Faculty Profiles - TOKUNAGA, Tomoharu

Blue photoluminescence at room temperature from Y<inf>2</inf>O<inf>3</inf>-doped ZrO<inf>2</inf> polycrystals sintered by flash sintering

Yudai Yamashita, Asa Itoh, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

Applied Physics Express Vol. 13 ( 3 ) 2020.3

Language：Japanese Publishing type：Research paper (scientific journal)

© 2020 The Japan Society of Applied Physics. Photoluminescence band variation of Y2O3-doped ZrO2 (YSZ) polycrystals was investigated for flash-sintered YSZ polycrystals. Nearly full density could be obtained by flash sintering under an alternating current field of 100 V cm-1, 100 Hz, limiting current of 1000 mA and at 1200 °C for 5 min. The flash-sintered YSZ polycrystals emitted blue photoluminescence even at room temperature under excitation of a handheld ultraviolet light, which could be observed with the naked eye. By contrast, conventionally sintered YSZ polycrystals emitted no photoluminescence despite using the same raw powders. In addition, the photoluminescence bands were tunable by varying the Y2O3 content.

DOI： 10.35848/1882-0786/ab7710

Green Synthesis of Size-Tunable Iron Oxides and Iron Nanoparticles in a Salt Matrix Reviewed

Mai Thanh Nguyen, Kai Yu, Tomoharu Tokunaga, Kornkit Boonyaperm, Soorathep Kheawhom, Masashi Arita, Tetsu Yonezawa

ACS SUSTAINABLE CHEMISTRY & ENGINEERING Vol. 7 ( 21 ) page： 17697 - 17705 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

This research is devoted for the synthesis of Fe oxide and Fe nanoparticles (NPs) via, respectively, thermal decomposition of iron(III) oleate and H-2 reduction of either iron(III) oleate or iron oxide NPs in a NaCl matrix. Lowering the weight ratios of metal precursor to NaCl and synthesis temperature results in smaller particle sizes. A higher uniformity of Fe NPs can be achieved with a two-step synthesis, that is, thermal decomposition of iron oleate followed by H-2 reduction of iron oxides, with the milling of iron oxides and NaCl prior to the reduction step. Fe NPs obtained in this study are stable in the air for long-time storage. It is found that thin oxide and C layers on the particle surface are responsible for their stability.

DOI： 10.1021/acssuschemeng.9b03950

Technique to control specimen electric current during a flash state with alternating current electric fields Reviewed

Yudai Yamashita, Tsuyoshi Kurachi, Tomoharu Tokunaga, Hidehiro Yoshida, Takahisa Yamamoto

JOURNAL OF THE CERAMIC SOCIETY OF JAPAN Vol. 127 ( 11 ) page： 849 - 851 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI

A simple technique to control the specimen electric current during flash sintering was developed using AC electric fields in 3 mol% Y2O3-doped ZrO2. Flash sintering is characterized by the occurrence of a flash event, i.e., a spike in the specimen electric current, which makes it difficult to control the specimen electric current at/after the flash event for AC electric fields. However, AC electric fields are very attractive from the viewpoint of a suppression of the severe reduction arising from the unidirectional ionic flow during the flash event, which is a fatal phenomenon with DC electric fields. In this study, we develop a simple technique to control the AC electric fields at/after the flash event by limiting the AC electric fields under certain values. As a result, the flash state after the flash event is successfully maintained. Further, it is found that 3 mot% Y2O3-doped ZrO2 compacts prepared by DC- and AC-flash sintering emit blue fluorescence (FL) under 254 nm ultraviolet tight. The blue FL is not obtained in the compacts prepared by conventionally-sintering. The application of electric fields is confirmed to result in the blue florescent properties of 3 mot% Y2O3-doped ZrO2 compacts. (C) 2019 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.19144

One-minute Joule Annealing Enhances the Thermoelectric Properties of Carbon Nanotube Yarns via the Formation of Graphene at the Interface Reviewed

