出版者・発行元：Journal of Materials Research  

The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems were prepared by mechanical alloying in oxygen-lean atmosphere followed by spark plasma sintering. The ternary Mg–Al–Ti and quaternary Mg–Al–Ti–Cu systems which were sintered at 750 °C after 16 h milling showed the highest hardness of 509 and 947 HV with low densities of 2.9 and 3.9 g/cm3, respectively. The decrease in particle size and uniform dispersion of elements through optimization of the MA process induced the formation of uniform composite microstructure after SPS. Moreover, the addition of the fourth element, Cu, showed a significant impact on the improvement in hardness. This result was explained from the perspective of the microstructure and the electronic nature of elements. Our results provide a facile method for synthesizing oxide/metal composites from elemental powders without a separate oxidation process. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1557/s43578-023-01137-z

Scopus

出版者・発行元：Materials Today Advances  

Nanoscale advanced carbons, including carbon nanotube, graphene, carbon nanosphere, porous carbon, and their derivatives, are represented as distinct types of material generate in various forms, structure dimensions, and properties. They feature a large specific surface area, excellent conductivity, high mechanical properties, tunable chemical functionality, and a broad potential window, which essentially require for lithium-ion battery systems. The nanoscale advanced carbons have been intensively researched and developed as a negative electrode component to improve battery performance. This review deliberately discusses structures, main properties, and synthesis methods that are directly related to the physical properties and chemical behaviors of the nanoscale advanced carbons. Moreover, currently good candidates for anode material for lithium-ion batteries were summarized. The importance of the primary function and the synergistic effect of nanoscale advanced carbons with active electrode species is emphasized. The systematic information from this review provides a promising tool that represents an essential reference for selecting anode electrode materials and designing the next generation of advanced lithium-ion batteries.

DOI： 10.1016/j.mtadv.2022.100290

Scopus

出版者・発行元：Materials Today Chemistry  

Carbon dots (CDs) have grown interested in replacing metal-based quantum dots due to their fluorescent properties with low toxicity. The green synthesis, therefore, represents a contribution to this research field. Here, we demonstrate the synthesis of CDs from simple saccharides, including fructose, glucose, and sucrose, using an eco-friendly method—solution plasma (SP)—by applying plasma in the aqueous solution of the precursor. Variations and characterizations are conducted to understand the role or influence of each synthesis parameter, i.e. saccharide precursor's molecular structure, solution pH (2, 5, and 8), and post-treatment method (freeze-drying and heat-drying), in the materials' structure and fluorescent properties. Blue light-emitting CDs are prepared from all precursors of pH 5 and 8 through SP, followed by heat-drying. Results show that SP is responsible for the carbon core formation, and thus the precursor type affects the carbon core's orderliness. Heat-drying causes oxidation on the CDs' surface, whereby OH functional groups change to C=O. Among all samples, the CDs synthesized from fructose at pH 5 (Fru-CDs-5) perform the best photoluminescence property, having the highest quantum yield (QY) of 9.16% and exhibiting an outstanding ability to detect Fe3+ ions. This is the first attempt to evince the potential use of SP to synthesize CDs from natural carbon sources and obtain CDs exhibiting superior fluorescence properties without any doping and complex synthesis steps. In addition to offering a new synthetic approach, this work specifies the role of the SP and the effect of the saccharide's molecular structure, which is the most relevant synthesis parameters mandatory to obtain tailored CDs with precise control.

DOI： 10.1016/j.mtchem.2022.101139

Scopus

出版者・発行元：Coatings  

Global warming caused by CO2 emissions is a major environmental problem. Thus, the development of materials with innovative architectures that approach the CO2 problem is a necessity. In this study, hierarchical porous carbon fibers (HCFs) were synthesized by a chemical deposition process that operates at 400 °C and uses solution-plasma-generated soot (PGS) as a carbon precursor. Subsequently, the CO2 adsorption capacity of the synthesized material was evaluated. The HCFs showed enhanced surface areas and networks of micropores and mesopores. Moreover, the HCFs were post treated by metal etching and KOH activation. The post treated HCFs achieved a CO2 uptake of 0.8 mmol g−1 at 273 K, which was superior to the simultaneously produced solution plasma carbon (SPC), which has a CO2 uptake of 0.2 mmol g−1.

