研究者詳細 - 齋藤　永宏

論文 - 齋藤　永宏

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Accelerated Capacity and Cycling Performance via Facile Instantaneous Precipitation Induced Amorphization for Lithium-Ion Batteries 査読有り国際共著

Yang W., Huang J., Zhang Y., Saito N., Zhang Z., Yang L.

Small Methods 7 巻 ( 11 ) 2023年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Small Methods

Conversion-alloying anodes have garnered escalating attention with high theoretical capacity, however, they are seriously hindered by large volume distortion and capacity fading. To counter, structural modification needs more exploration. Herein, advantageous structure and high-performance are realized in new amorphous PbSb2O6 (PSO-a) nanosphere via facile instantaneous precipitation induced amorphization; conversion-alloying mechanism endows it with prominent lithium-storage capability; nanostructure can shorten ion-transfer distance and accommodate volume change outside the bulk of PSO-a; and loosely-stacked isotropic amorphous structure can enhance kinetics both at electrode/electrolyte interfaces and in the bulk. Volume change is synergistically stabilized from within to outside the bulk, leading to accelerated capacity and cycling. As expected, when employed in half-cells with 1 m LiPF6 in ethylene carbonate/diethyl carbonate/dimethyl carbonate/fluoroethylene carbonate (3:3:3:1 by mass) as electrolyte, glass microfiber filter as separator, and pure lithium foil as counter electrode, it realizes eminent performance with high specific capacity of 1512.6 mA h g−1 at 0.1 A g−1 and 755.1 mA h g−1 after 1000 cycles at 3 A g−1. To the best of the authors' knowledge, this is the first time PbSb2O6 is utilized as high-performance anode for lithium-ion batteries. Furthermore, this facile strategy provides a promising direction for high-performance amorphous anode material.

DOI： 10.1002/smtd.202300691

Correlation function of specific capacity and electrical conductivity on carbon materials by multivariate analysis 査読有り

Moon J., Yun H., Ukai J., Chokradjaroen C., Thiangtham S., Hashimoto T., Kim K., Sawada Y., Saito N.

Carbon 215 巻 2023年11月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Carbon

An attention to a Li ion battery for electric vehicles has been attracted, but there are two huge problems: a short mileage and slow charging speed. Therefore, it is required to improve the specific capacity and electrical conductivity of the carbon material used for an anode and a conductive agent. To solve these problems, this study organized correlation analysis with descriptor vectors by collecting experimental properties including capacity and conductivity from 21 various types of carbon materials. Focusing on the flux of Li ion, it was found that the capacity was dependent on the intercalation of Li ions, which lead to propose the correlation equation based on the Hill equation. Furthermore, the intercalation occurred at the edge of basal plane lead an increase of the width of the gap between two graphene layers, followed by a diffusion through the basal plane, finally the expanded gap recovered its original width. Also, it was found that the variables which are sensitive to the conductivity are largely dependent on the defects and especially the number of graphene layers around the surface, which proposed a correlation equation that can predict the capacity and conductivity. To validate these functions, we checked the effectiveness of it with both experimental data from 27 previous studies and statistical method. As a result, it was confirmed enough to predict them. Finally, a candidate structure for improving the battery performance was proposed, thus our study aims to guide the exploration of electrode materials for LIBs.

DOI： 10.1016/j.carbon.2023.118479

Search for stable host materials as low-voltage anodes for lithium-ion batteries: A mini-review 査読有り国際共著

Zhang Y., Huang J., Saito N., Zhang Z., Yang L., Hirano S.i.

Energy Storage Materials 55 巻頁： 364 - 387 2023年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Energy Storage Materials

The explosive demand for lithium-ion batteries (LIBs) in electric vehicles, portable electronics, and smart grids has spurred extensive research in recent years. The key to essential advances in LIBs depends on the search for stable host electrode materials with desirable energy and power densities. In the development of emerging stable host anode materials, the operating potential is an overlooked but crucial parameter because it deeply influences the energy, power, and safety of batteries. The ideal potential should not be too close to the lithium deposition potential like graphite (0.1 V vs. Li+/Li) which would trigger the formation of lithium dendrites under high rates, nor should be too high like spinel Li4Ti5O12 (> 1.5 V vs. Li+/Li) which compromises the batteries’ power and energy density. This mini-review firstly gives an account of several types of titanium-based and vanadium-based compounds as stable host anodes with the average operating potentials around or below 1 V vs. Li+/Li. The mechanisms for stable lithium storage and the origins of the low operating potentials are discussed by combining various characterization technologies. The key barriers and corresponding approaches are summarized for progressive electrochemical performance. Furthermore, several concise perspectives and challenges aiming at further theoretical prediction and practical application are provided.

