Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Nano-Assembled Thin Films of Tetraphenylporphyrin on Amine Silane-Modified Substrate for the Optical Gas Sensor

Tipplook, M; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 667 - 674 2018.5

The Nano-Structure and Their Properties of Exfoliation Several Layers-Stacked Graphene Prepared from Graphite Dispersed in Aqueous Solutions by Solution Plasma

Chae, S; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 784 - 789 2018.5

The Initial Reactions from Pyridine to Hetero-Carbon Nanomaterials Through Solution Plasma

Kim, K; Hashimi, K; Bratescu, MA; Saito, N

NANOSCIENCE AND NANOTECHNOLOGY LETTERS Vol. 10 ( 5-6 ) page： 814 - 819 2018.5

Photoinduced glycerol oxidation over plasmonic au and aum (M = Pt, Pd and Bi) nanoparticle-decorated TiO<inf>2</inf> photocatalysts Open Access

Jedsukontorn T., Saito N., Hunsom M.

Nanomaterials Vol. 8 ( 4 ) 2018.4

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

In this study, sol-immobilization was used to prepare gold nanoparticle (Au NP)-decorated titanium dioxide (TiO2) photocatalysts at different Au weight % (wt. %) loading (Aux/TiO2, where x is the Au wt. %) and Au–M NP-decorated TiO2 photocatalysts (Au3M3/TiO2), where M is bismuth (Bi), platinum (Pt) or palladium (Pd) at 3 wt. %. The Aux/TiO2 photocatalysts exhibited a stronger visible light absorption than the parent TiO2 due to the localized surface plasmon resonance effect. Increasing the Au content from 1 wt. % to 7 wt. % led to increased visible light absorption due to the increasing presence of defective structures that were capable of enhancing the photocatalytic activity of the as-prepared catalyst. The addition of Pt and Pd coupled with the Au3/TiO2 to form Au3M3/TiO2 improved the photocatalytic activity of the Au3/TiO2 photocatalyst by maximizing their light-absorption property. The Au3/TiO2, Au3Pt3/TiO2 and Au3Pd3/TiO2 photocatalysts promoted the formation of glyceraldehyde from glycerol as the principle product, while Au3Bi3/TiO2 facilitated glycolaldehyde formation as the major product. Among all the prepared photocatalysts, Au3Pd3/TiO2 exhibited the highest photocatalytic activity with a 98.75% glycerol conversion at 24 h of reaction time.

DOI： 10.3390/nano8040269

Accelerated formation of nanocarbons in solution plasma using benzene substituted with CF<inf>3</inf> group

Panomsuwan G., Li O.L., Saito N., Ishizaki T.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Nanocarbons were synthesized by a solution plasma method using benzene (C6H6) and benzotrifluoride (C5H5CF3) as precursors. The effects of the substituted CF3 group on the overall properties of synthesized nanocarbons were investigated and discussed. As determined from the characterization results, the nanocarbons obtained from both benzene and benzotrifluoride mainly exhibited an amorphous structure and their diameter was about 20-40 nm. There were no notable differences in morphology, surface area, and crystalline structure observed between them. Interestingly, the synthesis rate of nanocarbons from benzotrifluoride (20.3 mg/min) was almost three fold higher than that from benzene (7.6 mg/min). Moreover, a lower H/C ratio was observed in the case of nanocarbons from benzotrifluoride, indicating its more efficient H abstraction. The higher synthesis rate and lower H/C ratio of nanocarbons from benzotrifluoride were possibly attributed to the CF3 radicals generated in the reaction fields of solution plasma during synthesis.

DOI： 10.7567/JJAP.57.0102B6

Degradation of chitosan hydrogel dispersed in dilute carboxylic acids by solution plasma and evaluation of anticancer activity of degraded products

Chokradjaroen C., Rujiravanit R., Theeramunkong S., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Chitosan is a polysaccharide that has been extensively studied in the field of biomedicine, especially its water-soluble degraded products called chitooligosaccharides (COS). In this study, COS were produced by the degradation of chitosan hydrogel dispersed in a dilute solution (i.e., 1.55 mM) of various kinds of carboxylic acids using a non-thermal plasma technology called solution plasma (SP). The degradation rates of chitosan were influenced by the type of carboxylic acids, depending on the interaction between chitosan and each carboxylic acid. After SP treatment, the water-soluble degraded products containing COS could be easily separated from the water-insoluble residue of chitosan hydrogel by centrifugation. The production yields of the COS were mostly higher than 55%. Furthermore, the obtained COS products were evaluated for their inhibitory effect as well as their selectivity against human lung cancer cells (H460) and human lung normal cells (MRC-5).