DOI： 10.3390/coatings12111620

Scopus

出版者・発行元：Coatings  

The solution plasma process (SPP) can provide a low-temperature reaction field, leading to an effective synthesis of N-doped graphene with a high N content and well-structured planar structure. However, the interactions at the plasma–solution interface have not been well understood; therefore, it needs to be urgently explored to achieve the modulation of the SPP. Here, to address the knowledge gap, we experimentally determined the physical parameters of the spital distribution in the plasma phase, plasma–gas phase, and gas–liquid phase of the SPP by the Langmuir probe system with modification. Based on the assumption that plasma can act similarly to semiconductors with the Fermi level above the vacuum level, an energy band diagram of the plasma–solution junction could be proposed for the first time. It was observed that the Fermi level of the organic molecule could determine the magnitude of electron temperature in plasma, i.e., benzene produced the highest electron temperature, followed by phenol, toluene, and aniline. Finally, we found that the electron temperature at the interface could induce quenching, leading to the formation of multilayer large-size-domain carbon products. It provided significant evidence for achieving nonequilibrium plasma modulation of carbon nanomaterial synthesis.

DOI： 10.3390/coatings12111607

Scopus

出版者・発行元：Carbon  

Graphitic nitrogen-doped graphene (g-NG) with significantly high nitrogen content, i.e., 18.79 at.%, could be produced by the electrical discharge in liquid, so-called “solution plasma”, with a single dielectric barrier. The proposed system could reduce the excessive current, resulting in stabilizing the glow plasma and maintaining the overall temperature. It could promote the preservation of nitrogen atoms from evaporation during the synthesis process and the formation of a graphitic carbon framework. Moreover, the influence of the precursors, i.e., six-membered ring organic molecules with and without the substitution of nitrogen atoms and the nitrogen-based functional groups, was also investigated to provide the guideline for the synthesis of g-NG via this proposed method. The substitution of nitrogen atoms in the benzene ring could be used to synthesize g-NG with higher nitrogen dopants, compared to the benzene ring with only nitrogen-based functional groups.

DOI： 10.1016/j.carbon.2022.08.032

Scopus

出版者・発行元：Materials Today Advances  

Solution plasma is an atmospheric nonequilibrium plasma generated by electrical discharge in liquid phase at room temperature. The plasma configurations, solutions, electrode materials, as well as the characteristics of the power supply can be easily tuned. Due to these features of the solution plasma, various sizes, shapes, compositions of products can be controlled, leading to the effective utilization in several applications, such as a novel catalyst for energy conversion. To accomplish the use of solution plasma as a promising tool for the synthesis and modification of advanced materials, fundamentals and applied knowledge related to the solution plasma should be reviewed and discussed. Therefore, in this review, fundamentals of plasma in liquid are explained relating to the solution plasma, and detailed advanced applications of solution plasma are organized. It is expected to give powerful knowledge to guide the researchers in designing plasma conditions and synthesizing catalysts for different applications in the future.

DOI： 10.1016/j.mtadv.2022.100244

Scopus

記述言語：英語   出版者・発行元：International Journal of Molecular Sciences  

Sustainability and environmental concerns have persuaded researchers to explore renewable materials, such as nature-derived polysaccharides, and add value by changing chemical structures with the aim to possess specific properties, like biological properties. Meanwhile, finding methods and strategies that can lower hazardous chemicals, simplify production steps, reduce time consumption, and acquire high-purified products is an important task that requires attention. To break through these issues, electrical discharging in aqueous solutions at atmospheric pressure and room temperature, referred to as the “solution plasma process”, has been introduced as a novel process for modification of nature-derived polysaccharides like chitin and chitosan. This review reveals insight into the electrical discharge in aqueous solutions and scientific progress on their application in a modification of chitin and chitosan, including degradation and deacetylation. The influencing parameters in the plasma process are intensively explained in order to provide a guideline for the modification of not only chitin and chitosan but also other nature-derived polysaccharides, aiming to address economic aspects and environmental concerns.

