Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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A phonon thermodynamics approach of gold nanofluids synthesized in solution plasma

Kang Heo Y., Antoaneta Bratescu M., Aburaya D., Saito N.

Applied Physics Letters Vol. 104 ( 11 ) 2014.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

The phonon thermodynamics theory for liquids was applied to explain the thermal characteristics of gold nanofluids synthesized by a simple, one-step, and chemical-free method using an electrical discharge in a liquid environment termed solution plasma process. The specific heat capacity of nanofluids was measured with a differential scanning calorimeter using the ratio between the differential heat flow rate and the heating rate. The decrease of the specific heat capacity with 10% of gold nanofluids relative to water was explained by the decrease of Frenkel relaxation time with 22%, considering a solid-like state model of liquids. © 2014 AIP Publishing LLC.

DOI： 10.1063/1.4868872

Depolymerization of chitosan-metal complexes via a solution plasma technique

Pornsunthorntawee O., Katepetch C., Vanichvattanadecha C., Saito N., Rujiravanit R.

Carbohydrate Polymers Vol. 102 ( 1 ) page： 504 - 512 2014.2

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

Chitosan-metal complexes were depolymerized under acidic conditions using a solution plasma system. Four different types of metal ions, including Ag +, Zn2+, Cu2+, and Fe3+ ions, were added to the chitosan solution at a metal-to-chitosan molar ratio of 1:8. The depolymerization rate was affected by the types of metal ions that form complexes with chitosan. The complexation of chitosan with Cu2+ or Fe3+ ions strongly promoted the depolymerization rate of chitosan using a solution plasma treatment. However, chitosan-Ag+ and chitosan-Zn2+ complexes exhibited no change in the depolymerization rate compared to chitosan. After plasma treatment of the chitosan-metal complexes, the depolymerized chitosan products were separated into water-insoluble and water-soluble fractions. The water-soluble fraction containing low-molecular-weight chitosan was obtained in a yield of less than 57% for the depolymerization of chitosan-Fe3+ complex with the plasma treatment time of 180 min. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbpol.2013.11.025

A novel one-step synthesis of gold nanoparticles in an alginate gel matrix by solution plasma sputtering

Watthanaphanit A., Panomsuwan G., Saito N.

RSC Advances Vol. 4 ( 4 ) page： 1622 - 1629 2014

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

We report a novel strategy to produce stable colloidal gold nanoparticles (AuNPs) in alginate aqueous solution which can be done in one step and without any chemicals. The AuNPs were produced by applying a voltage across a pair of gold electrodes which were immersed in alginate aqueous solution. Since the generation of AuNPs was caused by the sputtering of gold electrodes, the process was named the solution plasma sputtering (SPS) process. We utilize the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in a liquid environment, (2) to endow biocompatibility to the AuNPs, and (3) to provide colloidal stability to the AuNPs-alginate aqueous suspensions. The alginate concentrations were varied as 0.2, 0.5, and 0.9 %w/v. The concentration-dependent effect on the particle size of AuNPs, the physical absorption property and the stability of the AuNPs-alginate suspensions were studied. Results indicate that preparation of chemical-free colloidal AuNPs-alginate aqueous suspension is successful by the SPS process. The obtained colloidal suspensions were stable and able to retain their strong plasmon absorption bands within a reasonable time period. As a consequence, this is a high-potential technique to produce AuNPs suspended in alginate aqueous solution appropriate for biomedical applications. © 2014 The Royal Society of Chemistry.

DOI： 10.1039/c3ra45029e

Solution plasma exfoliation of graphene flakes from graphite electrodes

Lee H., Bratescu M., Ueno T., Saito N.

RSC Advances Vol. 4 ( 93 ) page： 51758 - 51765 2014

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

Graphene flakes were successfully produced by a simple method named a solution plasma process. The plasma was generated between two carbon electrode tips which were immersed in distilled water. The production approach is a continuous energy accumulation induced by focusing of plasma streamers on the surface of electrodes. This focused energy produces thermal gradient zones where a proper energy level is produced. Concisely, the energy is enough to extract graphene layers from the graphite structure but not enough to break covalent C-C bonds within the graphene sheets. Optical emission spectroscopy results showed the decomposition of carbon from the graphite electrodes with different intensities for the carbon species. Transmission electron microscopy images confirmed the hexagonal honeycomb structure of the graphene flakes. Furthermore, broadening of the 2D band in the Raman spectra revealed that the graphene flakes were disordered multilayers. This journal is

DOI： 10.1039/c4ra03253e

Solution plasma synthesis process of tungsten carbide on N-doped carbon nanocomposite with enhanced catalytic ORR activity and durability

Kim D., Li O., Pootawang P., Saito N.