DOI： 10.7567/JJAP.57.0102B5

In vitro cytotoxicity of carbon black nanoparticles synthesized from solution plasma on human lung fibroblast cells Open Access

Panomsuwan G., Chokradjaroen C., Rujiravanit R., Ueno T., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Carbon black nanoparticles (CB-NPs) have been synthesized from liquid benzene by a solution plasma method at room temperature and atmospheric pressure. The morphological observation by scanning electron microscopy revealed the agglomeration of aggregated fine particles. The synthesized CB-NPs were predominantly amorphous as confirmed by X-ray diffraction. The in vitro cytotoxicity of CB-NPs on the human lung fibroblast (MRC-5) cell line was assessed by the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and systematically compared with those of two types of commercial carbon blacks (i.e., Vulcan XC-72 and Ketjenblack EC-600JD). Cell viabilities were studied at different concentrations of 32.5, 65, 125, and 250 μg/mL. It was found that the CB-NPs derived from solution plasma exhibited a lower cytotoxicity on the MRC-5 cells than the other two comparative carbon blacks. The viability of MRC-5 cells exposed to CB-NPs remained higher than 90% even at a high concentration of 250 μg/mL. This result preliminarily confirmed the biosafety and potential use of CB-NPs in the field of biological applications.

DOI： 10.7567/JJAP.57.0102BG

Plasma in Solution and Its Applications Open Access

Saito N., Nakamura J., Shirafuji T., Ishizaki T.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Solution plasma: A new reaction field for nanomaterials synthesis Open Access

Saito N., Bratescu M.A., Hashimi K.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Solution plasma is a new electrical discharge process where an atmospheric non-equilibrium plasma is generated, usually at room temperature, in a liquid environment, such as an aqueous solution or an organic compound. There are a large variety of combinations used in experiments among solutions, electrode materials, plasma configurations, volumes, and reactor geometries, as well as the characteristics of the power supply. The solution plasma process (SPP) combines gas discharge physics, fluid thermodynamic properties, and fluid interfaces reactions. In SPP, nanoparticles with various sizes, shapes, crystallinities, and compositions could be obtained. The synthesis of carbon and hetero-carbon nanomaterials proves that SPP is an efficient and rapid method for their production. The polymerization of benzene in SPP can form graphene. By simply changing the organic precursor, carbon-doped nanostructures can be synthesized with a controlled composition. This review demonstrates that SPP is a new reaction field for nanomaterial production.

DOI： 10.7567/JJAP.57.0102A4

Solution plasma applications for the synthesis/modification of inorganic nanostructured materials and the treatment of natural polymers Open Access

Watthanaphanit A., Saito N.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Reducing the use of toxic chemicals, production steps, and time consumption are important concerns for researchers and process engineers to contribute in the quest for an efficient process in any production. If an equipment setup is simple, the process additionally becomes more profitable. Combination of the mentioned requirements has opened up various applications of the solution plasma process (SPP) - a physical means of generating plasma through an electrical discharge in a liquid medium at atmospheric pressure and room temperature. This review shows the progress of scientific research on the applications of the SPP for the synthesis/modification of inorganic nanostructured materials and the treatment of natural polymers. Development achieved in each application is demonstrated.

DOI： 10.7567/JJAP.57.0102A3

Synthesis of silicon-carbon black composite as anode material for lithium ion battery Open Access

Kim H., Yun Y., Lee Y.C., Lee M.H., Saito N., Kang J.

Japanese Journal of Applied Physics Vol. 57 ( 1 ) 2018.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics

Silicon has been attracting attention as an anode material that can be used for the design of high-capacity lithium ion batteries (LIB). However, the long-term cycling performance of silicon is limited owing to exfoliation from the current collector, resulting from volumetric expansion upon alloying with lithium in the charging process. However, carbon black is an agglomerate of primary particles that form a network and can incorporate a sufficient void space between network structures to accommodate the volumetric expansion of silicon. In this study, we propose the possibility of preventing the volume expansion and exfoliation of silicon by capturing silicon nanoparticles in the void space of the carbon black network. A silicon-carbon black composite material with this structure was successfully synthesized by solution plasma processing.

