Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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

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

Solution plasma: A new reaction field for nanomaterials synthesis

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

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

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

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

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

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

The plasma-assisted formation of Ag@Co<inf>3</inf>O<inf>4</inf> core-shell hybrid nanocrystals for oxygen reduction reaction

Kim S.M., Jo Y.G., Lee M.H., Saito N., Kim J.W., Lee S.Y.

Electrochimica Acta Vol. 233 page： 123 - 133 2017.4

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

In this study, Ag@Co3O4 core-shell hybrid nanocrystals are synthesized using a plasma discharge in water for oxygen reduction reaction in alkaline solutions. A detailed analysis via electron microscopy in combination with EDS elemental mapping conclusively verifies that the reactive oxygen species generated from the plasma-assisted decomposition of water molecules govern the phase structure of the nanocrystals. Under oxidizing conditions, the Co oxide, which is more stable than the Ag oxide, provides the driving force for the segregation and preferential oxidation of Co at the surface. This leads to the formation of the core-shell architecture. The electrochemical measurements for the oxygen reduction reaction reveal that the specific activities of the Ag@Co3O4 core-shell nanocrystals are ca. 5.2 and 2.6 times higher than those of the pure Ag and Ag-Co alloy nanocrystals. The enhanced catalytic performance is attributed to the combination of electronic and geometric effects, which facilitates the O[sbnd]O bond breaking and desorption for the oxygen reduction. The insights gain through this study may serve as a foundation to design better electrochemical oxygen reduction electrocatalysts.

DOI： 10.1016/j.electacta.2017.03.049

Enhanced ferromagnetism in graphite-like carbon layer-coated ZnO crystals

Tu N., Dung N.H., Lan N.T., Nguyen K.T., Dung N.D., Viet D.X., Tuan N.T., Bui H.V., Nam D.V., Huy P.T., Saito N.

Journal of Alloys and Compounds Vol. 695 page： 233 - 237 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

We report on the preparation of graphite-like carbon-coated ZnO nanoparticles by ball milling a powder mixture of ZnO and C. Magnetic measurements indicated that carbon coating can strongly enhance the room-temperature ferromagnetism of ZnO nanoparticles, depending on preparation conditions. This enhancement may stem from robust ferromagnetism at the ZnO/C interface. The origin of interfacial ferromagnetism is attributed to crystallographic defects at the surface of ZnO crystals which are stabilized by the carbon shell layer.

DOI： 10.1016/j.jallcom.2016.10.200

Facile preparation of defective black TiO<inf>2</inf> through the solution plasma process: Effect of parametric changes for plasma discharge on its structural and optical properties

Jedsukontorn T., Ueno T., Saito N., Hunsom M.

Journal of Alloys and Compounds Vol. 726 page： 567 - 577 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

Defective TiO2 or black TiO2 nanoparticles (NPs) are remarkably attractive for photocatalytic applications, since the defect-disordered structure crucially affects the optical properties. In this work, high visible light-active black TiO2 NPs were synthesized by an innovative solution plasma process (SPP) with a titanium (Ti) electrode in HNO3 solution. The effects of the plasma operating parameters, in terms of the pulse frequency (20–80 kHz) and pulse width (0.5–2.0 μs) under two different HNO3 concentrations (0.3 mM and 3.0 mM) on the morphology, structural and optical properties of the obtained black TiO2 NPs were explored. Increasing the pulse frequency, pulse width and concentration of HNO3 all increased the input energy per pulse and energy per second, which induced an increased volume-based particle size, synthesis rate and Ti3+/Ti4+ ratio, but decreased the rutile mass fraction, the Ti-OH/TiO ratio and the band gap energy of the obtained black TiO2 NPs. Among all the prepared black TiO2 NP samples, those prepared at a pulse frequency of 20 kHz, pulse width of 2 μs (energy input per second of 17.3 J) in 3.0 mM HNO3 exhibited the highest visible-light absorption capability (the lowest band gap energy of ∼2.44 eV). The variation in the band gap energy was more strongly dependent on the Ti3+/Ti4+ ratio than the Ti-OH/TiO ratio in the structure of black TiO2 NPs.

DOI： 10.1016/j.jallcom.2017.08.028

New insights into vegetable oil pyrolysis by cold plasma technique

Meeprasertsagool P., Watthanaphanit A., Ueno T., Saito N., Reubroycharoen P.

Energy Procedia Vol. 138 page： 1153 - 1158 2017

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

Green liquid fuels are alternatively produced by pyrolysis of vegetable oil. Still, this process requires high processing temperature and high energy consumption per unit cost. Recently, solution/liquid-phase plasma (cold plasma) is the novel method to provide the direct energy at highly excited energy state. In this study, the investigation of the green fuel synthesis from vegetables oils using cold plasma was examined. The cold plasma reactor was connected to a bipolar pulsed power supply under 200 ml of palm oil, the pulse frequency adjusted from 15-45 kHz and the voltage adjusted in ranges of 1.2-1.5 kV with 40 minutes of discharge times, pulse width 2 μs, electrode distance 0.5 mm. Properties of generated plasma were investigated by optical emission spectroscopy (OES) methods. The liquid products were analysed by GC-MS. In order to identify components of the liquid product, a GC-MS chromatogram was carried out; the main peaks were oleic acid and palmitic acid. Therefore, the other peak showed which products were cracked to short-chain hydrocarbon and hexadecane was one of the compounds which were cracked in palm oil. In conclusion, the results showed that plasma has potential and enough energy to convert vegetable oils in liquid fuels at room temperature which can also provide the direct energy better than pyrolysis.