RSC Advances Vol. 4 ( 32 ) page： 16813 - 16819 2014

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

In this study, the enhancement of ORR activity and durability by an N-doped carbon nanocomposite on tungsten carbide (WC) nanoparticles was reported. The nanocomposite of tungsten carbide on two different carbon matrices, pure carbon matrix (WC/C) and N-doped carbon matrix (WC/N-C), was at first prepared by a simple discharge process in the mixture of benzene/dodecane and pyrrole/dodecane. The nanoparticles of tungsten carbide were formed via the sputtering effect of tungsten electrodes during discharge. The results of TEM and XRD demonstrated that tungsten carbide nanoparticles with a mean size of 6 nm were evenly dispersed on both carbon matrices. The results of cyclic voltammetry measurements showed that both obtained metal/carbon matrices promoted a significant oxygen reduction reaction (ORR) in alkaline solution. The ORR potential of tungsten carbide/carbon matrix and nitrogen-doped carbon were -0.29 V and -0.36 V, respectively. The enhancement of ORR activity in WC/N-C was attributed to the combined catalytic effects of WC and N in the carbon matrix. Although the ORR activity of WC/N-C was still incomparable with commercial Pt/C, the durability of the catalyst was significant higher than that of Pt/C in a methanol environment. The catalyst did not exhibit an evident change of initial current after 4000 s. Therefore, the inexpensive N-doped WC/C nanocomposite might be a promising and highly durable catalytic material for cathodes in fuel cell applications. © 2014 the Partner Organisations.

DOI： 10.1039/c4ra02380c

Solution plasma synthesis of nitrogen-doped carbon nanoballs as effective metal-free electrocatalysts for oxygen reduction reaction

Panomsuwan G., Chiba S., Saito N., Ishizaki T.

Materials Research Society Symposium Proceedings Vol. 1641 2014

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Research Society Symposium Proceedings

Nitrogen-doped carbons nanoballs were synthesized from an organic liquid precursor (a mixture of benzene and pyrazine) by solution plasma process. After synthesis, they were further annealed at 700 and 900 °C under N2 atmosphere. The nitrogen-doped carbon nanoballs before and after thermal annealing process exhibit a similar morphological feature, and their diameters are in the range between 20 and 40 nm. With higher annealing temperature, the graphitization of the nitrogen-doped carbon nanoballs increases. For the electrocatalytic activity in an alkaline solution, the limiting current density and onset potential for the ORR activity can be significantly improved for the samples after thermal annealing at 900 °C. We anticipate that solution plasma process will be a viable alternative way for synthesizing heteroatom-doped carbon electrocatalysts for broad application in the field of fuel cells, metal-air batteries, and supercapacitors. © 2014 Materials Research Society.

DOI： 10.1557/opl.2014.319

Charge doping of large-area graphene by gold-alloy nanoparticles

Bratescu M., Saito N.

Journal of Physical Chemistry C Vol. 117 ( 50 ) page： 26804 - 26810 2013.12

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

We present a facile, one-step, and surfactant-free method for direct synthesis and loading of stable gold and gold-alloy nanoparticles (NPs) on large-area graphene using an electrical discharge in a liquid environment, termed solution plasma. We observed a charge doping of graphene by the gold NPs, which depends on the particles' chemical composition, even if the NPs contain a few percent of trivalent sp metals, such as indium (In) or gallium (Ga). Raman and electron energy loss spectroscopy (EELS) methods show that graphene is doped with electrons (n-type) in the case of gold NPs and with holes (p-type) in the case of gold-alloy NPs. The Raman band shift indicates that the amount of the transferred electrons from the gold NPs to graphene is -2 × 10 -4 electrons per unit cell. The gold-alloy NPs receive from graphene (2 and 4) × 10-5 electrons per unit cell if the gold NPs contain In and Ga, respectively. In the EELS spectra, the decrease in the intensity of the 1s-π* transition and the shift of the π* peak to higher energy confirm the depopulation of the antibonding states caused by the electron transfer from graphene to the gold-alloy NPs. © 2013 American Chemical Society.

