT changed after coordination of the AuNPs with the SWNTs/copolymer 1..
106. Tsuyohiko Fujigaya, Naotoshi Nakashima, Design and developments of carbon nanotube composite materials, kobunshi, 60, 7, 453-456, 2011.07, 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..
107. 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, 2011.07, 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..
108. 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 PART 1, 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..
109. 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 ∼ pyrene < triphenylene < p-terphenyl < tetraphene < tetracene..
110. 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, 2011.06, Asimple 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..
111. Takao Sada, Tsuyohiko Fujigaya, Yasuro Niidome, Kohji Nakazawa, Naotoshi Nakashima, Near-IR laser-triggered target cell collection using a carbon nanotube-based 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 μm 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..
112. 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, 2011.04, We describe the finding that copolymers having a longdouble 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 visnear IR spectroscopies. We also carried out molecular mechanical simulations to understand the difference in the chiral selective solubilization behavior..
113. 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, 2011.03, 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..
114. 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 Ni0-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..
115. 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 alter-native 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..
116. 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 μm. 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..
117. 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, 2011.02, We now describe the finding that a copolymer of 9,9-dioctylfluorenyl-2,7- diyl and bipyridine (BPy) can extract in "onepot" ≈ 9697%- enriched (6,5)-SWNTs in m-xylene and p-xylene not containing metallic SWNTs, which was revealed by visnear IR absorption, photoluminescence, and Raman spectroscopies..
118. 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, 2011.01, 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 °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..
119. 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., ∼120 δ/sq), and a small average surface roughness (i.e., ∼3.5 nm for a displayed 10×10 μm 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" for many applications..
120. 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..
121. 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 nonhumid atmosphere using solubilized CNTs as material..
122. 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..
123. 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..
124. 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 any 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%)..
125. 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..
126. 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, 3610-3614, 2008.10, A study was conducted to propose the utilization of single-walled carbon nanotubes (SWCNT) as a photon antenna that serves as an effective molecular heater around the near-infrared (NIR) region. The study demonstrates that SWCNTs are nanomaterials that possess significant electrical, mechanical,and thermal properties. It was also shown that characteristic absorption bands in the NIR region are formed, due to the interband transition between the mirror-image spikes in the density of states of the SWCNTs. It was also demonstrated that these SWCNTs can be used as molecular heaters through photothermal conversion phenomena that occur due to a nonradiative process of excited SWCNT by NIR irradiation. The results indicate that the SWCNTs in the composite gel remain structurally intact, without formation of outflow of SWCNTs from the gel..
127. 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..
128. Tsuyohiko Fujigaya, Shinsuke Haraguchi, Takahiro Fukumaru, Naotoshi Nakashima, Development of novel carbon nanotube/photopolymer nanocomposites with high conductivity and their application to nanoimprint photolithography, Advanced Materials, 10.1002/adma.200701780, 20, 11, 2151-2155, 2008.06, The fabrication of CNT/polymer composites by in-situ solvent-free photo-polymerization using a UV-curable monomer and the structural and electrical properties of the films obtained by UV curing of the composites was described. The fabrication of submicrometer-ordered two-dimensional patterns by employing the nanoimprint photolithography technique was also described. Photopolymerization results in a decrease in the intensity of absorption bands, indicating that the polymerization reaction occurs in the presence of the SWNTs. It is also seen that the polymer films consist of a mixture of isolated and small-bundled SWNTs, similar to surfactant-assisted dispersion of SWNTs. The sizes of the aggregates is found to be 200-300 nm, which is in good agreement with the result of the absence of visible macroscopic-sized aggregates in the nanocompaoites..
129. 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, Polybenzimidazole (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 π-π interaction between the PBI and the sidewalls of the SWNTs..
130. 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 HiPcoSWNTs, and (6,5) and (7,5) for CoMoCAT-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..
131. 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..
132. 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..
133. 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, 2535-2539, 2007.09, It is reported that the self-assembly of single-walled carbon nanotubes with a honey comb structures is spontaneous on solid substrates by simple solution casting of a SWNT-lipid conjugate (complex-1). The optical microscopic observations of the films cast from complex-1 was conducted in dichloromethane, chloroform, and toluene in air at 48-90% relative humidity (RH). The assembled microporous structures were formed from concentrations over 0.5 mg mL -1 at greater than 63% RH. The higher RH led to the formation of micropores with large diameters, while the size of micropores decreased with the increasing concentration of complex 1. The solvents with higher boiling temperatures produced micropores with large diameters, determining the importance of the evaporating speed. The results of experiment show that the honeycomb structures of SWNT are successfully formed from a simple solution casting process at higher RH using a s-SWNT-lipid conjugate as the material..