Masaki Hada, Taisuke Hasegawa, Hirotaka Inoue, Makito Takagi, Kazuki Omoto, Daiki Chujo, Shogo Iemoto, Taihei Kuroda, Taiga Morimoto, Takuma Hayashi, Toru Iijima, Tomoharu Tokunaga, Naoshi Ikeda, Kazuhiro Fujimori, Chihiro Itoh, Takeshi Nishikawa, Yoshifumi Yamashita, Toshihiko Kiwa, Shin-ya Koshihara, Satoshi Maeda, Yasuhiko Hayashi

ACS Appl. Energy Mater. Vol. 2 ( 10 ) page： 7700 - 7708 2019.10

Selective Reduction Mechanism of Graphene Oxide Driven by the Photon Mode versus the Thermal Mode. Reviewed International journal

Masaki Hada, Kiyoshi Miyata, Satoshi Ohmura, Yusuke Arashida, Kohei Ichiyanagi, Ikufumi Katayama, Takayuki Suzuki, Wang Chen, Shota Mizote, Takayoshi Sawa, Takayoshi Yokoya, Toshio Seki, Jiro Matsuo, Tomoharu Tokunaga, Chihiro Itoh, Kenji Tsuruta, Ryo Fukaya, Shunsuke Nozawa, Shin-Ichi Adachi, Jun Takeda, Ken Onda, Shin-Ya Koshihara, Yasuhiko Hayashi, Yuta Nishina

ACS nano Vol. 13 ( 9 ) page： 10103 - 10112 2019.9

Language：English Publishing type：Research paper (scientific journal)

A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final materials or devices. Therefore, an understanding of the mechanisms of GO reduction is important for controlling the properties of functional two-dimensional systems. Here, we determined the average structure of reduced GO prepared via heating and photoexcitation and clearly distinguished their reduction mechanisms using ultrafast time-resolved electron diffraction, time-resolved infrared vibrational spectroscopy, and time-dependent density functional theory calculations. The oxygen atoms of epoxy groups are selectively removed from the basal plane of GO by photoexcitation (photon mode), in stark contrast to the behavior observed for the thermal reduction of hydroxyl and epoxy groups (thermal mode). The difference originates from the selective excitation of epoxy bonds via an electronic transition due to their antibonding character. This work will enable the preparation of the optimum GO for the intended applications and expands the application scope of two-dimensional systems.

DOI： 10.1021/acsnano.9b03060

Porous ZnV2O4 Nanowire for Stable and High-Rate Lithium-Ion Battery Anodes Reviewed

Lyn Marie, Z. De Juan-Corpuz, Mai Thanh Nguyen, Ryan D. Corpuz, Tetsu Yonezawa, Nataly Carolina Rosero-Navarro, Kiyoharu Tadanaga, Tomoharu Tokunaga, Soorathep Kheawhom

ACS Applied Nano Materials Vol. 2 ( 7 ) page： 4247 - 4256 2019.7

Preparation and Growth Mechanism of Pt/Cu Alloy Nanoparticles by Sputter Deposition onto a Liquid Polymer. Reviewed International journal

Lianlian Deng, Mai Thanh Nguyen, Shuang Mei, Tomoharu Tokunaga, Masaki Kudo, Syo Matsumura, Tetsu Yonezawa

Langmuir : the ACS journal of surfaces and colloids Vol. 35 ( 25 ) page： 8418 - 8427 2019.6

Language：English

We use a green sputtering technique to deposit a Pt/Cu alloy target on liquid polyethylene glycol (PEG) to obtain well-dispersed and stable Pt29Cu71 alloy nanoparticles (NPs). The effects of sputtering current, rotation speed of the stirrer, sputtering time, sputtering period, and temperature of PEG on the particle size are studied systematically. Our key results demonstrate that the aggregation and growth of Pt/Cu alloy NPs occurred at the surface as well as inside the liquid polymer after the particles landed on the liquid surface. According to particle size analysis, a low sputtering current, high rotation speed for the stirrer, short sputtering period, and short sputtering time are found to be favorable for producing small-sized single crystalline alloy NPs. On the other hand, varying the temperature of the liquid PEG does not have any significant impact on the particle size. Thus, our findings shed light on controlling NP growth using the newly developed green sputtering deposition technique.