DOI： 10.1021/jp409368c

Functionalization of multiwalled carbon nanotubes by solution plasma processing in ammonia aqueous solution and preparation of composite material with polyamide 6

Shirafuji T., Noguchi Y., Yamamoto T., Hieda J., Saito N., Takai O., Tsuchimoto A., Nojima K., Okabe Y.

Japanese Journal of Applied Physics Vol. 52 ( 12 ) 2013.12

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

Solution plasma processing (SPP) has been performed on multiwalled carbon nanotubes (MWCNTs) in ammonia aqueous solution. The MWCNTs, which do not disperse in aqueous solution, uniformly dispersed after the SPP. Only 2 h was required to obtain 10 g of the dispersed MWCNTs, while 7 days and additional chemicals were required for 185mg in a previous study. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy of the SPP-treated MWCNTs revealed that nitrogen- and oxygen-containing groups are formed on the MWCNTs. Serious damage to the MWCNT structure was not observed in the Raman spectrum or transmission electron microscopy images of the SPP-treated MWCNTs. The composite materials prepared using polyamide 6 with the SPP-treated MWCNTs showed better tensile, bending, and impact strength than those prepared with nontreated MWCNTs. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.125101

Gold nanoparticle synthesis using three-dimensionally integrated micro-solution plasmas

Shirafuji T., Ueda J., Nakamura A., Cho S.P., Saito N., Takai O.

Japanese Journal of Applied Physics Vol. 52 ( 12 ) 2013.12

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

Three-dimensionally integrated micro-solution plasmas (3D IMSPs), in which microplasmas are generated in gas bubbles in an aqueous solution held in a porous dielectric material, have been applied to gold nanoparticle synthesis. Conventional solution plasma processes require additional chemicals to increase the electrical conductivity of the aqueous solution for generating plasmas. In contrast to this, 3D IMSPs have been found to generate plasmas without such a procedure when the aqueous solution has a low electrical conductivity as in the case of HAuCl4 for gold nanoparticle synthesis. The gold nanoparticle synthesis has been confirmed through the observation of optical absorption due to the plasmon resonance at 550 nm, and also through the characterization of their size, crystallinity, and composition by transmission electron microscopy and energy dispersive X-ray spectroscopy. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.126202

Degradation of β-chitosan by solution plasma process (SPP)

Prasertsung I., Damrongsakkul S., Saito N.

Polymer Degradation and Stability Vol. 98 ( 10 ) page： 2089 - 2093 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

In this work, the solution plasma process (SPP) is used to treat β-chitosan solutions in order to induce the degradation of chitosan. The effects of solution plasma on the properties of chitosan solutions are investigated. The treatment time was varied from 0 to 300 min. The plasma-treated chitosan was characterized by the following methods; molecular weight by GPC, viscosity, crystal structure by XRD, chemical characteristics by FT-IR, solubility by UV-vis spectrophotometer, and fractional analysis. The results showed that after treatment with plasma for 15-120 min, the viscosity of the chitosan solution and apparent molecular weight of chitosans decreased remarkably, when compared to those of untreated sample. Longer treatment times had less effect on both viscosity and molecular weight of the samples. This suggested that the degradation process of chitosan occurred during plasma treatment. The XRD analysis showed that the crystallinity of chitosan was destroyed, resulting in amorphous structure. FT-IR analysis revealed that chemical structure of chitosan was not affected by solution plasma treatment. The %yield of water-soluble chitosan was increased with increasing plasma treatment time. These results implied that solution plasma process is able to induce the degradation of chitosan solutions. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.07.001

Highly efficient treatment of industrial wastewater by solution plasma with low environmental load

Cai L., Wu Y., Wu Y., Yamauti S., Saito N.

Water Science and Technology Vol. 68 ( 4 ) page： 923 - 928 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Water Science and Technology

Advanced oxidation techniques are efficient processes to dispose of organic contaminants in industrial wastewater with low secondary pollution. The solution plasma technique was featured as an advanced oxidation technique with low secondary pollution and high efficiency. However, the solution plasma technique reported previously could only treat wastewater of less than 200 mL owing to the limited plasma generated by only one pair of electrodes. In this work, multiple pairs of electrodes were installed at the bottom of the reaction vessel to generate plasma for decomposing methylene blue trihydrate (MB) and methyl orange (MO) solutions with a batch amount of 18 L/batch. The solution plasma technique was compared with direct ozonation in decomposition of MB and MO wastewater. A surprising phenomenon is that MO was more readily decomposed than MB by using direct ozonation, whereas the removal of MO was too low, and MB was more readily decomposed than MO by using the solution plasma technique. © IWA Publishing 2013.