DOI： 10.3390/ijms22094308

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PubMed

DOI： 10.1038/s41598-021-85392-2

PubMed

記述言語：日本語   出版者・発行元：Materials Advances  

N-Doped few-layer graphene encapsulated Pt-based bimetallic nanoparticles were successfully synthesized via the solution plasma (SP) method. This synthesis strategy can be achieved in one pot by using only pure dimethylformamide (DMF) as the reaction solution at room temperature and atmospheric pressure. The structural analyses exhibited a fine core-shell structured nanoparticle (2-4 nm), which had Pt and Pt-based bimetallic nanoparticles as a core and N-doped few-layer graphene (NFG), having 2-4 layers, as a shell. Pt-based bimetallic cores (i.e., PtAu, PtAg, and PtPd) were varied depending on the metal electrodes used in the SP process. The electrocatalytic activity toward the oxygen reduction reaction (ORR) of the obtained samples in an acidic solution was found to be acceptable, while possessing excellent durability, compared to those of the commercial carbon-supported Pt catalyst. The effective ORR activity was possibly attributed to the synergistic effect of the Pt-based bimetallic core and N-doped graphene shell which contained high amounts of pyridinic-N and quaternary-N. The results in a single fuel cell test expressed the superiority of our SP-derived sample in the fuel cell performances to commercial Pt/C. This study not only proposed potential alternative ORR catalysts with acceptable electrocatalytic activity and high durability but also provided guidelines for the facile synthesis of carbon-based core-shell nanostructured materials with low chemical use via the SP process. This journal is

DOI： 10.1039/d0ma00718h

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出版者・発行元：Nano Express  

Herein, we report the synthesis of nitrogen-doped carbon dots (NCDs) through solution plasma (SP) for the first time. The SP method occurs a rapid dissociation of molecules, such as organic compounds, caused by an electrical discharge between electrodes immersed in a solution. The dissociation can result in the creation of various radicals such as ·C2, ·CN, and ·H which enable the rapid synthesis of carbon dots (CDs). The unique reaction of radicals allowed the formation of CDs with high N concentration and functionalization of the surface in a short time. In this study, by using the SP method, a very fine NCDs with size of 6 nm were synthesized from a pyridine/water mixture in just 10 min. Bright blue fluorescence (410 nm) with a high quantum yield (61%) was observed due to the high N concentration and the surface passivation. From the potential application point of view, the synthesized NCDs showed an excellent detection property for 2,4,6-trinitrophenol (TNP) by fluorescence quenching effect. It was due to rich amino-functional groups which act as a reaction pathway to TNP. This phenomenon was caused by the synergetic effect of a photo-induced electron transfer with the assistance of proton transfer-assisted electron transfer.

DOI： 10.1088/2632-959X/abb9fa

Scopus

記述言語：英語   出版者・発行元：Carbohydrate Polymers  

Electrical discharge plasma in a liquid phase can generate reactive species, e.g. hydroxyl radical, leading to rapid reactions including degradation of biopolymers. In this study, the effect of plasma treatment time on physical properties and cytotoxicity against cancer cells of N,O-carboxymethyl chitosan-stabilized gold nanoparticles (CMC-AuNPs) was investigated. AuNPs were synthesized by chemical reduction of HAuCl4 in 2 % CMC solution to obtain CMC-AuNPs, before being subjected to the plasma treatment. Results showed that the plasma treatment not only led to the reduction of hydrodynamic diameters of CMC-AuNPs from 400 nm to less than 100 nm by the plasma-induced degradation of CMC but also provided the narrow size distribution of AuNPs having diameters in the range of 2–50 nm, that were existing in CMC-AuNPs. In addition, the plasma-treated CMC-AuNPs could significantly reduce the percentage of cell viability of breast cancer cells by approximately 80 % compared to the original CMC and CMC-AuNPs.