DOI： 10.7567/JJAP.57.0102B2

Enhancement of nitrogen self-doped nanocarbons electrocatalyst via tune-up solution plasma synthesis Open Access

Lee S., Saito N.

RSC Advances Vol. 8 ( 62 ) page： 35503 - 35511 2018

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

The development of a metal-free carbon based electrocatalyst for the oxygen reduction reaction (ORR) is an essential issue for energy conversion systems. Herein, we suggest a tune-up solution plasma (SP) synthesis based on a simple one-step and cost-effective method to fabricate nitrogen self-doped graphitic carbon nanosheets (NGS) as an electrocatalyst. This novel strategy using a low-pass filter circuit provides plasma stability and energy control during discharge in pyridine, determining the graphitic structure of nanocarbons doped with nitrogen. Notably, NGS have a relatively high surface area (621 m2 g−1), and high contents of nitrogen bonded as pyridinic-N and pyrrolic-N of 55.5 and 21.3%, respectively. As an efficient metal-free electrocatalyst, NGS exhibit a high onset potential (−0.18 V vs. Ag/AgCl) and a 3.8 transferred electron pathway for ORR in alkaline solution, as well as better long-term durability (4% current decrease after 10 000 s of operation) than commercial Pt/C (22% current drop). From this point of view, the nitrogen self-doped graphitic carbon nanosheet material synthesized using the tune-up SP system is a promising catalyst for the ORR, as an alternative to a Pt catalyst for application in energy conversion devices.

DOI： 10.1039/C8RA06614K

The solution plasma process for heteroatom-carbon nanosheets: The role of precursors Open Access

Hyun K., Saito N.

Scientific Reports Vol. 7 ( 1 ) 2017.12

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

The solution plasma process (SPP), known as non-equilibrium cold plasma at atmospheric pressure and room temperature, was used to investigate the synthesis of nitrogen-carbon nasnosheets (NCNs). To verify the effect of elementary composition and structure of N-methyl-2-pyrrolidone (NMP), various precursors were used in the SPP to synthesize NCNs via the bottom-up synthesis method for the first time. The NCNs were analyzed by transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Among the various precursors, SPP of 2-pyrrolidone was demonstrated to facilitate the formation of highly ordered NCNs. On the other hand, the SPP with cyclopentanone, cyclohexanone and pyrrole did not lead to the formation of carbon nanosheets. The results of this study would uncover new parameter fields for the growth of heteroatom-carbon nanosheets using this synthesis system. In addition, the study is expected to contribute toward research in improving the large-area growth and quality of two-dimensional nanostructures, such as heteroatom-carbon nanosheets or graphene, for various applications in other synthesis methods.

DOI： 10.1038/s41598-017-04190-x

Solution Plasma Process-Derived Defect-Induced Heterophase Anatase/Brookite TiO<inf>2</inf> Nanocrystals for Enhanced Gaseous Photocatalytic Performance Open Access

Pitchaimuthu S., Honda K., Suzuki S., Naito A., Suzuki N., Katsumata K.I., Nakata K., Ishida N., Kitamura N., Idemoto Y., Kondo T., Yuasa M., Takai O., Ueno T., Saito N., Fujishima A., Terashima C.

ACS Omega Vol. 3 ( 1 ) page： 898 - 905 2017.11

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

We report a simple room-temperature synthesis route for increasing the reactivity of a TiO2 photocatalyst using a solution plasma process (SPP). Hydrogen radicals generated from the SPP chamber interact with the TiO2 photocatalyst feedstock, transforming its crystalline phase and introducing oxygen vacancy defects. In this work, we examined a pure anatase TiO2 as a model feedstock because of its photocatalytic attributes and well-characterized properties. After the SPP treatment, the pure anatase crystalline phase was transformed to an anatase/brookite heterocrystalline phase with oxygen vacancies. Furthermore, the SPP treatment promoted the absorption of both UV and visible light by TiO2. As a result, TiO2 treated by the SPP for 3 h showed a high gaseous photocatalytic performance (91.1%) for acetaldehyde degradation to CO2 compared with the activity of untreated TiO2 (51%). The SPP-treated TiO2 was also more active than nitrogen-doped TiO2 driven by visible light (66%). The overall photocatalytic performance was related to the SPP treatment time. The SPP technique could be used to enhance the activity of readily available feedstocks with a short processing time. These results demonstrate the potential of this method for modifying narrow-band gap metal oxides, metal sulfides, and polymer composite-based catalyst materials. The modifications of these materials are not limited to photocatalysts and could be used in a wide range of energy and environment-based applications.