DOI： 10.2166/wst.2013.321

Epitaxial growth of (111)-oriented BaTiO<inf>3</inf>/SrTiO<inf>3</inf> perovskite superlattices on Pt(111)/Ti/Al<inf>2</inf>O<inf>3</inf>(0001) substrates

Panomsuwan G., Takai O., Saito N.

Applied Physics Letters Vol. 103 ( 11 ) 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Applied Physics Letters

Symmetric BaTiO3/SrTiO3 (BTO/STO) superlattices (SLs) were epitaxially grown on Pt(111)/Ti/Al2O3(0001) substrates with various modulation periods (Λ = 4.8 - 48 nm) using double ion beam sputter deposition. The BTO/STO SLs exhibit high (111) orientation with two in-plane orientation variants related by a 180° rotation along the [111]Pt axis. The BTO layer is under an in-plane compressive state, whereas the STO layer is under an in-plane tensile state due to the effect of lattice mismatch. A remarkable enhancement of dielectric constant is observed for the SL with relatively small modulation period, which is attributed to both the interlayer biaxial strain effect and the Maxwell-Wagner effect. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4820780

Generation of three-dimensionally integrated micro solution plasmas and its application to decomposition of organic contaminants in water

Shirafuji T., Himeno Y., Saito N., Takai O.

Journal of Photopolymer Science and Technology Vol. 26 ( 4 ) page： 507 - 511 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Photopolymer Science and Technology

Three-dimensionally integrated micro solution plasmas were generated in gas bubbles in porous dielectric materials filled with gas/liquid mixed medium. The methylene blue molecules in aqueous solution were decomposed by the treatment with the three-dimensionally integrated micro solution plasmas. Decomposition efficiency was 16 times higher than conventional solution plasma in the case of applied voltage of 5 kV. With decreasing applied voltage from 5 to 2 kV, the decomposition efficiency was improved up to 360% in comparison to that of 5 kV, while reduction in the decomposition rate was 40%. © 2013 SPST.

DOI： 10.2494/photopolymer.26.507

Solution plasma synthesis process of carbon nano particles in organic solutions

Li H., Kang J., Urashima K., Saito N.

International Journal of Plasma Environmental Science and Technology Vol. 7 ( 1 ) page： 31 - 36 2013.9

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Plasma Environmental Science and Technology

In this study, solution plasma process (SPP) was applied to synthesis carbon nanoparticles in organic solution. In the SPP process, carbon nanoparticles were formed by carbon atoms supplied by two different groups of organic solutions, sugar and aromatic hydrocarbon solutions. Glucose, sucrose and fructose were used as sugar solution, whereas benzene and toluene were applied for the aromatic hydrocarbon solutions. Within the same group of solution, the carbon structure and size distribution were found to be similar. On average, 100 ml sugar solution produced 15 mg of carbon by weight. The particles included hemisphere and sphere in shape, with a size distribution between 100 - 600 nm. For aromatic hydrocarbon solutions, 930 and 1000 mg of carbon could be generated, respectively, from 100 ml of pure toluene and benzene. The particles were spherical shape with a size distribution of 20 - 30 nm. Fundamental characteristics of plasma discharge including voltage and current waveforms, as well as active species generated were compared. The discharge in sugar solution occurred in three different phases: pre-discharge, the initiation and the formation of discharge, whereas the discharge in benzene happened in two main steps: pre-discharging and the formation of discharge. From the optical emission spectrum, the major active species obtained from sugar solution were Hα (656 nm), followed by atomic O (777 nm), Hβ (486 nm) and relatively low intensity of atomic C (247 nm). For benzene and toluene solutions, the majority active species were observed to be C2 (513 nm) and CH (431 nm) and followed by Hα (656 nm). The results indicated pure benzene might be suitable solution applied for the synthesis of carbon nanoparticles in solution plasma process.

Crosslinking of a gelatin solutions induced by pulsed electrical discharges in solutions

Prasertsung I., Damrongsakkul S., Saito N.