134. Tsuyohiko Fujigaya, Naotoshi Nakashima, Solubilization of carbon nanotubes and their applications, KOBUNSHI RONBUNSHU, 10.1295/koron.64.539, 64, 9, 539-552, 2007.09, Because of the insolubility of carbon nanotubes (CNTs), chemical, biochemical, biological and medical applications using these materials have been rather limited. Soluble carbon nanotubes are of interest as nanomaterials in such fields. In this comprehensive paper, we describe i) strategies for the individual solubilization of CNT, especially for single-walled carbon nanotubes (SWNTs) in water or organic solvents and ii) the fundamental applications of the solubilized CNT..
135. 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..
136. Jae Won Jang, Daniel Maspoch, Tsuyohiko 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..
137. 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, 2007.01, 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 thermoreversible 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..
138. Seung Woo Lee, Byung Keun Oh, Raymond G. Sanedrin, Khalid Salaita, Tsuyohiko Fujigaya, Chad A. Mirkin, Biologically active protein nanoarrays generated using parallel dip-pen nanolithography, Advanced Materials, 10.1002/adma.200600070, 18, 9, 1133-1136, 2006.05, The generation of biologically active protein nanoarrays using parallel dip-pen nanolithography (DPN), was investigated. To generate nanoscale arrays of amine-reactive dot features on a gold substrate, which was prepared using a 26-pen array was coated with NHSC11SH by immersing it in a 10mM NHSC11SH acetonitrile solution for 10 s. The DPN-generated NHSC 11SH dot arrays served as a template for the immobilization of protein A/G. Through the use of the affinity binding of the antibodies on protein A/G, biologically active antibody nanoarrays can e generated over macroscopic distances through parallel DPN, demonstrating the versatility of this approach for making similar antibody structures in a relatively high-throughput manner. The results show that researchers in nanoscience and biology will consider new ways of using such patterned interfaces to probe biological systems..
139. Tsuyohiko Fujigaya, Dong Lin Jiang, Takuzo 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 number = 0-2) were found to react with (MeSO 3)2Fe to form dendritic coordination polymers ([Fe(Gntrz)3]-(MeSO3)2·2H2O) 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 (Dp = 20 → 10 → 3) and spin-crossover temperature (Tc = 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 C 3v symmetric array of medium-sized (G1trz)-Fe..
140. Tsuyohiko Fujigaya, Dong Lin Jiang, Takuzo 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..
141. Tsuyohiko Fujigaya, Yuji Sibasaki, Shinji Ando, Shinji Kishimura, Masayoshi Endo, Masaru Sasago, Mitsuru 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 = 2.1μm-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-HFISt60)] prepared by free radical copolymerization of VSF and HFIST showed good transparency (OD = 2.4μm-1) as well. Poly(VSF40-co-HFISt22-co-tert-butoxycarbonyl HFISt38) (OD = 2.8μm-1) was prepared from poly(VSF40-co-HFISt60) and di-tert-butyl dicarbonate in the presence of 4-(dimethylamino)pyridine (DMAP). A resist film consisting of poly(VSF40-co-HFISt22-co-tert-Boc HFISt38) 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 °C for 1 min was exposed to 157-nm laser, postbaked at 130 °C for 1 min, and developed with a 2.38 wt % tetramethylammonium hydroxide (TMAH) aqueous solution..
142. Insik In, Hyosan Lee, Tsuyohiko Fujigaya, Masaki Okazaki, Mitsuru Ueda, Sang Youl 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 AB2 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/cm2 and the contrast of 1.6 when it was exposed to 365 nm light and postbaked at 120°C, followed by developing with 0.5 wt% aqueous TMAH solution at room temperature. The heat-treated (300°C, 30 min) negative image did not show any distortion..
143. Shinji Ando, Tsuyohiko Fujigaya, Mitsuru 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, 2 A, 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 F2 lithography (157 nm)..
144. 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 μm-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 μm-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 sulfonate40-co-HFISt60) [poly(VSO3iPr6F40-co-HFISt60)] was found to be 2.4 μm-1 at 157 nm. The photoresist consisting of partially t-BOC-protected poly(VSO3iPr6F40-co-HFISt28-co-t-BOCHFISt32) (Abs. 2.6) and an photoacid generator showed the contrast and sensitivity of 10.3 and 5.0 mJ cm-2, respectively..
145. Kwon Young-Gil, Jin Baek Kim, Tsuyohiko Fujigaya, Yuji Shibasaki, Mitsuru 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, 2002.01, A positive working low-molecular-weight photoresist based on partially t-Boc protected tetra-Cmethylcalix[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°C 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 μm 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..
146. Shinji Ando, Tsuyohiko Fujigaya, Mitsuru 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, 2002.01, 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 F2 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..
147. 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, 2001.01, 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..
148. 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, 2000.01, 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..