DOI： 10.1021/acsomega.7b01698

Synthesis of Few-Layer Graphene by Peeling Graphite Flakes via Electron Exchange in Solution Plasma

Chae S., Bratescu M., Saito N.

Journal of Physical Chemistry C Vol. 121 ( 42 ) page： 23793 - 23802 2017.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Physical Chemistry C

Compared with conventional graphene, few-layer graphene is an easy-to-use material because of its interesting mechanical and chemical properties. Meanwhile, solution plasma (SP) represents a nonequilibrium discharge, which induces electron exchange similar to a catalyst. Thus, SP serves as an electron donor and acceptor between organic molecules and graphite flakes in a solution. Finally, electron exchange leads to the formation of few-layer graphene by peeling graphite flakes. Furthermore, CN-functionalized few-layer graphene (f-FLG) exhibits excellent stability and dispersibility because of the balance of attractive and repulsive forces, i.e., the van der Waals force between the planes and the electrostatic force of the nitrile functional groups on the edges. In this study, f-FLG was successfully synthesized by peeling graphite flakes via electron exchange induced by SP in an aqueous solution containing an ionic liquid (IL) (1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA)). X-ray diffraction measurements revealed that the intensity of the 002 diffraction of graphite and the crystallite size along the [001] direction decreased to about 5 nm after SP treatment, indicating the progress of graphite flake peeling. Furthermore, the purified product comprised three layers with a crystallite size along the basal plane of about 80 nm evaluated by the deconvolution of the Raman 2D band. X-ray photoelectron spectroscopy confirmed that the synthesized f-FLG contains 7.7 atom % nitrogen, and the IR spectrum revealed the presence of the CN functional group. To understand the peeling mechanism, the ionization potential (IP) and electron affinity (EA) of the IL in water, and the averaged electron excitation temperature (Te) in plasma were estimated by ab initio molecular orbital calculations, cyclic voltammetry, and optical emission spectroscopy. An energy diagram of IP, EA, and Te shows that SP served to pump electrons for their circulation via EMIM-DCA and to remove electrons from graphite flakes and inject into f-FLG.

DOI： 10.1021/acs.jpcc.7b08516

Conversion of cellulose into reducing sugar by solution plasma process (SPP)

Prasertsung I., Chutinate P., Watthanaphanit A., Saito N., Damrongsakkul S.

Carbohydrate Polymers Vol. 172 page： 230 - 236 2017.9

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

In the present study, cellulose colloids are treated with the solution plasma process in order to prepare reducing sugar. The investigated parameters are treatment time, type of electrodes, and applied pulse frequency of the bipolar supply. The reducing sugar was characterized by DNS method and the%yield of total reducing sugar (TRS) was then calculated. The crystal structure and chemical structure of plasma-treated cellulose was measured by XRD and FT-IR, respectively. The%yield of TRS was greatly enhanced by solution plasma treatment using Fe electrode. SEM and TEM micrograph indicated that Fe electrode yield the incidental Fe nanoparticles, hypothesized to catalyze the cellulose degradation during SPP treatment. The crystal structure of cellulose was destroyed. Solution plasma treatment of cellulose using Fe electrode at the high applied frequency pulse provided the highest%TRS.

DOI： 10.1016/j.carbpol.2017.05.025

Generation of non-equilibrium condition in solution plasma discharge using low-pass filter circuit

Heo Y., Lee S., Bratescu M., Kim S., Lee G., Saito N.

Plasma Processes and Polymers Vol. 14 ( 8 ) 2017.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Plasma Processes and Polymers

Solution plasma process has been researched as one of the synthetic methods of nano- and functional materials using plasma discharge in liquids. In this study, a low-pass filter circuit was introduced to increase the density and temperature of electrons involved in a non-equilibrium condition. The discharge properties of the solution plasma generated by conventional and low-pass filter circuits were characterized and comparatively analyzed. Filtration of the MHz range current oscillations, an increase in the maximum discharge current, and a higher stability of solution plasma were obtained by simply inserting a resistor-capacitor (RC) component in the circuit, which leads to the increases in the density and temperature of electrons.