DOI： 10.1016/j.egypro.2017.10.224

Photocatalytic behavior of metal-decorated TiO<inf>2</inf> and their catalytic activity for transformation of glycerol to value added compounds

Jedsukontorn T., Saito N., Hunsom M.

Molecular Catalysis Vol. 432 page： 160 - 171 2017

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

In this work, TiO2 was decorated with one of four different metals (Bi, Pd, Pt and Au) by sol immobilization at ambient condition. The individual addition of each metals on the TiO2 did not affect the crystallite size or band gap energy of TiO2, but increased its visible light absorption ability due to the localized surface plasmon resonance effect of the doped metals, except for Bi, as well as the mechanism of the charge transfer. Among all the prepared metal-decorated TiO2 photocatalysts, Au/TiO2 exhibited the highest visible light absorption ability and an appropriate mechanism of charge transfer, which consequently alleviated the e−–h+ recombination. It also provided the highest photocatalytic activity for glycerol conversion (92.8% at 14 h) and yield of dihydroxyacetone, glyceraldehyde, glycolic acid, hydroxypyruvic acid and formaldehyde of 12.0, 23.1, 10.7, 13.6 and 15.3%, respectively.

DOI： 10.1016/j.mcat.2017.02.022

Novel synthesis of PtPd nanoparticles with good electrocatalytic activity and durability

Zhang J., Hu X., Yang B., Su N., Huang H., Cheng J., Yang H., Saito N.

Journal of Alloys and Compounds Vol. 709 page： 588 - 595 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds

PtPd nanoparticles in the size range of 2–5 nm have been directly synthesized from their metal wire electrodes via a one-step plasma sputtering technique in a solution of water and methanol under atmospheric pressure. PtPd nanoparticles produced in the water/methanol solution have good dispersibility compared with those produced in water because methanol successfully reduces the aggregation of the nanoparticles during the plasma sputtering process. Further, the solution plasma technique provides a novel reaction field with a highly energetic state for the PtPd nanoparticle synthesis. KB-supported PtPd nanoparticles (PtPd/KB, 12 wt% Pt) exhibit excellent electrocatalytic activity (over 4 times mass activity compared with commercial Pt/C) and stability (maintaining 43% mass activity after 300 cycles) towards methanol electrooxidation because of their large electrochemical surface area (ECSA, that is 2.5 times greater than that of commercial Pt/C) and synergistic effect of the binary alloy. Thus, as-synthesized PtPd/KB catalysts may have potential applications in direct methanol fuel cells (DMFCs) to lower their cost and improve their cycle efficiency.

DOI： 10.1016/j.jallcom.2017.03.202

Simple introduction of carboxyl head group with alkyl spacer onto multiwalled carbon nanotubes by solution plasma process

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

Japanese Journal of Applied Physics Vol. 56 ( 9 ) 2017

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

A simple method of fabricating carboxyl-terminated multiwalled carbon nanotubes (MWCNTs) with alkyl spacers was developed to improve the dispersion quality of MWCNTs in aqueous solutions using solution plasma (SP) in a 6-aminocaproic acid solution. The formation of SP in the solution led to better dispersion of MWCNTs in aqueous solutions. Fourier transform infrared spectroscopy (FT-IR) results indicate that a carboxyl group with an alkyl spacer can be introduced by SP treatment in the 6-aminocaproic acid solution. Sedimentation tests show that the SP-treated MWCNTs in the 6-aminocaproic acid solution retained their good dispersion quality in aqueous solutions of pHs 5 6 and 9. The alkyl spacer plays an important role in the preservation of dispersion states particularly at pH 6.

DOI： 10.7567/JJAP.56.096202

Synthesis of carbon nanoparticles from used motor oil and benzene via solution plasma process

Seangarunthong N., Khongthong P., Panomsuwan G., Ueno T., Saito N., Eiad-Ua A.

Key Engineering Materials Vol. 751 KEM page： 773 - 778 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：Key Engineering Materials

Carbon nanoparticles (CNPs) were successfully synthesized from the mixture of used motor oil and benzene via a solution plasma process (SPP). The synthesis was achieved within a single step at room temperature and atmospheric pressure. The effects of mixing ratio between used motor oil and benzene on the physical and chemical properties of CNPs were investigated by means of field-emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy. The results revealed that there were no significant changes in morphological feature and chemical functional groups on CNPs at different mixing ratios. The CNPs exhibited the aggregates of fine particles with the diameter of about 20-30 nm. The crystallinity of CNPs was found to be slightly increased when synthesized under the presence of used motor oil, possibly due to the effect of aliphatic hydrocarbons and polycyclic aromatic hydrocarbons in used motor oil. We expect that the conversion of used motor oil into CNPs by SPP could be another attractive way to add the value to used motor oil prior to disposing.

DOI： 10.4028/www.scientific.net/KEM.751.773

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