Plasma Processes and Polymers Vol. 10 ( 9 ) page： 792 - 797 2013.9

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

This study uses discharges in solutions for the treatment of gelatin solutions in order to generate crosslinking. The effects of plasma on the properties of gelatin solutions were investigated, the latter including viscosity, amino acid contents, chemical analyses, and gel strengths. The results show that, after short duration plasma treatments (5-10 min), the viscosity of the gelatin solutions increased, while the concentration of OH · free radicals decreased. After adding ethanol to the gelatin solutions, a greater increase in viscosity, and a greater decrease in free radicals were found. This suggests that ethanol provides more free radicals that can promote the crosslinking of the gelatin solution during the plasma treatment, resulting in higher viscosity. The gel strength of the gelatin was greatly enhanced by the plasma treatment of the solution. The results regarding the free amino acid contents showed that the crosslinking degree of plasma-treated gelatin was higher than that of the untreated gelatin. FTIR measurements show that after plasma treatment, the IR bands at 1 668 and 1 558 cm-1, corresponding to the amide I and II groups of gelatin, shifted to higher wavenumbers, i.e. 1 672 and 1 564 cm-1, respectively. This suggests that crosslinking has occurred between gelatin molecules. The results show that discharges in solutions may be able to induce crosslinking reactions in the gelatin. Electrical discharges in solutions can be chemical-free, alternative crosslinking methods. Electrical discharges are investigated for the treatment of gelatin solutions as potential crosslinking, non-toxic methods. Plasmas were found to induce crosslinking of gelatin molecules, as demonstrated by the increased viscosity, decreased free amino contents, and increased gel strength. The addition of ethanol in gelatin solutions enhanced the crosslinking; this is because ethanol provides more free radicals necessary for crosslinking reactions. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/ppap.201200148

Synthesis of structure-controlled carbon nano spheres by solution plasma process

Kang J., Li O., Saito N.

Carbon Vol. 60 page： 292 - 298 2013.8

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

Structure-controlled carbon nanospheres (CNSs) were synthesized by an innovative plasma in liquid method, termed solution plasma processing (SPP). CNSs were formed by using benzene as a carbon precursor. Typically, 500 mg of CNSs were obtained from 100 ml of benzene with 20 min of treatment. The average diameters of CNSs increased from 20 to 100 nm when the pulse frequency of the bipolar power supply adjusted from 25 to 65 kHz. The TEM images showed that CNSs synthesized at 25-50 kHz consisted of amorphous carbon, while CNSs generated at 65 kHz were composed of continuous short range graphite with turbostratic structure. X-ray diffraction (XRD) patterns and TEM images showed that CNSs synthesized at 25-50 kHz had a low graphitization degree, while CNSs synthesized at 65 kHz consisted of graphite sheets with regular and ordering structure in basal planes. The increase of D/G intensity ratio in Raman spectroscopy confirmed the transition from amorphous carbon to nanocrystalline-graphite (NCG) with increasing pulse frequency. The resistivity of CNSs also increased with increasing pulse frequency. CNSs synthesized at 65 kHz have shown similar degree of resistivity as other commercial carbon black materials. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.carbon.2013.04.040

A simple synthesis method for nano-metal catalyst supported on mesoporous carbon: The solution plasma process

Kang J., Li O., Saito N.

Nanoscale Vol. 5 ( 15 ) page： 6874 - 6882 2013.7

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

High-electrocatalytic-activity noble nanoparticles (NPs) supported on carbon nanoballs (CNBs) were synthesized using an innovative plasma-in-liquid method, which is known as solution plasma processing (SPP). This technique uses a one-step method for the synthesis of NPs on carbon materials. CNBs are formed using benzene as a carbon precursor while gold (Au) or platinum (Pt) nanoparticles are generated instantaneously via sputtering from metal electrodes. The synthesized NP/CNBs were annealed at 850 °C in order to increase the conductivity of the material. The results of structural characterizations reveal that the Au and Pt NPs are smaller than 10 nm and have a uniform size distribution, and these NPs are successfully loaded onto highly mesoporous CNBs that have an average pore diameter between 13 and 16 nm. In the results from cyclic voltammetry measurements, the Au/CNBs and Pt/CNBs show clear peaks corresponding to the oxidation and reduction features in the catalytic reactions. Apart from noble nanoparticles, SPP can also be used to synthesize various kinds of NPs including bimetallic NPs loaded on spherical carbon supports by changing the working electrodes. The proposed mechanism for the synthesis is discussed in detail. This method shows potential to be a candidate for the next-generation synthesis of NP/carbon in the future. © 2013 The Royal Society of Chemistry.