DOI： 10.1021/acs.langmuir.9b01112

Size-Tunable Alumina-Encapsulated Sn-Based Phase Change Materials for Thermal Energy Storage Reviewed

Shilei Zhu, Mai Thanh Nguyen, Tomoharu Tokunaga, Tetsu Yonezawa

ACS APPLIED NANO MATERIALS Vol. 2 ( 6 ) page： 3752 - 3760 2019.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

The most commonly used phase change materials (PCMs), like organic compounds and inorganic salts, were limited in application by their low thermal conductivity. Herein, for the first time, alumina-encapsulated metallic Sn-based PCMs, named Sn@Al2O3, were successfully fabricated with tunable size (60-2000 nm) by a facile process from low-cost chemicals. The robust fabrication process consists of a surfactant-free solvothermal synthesis of SnO2 spheres, boehmite treatment on SnO2 spheres, calcination in the air, and the final hydrogen reduction to transform SnO2 to metallic Sn, endowing the PCMs with high potential for mass production. The as-obtained Sn@Al2O3 showed a core-shell structure, in which a main metallic Sn core located in the center covered with an Al2O3 shell with small Sn nanoparticles distributed inside. The boehmite treatment, in which the penetration of aluminum species into SnO2 spheres played an important role, was found to be responsible for the unique structure formation of final Sn@Al2O3. The understanding of structure formation mechanism gives the possibilities of a new facile way for the synthesis of metal nanoparticles and particle-distributed nanostructures. The obtained Sn@Al2O3 particles not only have high PCM content (92.37 wt %) but also show a stable thermal behavior and morphology during 100 melt freeze cycles in the air atmosphere. Furthermore, the low melting temperature of the PCM core, combined with high thermal conductivity of both core material (Sn, 66.8 W m(-1) K-1) and shell material (Al2O3, 35 W m(-1) K-1), makes Sn@Al2O3 potentially suitable for rapid thermal energy storage in the range 100-300 degrees C.

DOI： 10.1021/acsanm.9b00649

Topologically immobilized catalysis centre for long-term stable carbon dioxide reforming of methane Reviewed International journal

Shusaku Shoji, Xiaobo Peng, Tsubasa Imai, Paskalis Sahaya Murphin Kumar, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Shigenori Ueda, Ayako Hashimoto, Noritatsu Tsubaki, Masahiro Miyauchi, Takeshi Fujita, Hideki Abe

CHEMICAL SCIENCE Vol. 10 ( 13 ) page： 3701 - 3705 2019.4

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Methane reforming at low temperatures is of growing importance to mitigate the environmental impact of the production of synthesis gas, but it suffers from short catalyst lifetimes due to the severe deposition of carbon byproducts. Herein, we introduce a new class of topology-tailored catalyst in which tens-of-nanometer-thick fibrous networks of Ni metal and oxygen-deficient Y2O3 are entangled with each other to form a rooted structure, i.e., Ni#Y2O3. We demonstrate that the rooted Ni#Y2O3 catalyst stably promotes the carbon-dioxide reforming of methane at 723 K for over 1000 h, where the performance of traditional supported catalysts such as Ni/Y2O3 diminishes within 100 h due to the precluded mass transport by accumulated carbon byproducts. In situ TEM demonstrates that the supported Ni nanoparticles are readily detached from the support surface in the reaction atmosphere, and migrate around to result in widespread accumulation of the carbon byproducts. The long-term stable methane reforming over the rooted catalyst is ultimately attributed to the topologically immobilized Ni catalysis centre and the synergistic function of the oxygen-deficient Y2O3 matrix, which successfully inhibits the accumulation of byproducts.