DOI： 10.1016/j.carbpol.2020.116162

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PubMed

記述言語：英語   出版者・発行元：Carbohydrate Polymers  

Electrical discharge plasma occurring in a liquid phase, so called solution plasma, can generate highly active species, e.g. free radicals, which can involve in various chemical reactions, leading to less chemical uses. In this study, solution plasma was applied to deacetylation of chitin aiming to reduce the use of alkali. It was found that solution plasma could induce deacetylation of chitin hydrogels that were dispersed in MeOH/water solutions containing low NaOH concentrations (1–12%). Due to the action of free radicals, some extent of chain session of the polymer occurred during the plasma treatment. The degree of deacetylation and molecular weight of the obtained chitosan were 78% and 220 kDa, respectively, after the plasma treatment for five cycles (1 h/cycle) by using 90% MeOH/water solution containing 12% NaOH. The obtained chitosan could completely dissolve in 2% acetic acid solution and had antibacterial activities against S. aureus and E. coli.

DOI： 10.1016/j.carbpol.2019.115377

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PubMed

記述言語：日本語   出版者・発行元：ACS Applied Nano Materials  

Wrapping of gold nanoparticles (AuNPs) with a biocompatible matrix, to gain AuNP colloids, is a general strategy to synthesize the AuNPs for biomedical purposes. This work reports the synthesis of AuNP colloids in the aqueous solution of several natural matrices using a liquid-phase plasma process. Two classes of natural substances used are sugars (including: glucose, fructose, and sucrose) and biopolymers (including: carboxymethyl cellulose, sodium alginate, and gelatin). All are negatively charged water-soluble substances that are claimed to be sources of energy for cells to grow and have a high potential to be compatible with them. The study has emerged since one question arises: "Do these matrices also promote the growth of cancer cells?" The synthesis is performed by generating plasma across a pair of electrodes immersed in an aqueous solution of a natural matrix containing a gold precursor (HAuCl4·3H2O). Two concentrations of the matrices (0.5 and 1.0% w/v) are used, and the plasma treatment times are varied (0, 10, and 30 min). The effect of the type and concentration of natural matrices as well as the plasma treatment time on the formation of AuNPs, along with their physical and chemical properties, including morphology, size, hydrodynamic diameter (dh), colloidal stability, and charge on the AuNP surface, is evaluated. We find that the charge of the AuNP surfaces could be altered by the plasma treatment. Eventually, cytotoxicity test results against normal (MRC-5) and cancer (H460 and HeLa) cell lines could not only answer our opening question but also suggest a rather complex response. Our findings indicate the great potential of the obtained AuNP colloids as a part of cancer therapy.

DOI： 10.1021/acsanm.9b02106

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記述言語：英語   出版者・発行元：Carbohydrate Polymers  

Chitosan oligosaccharides, which obtain from degradation of chitosan, possess some interesting molecular weight-dependent biological properties, especially anticancer activity. Therefore, the conversion of chitosan to chitosan oligosaccharides with specific molecular weight has been continuously investigated in order to find effective strategies that can achieve both economic feasibility and environmental concerns. In this study, a novel process was developed to heterogeneously degrade chitosan powder by highly active species generated by electrical discharge plasma in a dilute salt solution (0.02 M) without the addition of other chemicals. The degradation rate obtained from the proposed process was comparable to that obtained from some other methods with the addition of acids and oxidizing agents. Separation of the water-soluble degraded products containing chitosan oligosaccharides from the reaction solution was simply done by filtration. The obtained chitosan oligosaccharides were further evaluated for an influence of their molecular weights on cytotoxicity against cancer cells and the selectivity toward cancer and normal cells.

DOI： 10.1016/j.carbpol.2018.08.037

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PubMed

記述言語：日本語   出版者・発行元：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

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記述言語：日本語   出版者・発行元：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

Web of Science

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記述言語：英語   出版者・発行元：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

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PubMed

開催年月日： 2017年

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Bangkok, Thailand  

開催年月日： 2016年

記述言語：英語   会議種別：口頭発表（一般）  

開催年月日： 2016年

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Osaka  

開催年月日： 2016年

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Bangkok, Thailand  

開催年月日： 2015年

記述言語：英語   会議種別：ポスター発表  

開催地：Munster, Germany  

開催年月日： 2015年

記述言語：英語   会議種別：口頭発表（一般）  

開催地：Bangkok, Thailand  

開催年月日： 2014年

開催地：Chiangmai, Thailand