DOI： 10.1016/j.ensm.2022.11.030

Nanoscale advanced carbons as an anode for lithium-ion battery 査読有り国際共著

Naraprawatphong R., Chokradjaroen C., Thiangtham S., Yang L., Saito N.

Materials Today Advances 16 巻 2022年12月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）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

Saccharide-originated fluorescent carbon dots synthesized by in-liquid plasma with controlled orderliness of carbon core through precursor alteration for selective and rapid metal ion detection 査読有り国際共著

Treepet S., Chokradjaroen C., Kim K., Saito N., Watthanaphanit A.

Materials Today Chemistry 26 巻 2022年12月

記述言語：英語掲載種別：研究論文（学術雑誌）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

Graphitic N-doped graphene via solution plasma with a single dielectric barrier 査読有り

Niu J., Chokradjaroen C., Saito N.

Carbon 199 巻頁： 347 - 356 2022年10月

記述言語：英語掲載種別：研究論文（学術雑誌）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

First-principles studies of enhanced oxygen reduction reactions on graphene- and nitrogen-doped graphene-coated platinum surfaces

Nam H.N., Phung Q.M., Choeichom P., Yamauchi Y., Saito N.

Physical Chemistry Chemical Physics 26 巻 ( 14 ) 頁： 10711 - 10722 2024年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physical Chemistry Chemical Physics

Developing innovative platinum-based electrocatalysts and enhancing their efficiency are crucial for advancing high-performance fuel cell technology. In this study, we employed DFT calculations to provide a theoretical basis for interpreting the impact of graphene coatings on various Pt surfaces on oxygen reduction reaction (ORR) catalytic activity, which are currently applied as protective layers in experiments. We comprehensively assess the geometric and electronic properties of Pt(100), Pt(110), and Pt(111) surfaces in comparison to their graphene-coated counterparts, revealing different adsorption behaviors of O2 across these surfaces. The ORR mechanisms on different Pt surfaces show distinct rate-determining steps, with Pt(111) showing the highest ORR activity, followed by Pt(110) and Pt(100). Graphene coatings play a key role in enhancing charge transfer from the surface, resulting in modifications of O2 adsorption. Despite influencing ORR kinetics, these graphene-coated surfaces demonstrate competitive catalytic activity compared to their bare counterparts. Notably, Pt(111) with a graphene coating exhibits the lowest activation energy among graphene-coated surfaces. Our calculations also suggest that the ORR can occur directly on non-defective Pt@graphene surfaces rather than being restricted to exposed Pt centers due to point defects on graphene. Furthermore, our work highlights the potential of nitrogen doping onto the Pt(111)@C surface to further enhance ORR activity. This finding positions nitrogen-doped Pt@C as a promising electrocatalyst for advancing electrochemical technologies.

DOI： 10.1039/d4cp00269e

Nanoarchitectonics Solution Plasma Polymerization of Amino-Rich Carbon Nanosorbents for Use in Enhanced Fluoride Removal 査読有り国際共著

Tipplook M., Tanaka H., Sudare T., Hagio T., Saito N., Teshima K.

ACS Applied Materials and Interfaces 16 巻 ( 6 ) 頁： 7038 - 7046 2024年2月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ACS Applied Materials and Interfaces

Amino-functionalized carbon (NH2C) is an effective adsorbent in removing pollutants from contaminated water because of its high specific surface area and electrical charge. In the conventional preparation method, the introduction of amino groups onto the carbon surface is limited, resulting in low pollutant adsorption. Herein, we present simultaneous carbonization and amination to form NH2C via electrical discharge of nonequilibrium plasma, and the resultant material is applied as an effective adsorbent in fluoride removal. The simultaneous process introduces numerous amino groups into the carbon framework, enhancing the adsorption efficiency. The fluoride adsorption capacity is approximately 121.12 mg g-1, which is several times higher than those reported in previous studies. Furthermore, computational modeling is performed to yield deeper mechanistic insights into the molecular-level adsorption behavior. These data are useful in designing and synthesizing advanced materials for applications in water remediation.

DOI： 10.1021/acsami.3c15172

Synthesis of crown-ether-embedded graphene by the solution plasma 査読有り国際共著

Kim H.m., Saito N., Kim D.w.

Carbon 216 巻 2024年1月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Carbon

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

DOI： 10.1016/j.carbon.2023.118578

A solid-solution approach for high frequency 3-dimensional isotropic negative-refractive-index metamaterials based on microwave ceramics 国際共著

Chang Q., Wang Z., Liu X., Saito N., Fan T.