DOI： 10.1039/c8sc04965c

Nanoporous Nickel Composite Catalyst for the Dry Reforming of Methane. Reviewed International journal

Takeshi Fujita, Xiaobo Peng, Akira Yamaguchi, Yohei Cho, Yongzheng Zhang, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Masahiro Miyauchi, Hideki Abe

ACS omega Vol. 3 ( 12 ) page： 16651 - 16657 2018.12

Language：English

The development of efficient catalysts with high activities and durabilities for use in the dry reforming of methane (DRM) is desirable but challenging. We report the development of a nanoporous nickel composite (nanoporous Ni/Y2O3) via a facile one-step dealloying technique, for use in the DRM. Focusing on the low-temperature DRM, our composite possessed remarkable activity and durability against coking compared with conventional particle-based Ni catalysts. This was attributed to the aluminum oxides present on the Ni surface, which suppress pore coarsening. In addition, the inert bundled Y2O3 nanowires are suitable for use as substrates for nanoporous Ni.

DOI： 10.1021/acsomega.8b02023

Intergranular amorphous films formed by DC electric field in pure zirconia Reviewed

Nobuhiro Morisaki, Hidehiro Yoshida, Tetsuro Kobayashi, Tomoharu Tokunaga, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 101 ( 8 ) page： 3282 - 3287 2018.8

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

It is difficult to obtain pure ZrO2 sintered compacts with a bulk style at room temperature because a large volumetric expansion from tetragonal to monoclinic phase (t/m) transformation occurs at around 1000 degrees C, which is lower than the sintering temperature. In contrast, pure monoclinic ZrO2 can be consolidated without shattering using flash-sintering at 1350 degrees C for 5minutes under an applied DC electric field of 175V/cm. High-resolution transmission electron microscopy and electron energy loss spectroscopy have revealed that amorphous films are formed along grain boundaries after flash-sintering at 1350 degrees C for 5minutes. Monoclinic ZrO2 flash-sintered compact including the amorphous films are able to survive without shattering through the t/m transformation, as the amorphous films partially absorb the large volumetric expansion arising from the t/m transformation. The formation of the amorphous films results from the severe reducing condition due to the applied DC electric fields during flash-sintering.

DOI： 10.1111/jace.15485

Ligand free green plasma-in-liquid synthesis of Au/Ag alloy nanoparticles Reviewed

David Čempel, Mai Thanh Nguyen, Yohei Ishida, Tomoharu Tokunaga, Tetsu Yonezawa

New Journal of Chemistry Vol. 42 ( 8 ) page： 5681 - U9 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：Royal Society of Chemistry

Au/Ag alloy nanoparticles (NPs) were successfully prepared by a one step synthesis using HAuCl4 and [Ag(NH3)2]+ as the corresponding precursors in a microwave-induced plasma in liquid process (MWPLP) without the addition of any organic protecting or reducing agents. The time dependent reduction and particle formation during the 140 min plasma discharge were studied with TEM, UV-vis extinction spectra, and ICP-OES. After 140 min, the HAADF-STEM and EDX results indicated that the obtained Au/Ag NPs were alloy NPs. Varying the input molar ratios of the metal precursors allowed for control of the composition of the Au/Ag alloy NPs.

DOI： 10.1039/c7nj05154a

Sputter Deposition toward Short Cationic Thiolated Fluorescent Gold Nanoclusters: Investigation of Their Unique Structural and Photophysical Characteristics Using High-Performance Liquid Chromatography Reviewed International journal

Yohei Ishida, Akihiro Morita, Tomoharu Tokunaga, Tetsu Yonezawa

LANGMUIR Vol. 34 ( 13 ) page： 4024 - 4030 2018.4

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

We herein present the preparation of short, bulky cationic thiolate (thiocholine)-protected fluorescent Au nanoclusters via sputter deposition over a liquid polymer matrix. The obtained Au nanoclusters showed near-infrared fluorescence and had an average core diameter of 1.7 +/- 0.6 nm, which is too large compared to that of the reported fluorescent Au nanoclusters prepared via chemical means. We revealed the mechanism of formation of this unique material using single particle electron microscopy, optical measurements, X-ray photoelectron spectroscopy (XPS), and high-performance liquid chromatography fractionations. The noncrystallized image was observed via single-particle high-angle annular dark-field scanning transmission electron microscopy observations and compared with chemically synthesized crystalline Au nanoparticle with the same diameter, which demonstrated the unique structural characteristic speculated via XPS. The size fractionation and size-dependent fluorescence measurement, together with other observations, indicated that the nanoclusters most probably contained a mixture of very small fluorescent species in their aggregated form and were derived from the sputtering process itself and not from the interaction between thiol ligands.