DOI： 10.1039/c3nr01229h

One-step synthesis of gold bimetallic nanoparticles with various metal-compositions

Bratescu M., Takai O., Saito N.

Journal of Alloys and Compounds Vol. 562 page： 74 - 83 2013.6

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

A rapid, one-step process for the synthesis of bimetallic nanoparticles by simultaneous metal reduction and gold erosion in an aqueous solution discharge was investigated. Gold bimetallic nanoparticles were obtained by alloying gold with various types of metals belonging to one of the following categories: divalent sp metals, trivalent sp metals, 3d or 4d metals. The composition of the various gold bimetallic nanoparticles obtained depends on electrochemical factors, charge transfer between gold and other metal, and initial concentration of metal in solution. Transmission electron microscopy and energy dispersive spectroscopy show that the gold bimetallic nanoparticles were of mixed pattern, with sizes of between 5 and 20 nm. A red-shift of the surface plasmon resonance band in the case of the bimetallic nanoparticles Au-Fe, Au-Ga, and Au-In, and a blue-shift of the plasmon band of the Au-Ag nanoparticles was observed. In addition, the interaction of gold bimetallic nanoparticles with unpaired electrons, provided by a stable free radical molecule, was highest for those NPs obtained by alloying gold with a 3d metal. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2013.02.033

Effect of polymer concentration on the depolymerization of sodium alginate by the solution plasma process

Watthanaphanit A., Saito N.

Polymer Degradation and Stability Vol. 98 ( 5 ) page： 1072 - 1080 2013.5

Language：English Publishing type：Research paper (scientific journal) Publisher：Polymer Degradation and Stability

Depolymerization of alginate was accessed, for the first time, by the plasma treatment in solution called solution plasma process (SPP). The process was done by applying an electrical discharge into a reactor containing sodium alginate aqueous solution. The key of the production is the generation of reactive species induced by the plasma in a liquid environment that can lead to the scission of polymer chains. Effect of polymer concentration on the SPP processing parameters and the depolymerization efficiency were studied. Three concentrations of sodium alginate solutions, i.e., 0.2, 0.5, and 0.9 %w/v, were prepared. The results showed that increasing concentration of the alginate solution decreased the applied voltage required for the generation of plasma. Optical emission spectra demonstrated that the generation of reactive species was the highest at the lowest alginate concentration (i.e. 0.2 %w/v). Therefore, molecular weight reduction of this concentration after the SPP was more remarkable than the others. The most significant species required for the depolymerization of alginate was the reactive hydrogen species. Molecular weight distributions (MWD) of the obtained low molecular weight alginates (LMALGs) for all concentrations were narrow. Furthermore, reduction trends of molecular weight and viscosity of alginate with varying operation times indicated that the depolymerization of alginate in aqueous solution by the SPP was affected by the combined contribution of two factors: (1) the amount of reactive species generated during the process and (2) the degree of chain entanglement of the polymers. © 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.polymdegradstab.2013.01.011

Solution plasma sputtering processes for the synthesis of PtAu/C catalysts for Li-Air batteries

Terashima C., Iwai Y., Cho S.P., Ueno T., Zettsu N., Saito N., Takai O.

International Journal of Electrochemical Science Vol. 8 ( 4 ) page： 5407 - 5420 2013.4

Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Electrochemical Science

Clean, nanosized PtAu/C catalysts were fabricated, using a simple one-step synthesis technique that involved sputtering discharge in liquid, and did not require the use of chemical species such as surfactants and/or reductants. This solution plasma sputtering was driven by a pulsed power supply, and was performed on the discharge between Pt and Au targets in a liquid dispersion of carbon black. Fine PtAu nanoparticles with an average diameter of 5.7 nm were uniformly deposited on the carbon support. The production and composition of the PtAu nanoparticles could be controlled via changes in the sputtering conditions. The Au-rich Pt19Au81/C (atomic %) catalysts provided higher specific capacity, even in carbonate-based electrolyte Li-air batteries, reducing the amount of Li2CO3 that was deposited on the bare carbon. © 2013 by ESG.

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