DOI： 10.1002/ppap.201600163

Simple Solution Plasma Synthesis of Hierarchical Nanoporous MnO<inf>2</inf> for Organic Dye Removal

Kim H., Watthanaphanit A., Saito N.

ACS Sustainable Chemistry and Engineering Vol. 5 ( 7 ) page： 5842 - 5851 2017.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Sustainable Chemistry and Engineering

We have demonstrated a simple and green approach to synthesize hierarchical nanoporous MnO2 by applying plasma in a liquid precursor; the approach is named the "solution plasma process (SPP)." Three types of sugar, i.e., glucose, fructose, and sucrose, were used as inducers for the nanoporous MnO2 formation (hereafter called G-MnO2, F-MnO2, and S-MnO2). These were successfully synthesized within a few minutes (7-19 min) under ambient conditions. It was confirmed that the generated numerous reactive species (e.g., electrons, radicals, and ions) accelerated the reduction of MnO4-. The reaction rate as well as the physical and chemical features of resulting products were found to be related to the type of sugars. Their high surface areas (F-MnO2 (169.1 m2·g-1) > G-MnO2 (141.0 m2·g-1) > S-MnO2 (85.5 m2·g-1)) provided efficient capability for the adsorption of cationic dye molecules, i.e., methylene blue. The dye removal efficiencies of all samples were >99% for an initial dye concentration (C0) of 10 mg·L-1 within 2 min and >82% for C0 = 50 mg·L-1 within 30 min. We expect that the synthesis route presented in this study can be extended to the large-scale production of effective adsorbents and to find practical applications for the industrial and green infrastructure.

DOI： 10.1021/acssuschemeng.7b00560

Enhanced degradation of chitosan by applying plasma treatment in combination with oxidizing agents for potential use as an anticancer agent

Chokradjaroen C., Rujiravanit R., Watthanaphanit A., Theeramunkong S., Saito N., Yamashita K., Arakawa R.

Carbohydrate Polymers Vol. 167 page： 1 - 11 2017.7

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

Solution plasma (SP) treatment in combination with oxidizing agents, i.e., hydrogen peroxide (H2O2), potassium persulfate (K2S2O8) and sodium nitrite (NaNO2) were adopted to chitosan degradation in order to achieve fast degradation rate, low chemicals used and high yield of low-molecular-weight chitosan and chitooligosaccharide (COS). Among the studied oxidizing agents, H2O2 was found to be the best choice in terms of appreciable molecular weight reduction without major change in chemical structure of the degraded products of chitosan. By the combination with SP treatment, dilute solution of H2O2 (4–60 mM) was required for effective degradation of chitosan. The combination of SP treatment and dilute solution of H2O2 (60 mM) resulted in the great reduction of molecular weight of chitosan and water-soluble chitosan was obtained as a major product. The resulting water-soluble chitosan was precipitated to obtain COS. An inhibitory effect against cervical cancer cell line (HeLa cells) of COS was also examined.

DOI： 10.1016/j.carbpol.2017.03.006

Crystallinity and surface state of cellulose in wet ball-milling process

Nemoto S., Ueno T., Watthanaphanit A., Hieda J., Saito N.

Journal of Applied Polymer Science Vol. 134 ( 22 ) 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Applied Polymer Science

We report the effect of wet ball-milling process under mild neutral salt conditions on the alteration of crystallinity and surface state of microcrystalline cellulose (MC). The ball-milling experiments were performed when the MC was immersed in H2O, NaCl aqueous solution, and KCl aqueous solution. Two collation groups, i.e., MC immersed in H2O2 and nonimmersed MC were additionally investigated for comparison. Except when H2O2 was present, the highest decrease in the cellulose crystallinity index (CI) was observed in dilute KCl. On the other hand, the CI of wet-milled MC/NaCl was greater than that of the wet-milled MC/H2O, however, still lower than that of the non-immersed MC. XPS results showed that the carbonization progressed in dry-milled MC and wet-milled MC/NaCl surfaces. Though, the surface oxidization progressed in wet-milled MC/H2O and wet-milled MC/KCl. Lastly, the ball-milling processes in different solutions led to various decreases of the crystallinity and the surface degradation due to carbonization and/or oxidization. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44903.

DOI： 10.1002/app.44903

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