DOI： 10.1021/acs.langmuir.8b00067

Au/Cu Bimetallic Nanoparticles via Double-Target Sputtering onto a Liquid Polymer Reviewed International journal

Mai Thanh Nguyen, Hong Zhang, Lianlian Deng, Tomoharu Tokunaga, Tetsu Yonezawa

LANGMUIR Vol. 33 ( 43 ) page： 12389 - 12397 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

Alloy nanoparticles (NPs) of a bimetal system, Au/Cu, that form intermetallic compounds in a bulk state have been successfully produced using a double-target sputtering technique onto a low-cost and biocompatible liquid polymer (polyethylene glycol, PEG). The formation of an Au/Cu solid solution alloy in individual NPs was revealed by scanning transmission electron microscopy-energy-dispersive X-ray elemental mapping analysis. Altering the sputter currents for Au and Cu targets resulted in a tailored NP composition, but the particle sizes did not significantly vary. We found similar structures, sizes, and optical properties of Au/Cu NPs obtained by double-head sputtering on carbon-coated transmission electron microscopy grids or PEG and by Au/Cu alloy target sputtering. Random alloy formation occurred in matrix sputtering using double-target heads. This method is advantageous for manipulating the alloy composition through highly independent control of sputter parameters for each metal target.

DOI： 10.1021/acs.langmuir.7b03194

In-Situ TEM Study of a Nanoporous Ni-Co Catalyst Used for the Dry Reforming of Methane Reviewed

Takeshi Fujita, Kimitaka Higuchi, Yuta Yamamoto, Tomoharu Tokunaga, Shigeo Arai, Hideki Abe

METALS Vol. 7 ( 10 ) page： 406 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：MDPI AG

We performed in-situ transmission electron microscopy (TEM) on a dealloyed nanoporous NiCo catalyst used for the dry reforming of methane (DRM) to investigate the origin of the catalytic activity and structural durability. The in-situ observations and local chemical analysis indicated that the DRM induced chemical demixing of Ni and Co accompanied by grain refinement, implying possible synergic effects in a general bimetallic NiCo catalyst when used for the DRM.

DOI： 10.3390/met7100406

Consolidation of undoped, monoclinic zirconia polycrystals by flash sintering Reviewed

Nobuhiro Morisaki, Hidehiro Yoshida, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 100 ( 9 ) page： 3851 - 3857 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

Consolidated, monoclinic ZrO2 polycrystal was produced from undoped ZrO2 powders in air by flash sintering at the sintering temperature of 1350 degrees C for 5minutes or 3hours under an applied DC electric field of 175V/cm. When the ZrO2 was heated under the applied DC field, the electric current of the specimen steeply increased at the furnace temperature of 1335 degrees C below the sintering temperature of 1350 degrees C. When the furnace temperature was decreased from the sintering temperature of 1350 degrees C to room temperature, volumetric expansion associated with tetragonal-to-monoclinic phase transformation gradually took place at the furnace temperature from 1000 degrees C to 750 degrees C, and monoclinic ZrO2 body was remained consolidated even at room temperature in both specimens. In contrast, conventionally sintered ZrO2 without applying DC field exhibited the abrupt volumetric expansion at about 1000 degrees C, and shattered. SEM observation revealed the presence of grain-boundary second phase in the flash-sintered specimen for 3hours, which is a possible origin of keeping a bulk body at room temperature. The thinner second phase is considered to be formed also in the flash-sintered specimen for 5minutes, although the formation of the phase could not be observed clearly by SEM observation. On the other hand, XRD measurements showed that <001> directions of the monoclinic ZrO2 grains were oriented along the applied DC field after the isothermal flash sintering for 3hours while the grain alignment could not be observed in flash-sintered specimen for 5minutes. The alignment of ZrO2 grains observed in the isothermal flash sintering is considered to be closely related to the preferential direction of oxygen ionic conduction and the second phase formed along grain boundaries.

DOI： 10.1111/jace.14954

Electric current-controlled synthesis of BaTiO3 Reviewed

Yu Nakagawa, Hidehiro Yoshida, Akinori Uehashi, Tomoharu Tokunaga, Katsuhiro Sasaki, Takahisa Yamamoto

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Vol. 100 ( 9 ) page： 3843 - 3850 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY

In BaTiO3, flash-sintering associated with a surge of the specimen electric current sometimes results in an inhomogeneous microstructure including Ti-excess secondary phases because of discharging. We applied field-assisted sintering technique (FAST) under precisely controlled specimen current that was set just below the threshold value for the occurrence of flash event for BaTiO3, to avoid the occurrence of the discharging. As a result, uniform and fine-grained compacts were obtained without any secondary phases. A relative density of approximately 92% was achieved under FAST condition of 100 V/cm with a limiting current of 72 mA and soaking time of 3 hours at 1070 degrees C. The voltages during sintering under a constant current of 72 mA were found to decrease during the soaking process. Electron energy loss spectroscopy revealed the generation of excess oxygen vacancies at/near grain boundaries. The excess oxygen vacancies induced by application of DC electric fields were confirmed to reduce the voltages and to retard the shrinkage rate in a final sintering stage.

DOI： 10.1111/jace.14938

Structural Control Parameters for Formation of Single-Crystalline ss-Sn Nanorods in Organic Phase Reviewed

Lyn Marie Z. De Juan, Mai Thanh Nguyen, Tetsu Yonezawa, Tomoharu Tokunaga, Hiroki Tsukamoto, Yohei Ishida

CRYSTAL GROWTH & DESIGN Vol. 17 ( 9 ) page： 4554 - 4562 2017.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CHEMICAL SOC

For the first time, investigation on the effect of lowering the synthesis temperature below room temperature (10 to -10 degrees C) and increasing the viscosity of the reaction solution at certain temperatures has been used to trigger the formation of single-crystalline ss-Sn nanorods (NRs) in a chemical synthesis using an organic solvent. These two parameters govern the energy of the particles in the solution, thereby mediating the selective attachment to the nuclei and the preferential growth of Sn along the c-axis. The length and aspect ratio of the NRs were inversely proportional to the synthesis temperature and directly proportional to the viscosity of the reaction solution. In addition, we found that poly(vinylpyrrolidone) with a high molecular weight aided the formation of longer and higher aspect ratio NRs via the bridge flocculation effect.

DOI： 10.1021/acs.cgd.7b00227

Water transport phenomena through membranes consisting of vertically-aligned double-walled carbon nanotube array

Hidetoshi Matsumoto, Shuji Tsuruoka, Yasuhiko Hayashi, Koji Abe, Kenjiro Hata, Shaoling Zhang, Yoshitaka Saito, Motohiro Aiba, Tomoharu Tokunaga, Toru Iijima, Takuma Hayashi, Hirotaka Inoue, Gehan A. J. Amaratunga

CARBON Vol. 120 page： 358 - 365 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Nanofluidics in CNTs is argumentative though it is theoretically calculated by various reports. It is because only a few of experimental reports are available, and the measured permeability is not so large as that suggested from the theoretical calculations. Also, water motion suppression in the confined space has not been exhibited by flux measurement. The present work explores these yet-unsolved discrepancies using the measurable size membrane of vertically aligned double-walled carbon nanotube array, which is borne with durability and flexibility, and a conventional measurement method is applied to the membranes. Water motion suppression occurs in the CNT confined space significantly, depending on temperature. Additionally, it is confirmed that the obtained permeability correlates to the reported experimental results with regard to the relationship between CNT length and permeability, and the correlation does not agree with permeability calculated from the Hagen-Poiseuille law. These results pose an insight into the inherent water transport characteristics in the CNT confined space. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2017.05.034