Ceramics International 50 巻 ( 1 ) 頁： 772 - 780 2024年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Ceramics International

Negative refraction has yielded valuable insights and solutions in electromagnetics. However, progress in this field has been hindered primarily by implementation challenges, including the limited availability of raw materials and assembly difficulties, particularly at high frequencies. In this paper, a novel flexible self-assembly method was proposed, through which a controllable solid solution of close-packed structures can be attained. By integrating the flexible self-assembly method with an all-dielectric left-handed material structure, a negative-refractive-index metamaterial (NRIM) model was conceived. Magnetism is not a prerequisite under this scheme; therefore, a demonstration based on a microwave dielectric ceramic was proposed, wherein two subdivisions of close-packed structures were studied. Analysis of the field distribution and electromagnetic eigenmodes using finite element analysis revealed a negative refraction band at around 20 GHz, with a relative bandwidth of 4.2%. The analysis of dispersion behavior verified spatial isotropism in the NRIM. In summary, the designed passive NRIM only requires moderate dielectrics and is isotropic in three dimensions, thus bearing a high resemblance to natural mediums.

DOI： 10.1016/j.ceramint.2023.10.158

Regulated Phase Separation in Al–Ti–Cu–Co Alloys through Spark Plasma Sintering Process 査読有り

Lee S., Chokradjaroen C., Sawada Y., Yoon S., Saito N.

Materials 17 巻 ( 2 ) 2024年1月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials

With the goal of developing lightweight Al-Ti-containing multicomponent alloys with excellent mechanical strength, an Al–Ti–Cu–Co alloy with a phase-separated microstructure was prepared. The granulometry of metal particles was reduced using planetary ball milling. The particle size of the metal powders decreased as the ball milling time increased from 5, 7, to 15 h (i.e., 6.6 ± 6.4, 5.1 ± 4.3, and 3.2 ± 2.1 μm, respectively). The reduction in particle size and the dispersion of metal powders promoted enhanced diffusion during the spark plasma sintering process. This led to the micro-phase separation of the (Cu, Co)2AlTi (L21) phase, and the formation of a Cu-rich phase with embedded nanoscale Ti-rich (B2) precipitates. The Al–Ti–Cu–Co alloys prepared using powder metallurgy through the spark plasma sintering exhibited different hardnesses of 684, 710, and 791 HV, respectively, while maintaining a relatively low density of 5.8–5.9 g/cm3 (<6 g/cm3). The mechanical properties were improved due to a decrease in particle size achieved through increased ball milling time, leading to a finer grain size. The L21 phase, consisting of (Cu, Co)2AlTi, is the site of basic hardness performance, and the Cu-rich phase is the mechanical buffer layer between the L21 and B2 phases. The finer network structure of the Cu-rich phase also suppresses brittle fracture.

DOI： 10.3390/ma17020304

Conversion of fructose to 5-hydroxymethylfurfural using solution plasma process 査読有り国際共著

Klanarong N., Saito N., Prasertsung I., Damrongsakkul S.

Renewable Energy 218 巻 2023年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Renewable Energy

5-hydroxymethylfurfural (HMF), a key building block chemical derived from renewable lignocellulosic biomass, is used to produce a variety of derivatives for the biorefinery industry. In this work, the solution plasma process (SPP) was first applied to convert fructose, a key component from biomass, into HMF. Various conditions that affect fructose conversion and HMF yield were studied, including plasma treatment time (0–300 min), DMSO concentration (0–70%), electrode types (Iron; Fe and tungsten; W), system temperature (70–90 °C) and initial fructose concentration (10 g/L and 25 g/L). SPP was showed to enhance the conversion process to achieve high fructose conversion and HMF yield at the temperature (90 °C) lower than other conventional heating processes. The maximum fructose conversion and HMF yield were achieved at 95% and 76%, respectively at the DMSO concentration of 70% with Fe-electrodes, 90 °C of system temperature, 10 g/L of initial fructose concentration, 22.5 kHz of pulsed frequency and plasma treatment time of 240 min. Sulfuric acid formed from DMSO dissociation and Fe-nanoparticles from electrode erosion could effectively act as catalysts for the dehydration of fructose to HMF. SPP can be a high-potential tool for enhancing HMF production from the dehydration process in BCG economy.

DOI： 10.1016/j.renene.2023.119299

Highly durable graphene-encapsulated platinum-based electrocatalyst for oxygen reduction reactions synthesized by solution plasma process 査読有り

Park J.H., Kim K., Wang X., Huda M., Sawada Y., Matsuo Y., Saito N., Kawasumi M.

Journal of Power Sources 580 巻 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Power Sources

Though expensive platinum (Pt) is used as catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), insufficient durability remains as a bottleneck for commercialization of PEFCs. Improving both catalytic performance and durability by graphene encapsulation is an attractive strategy to solve this problem. In this study, graphene-encapsulated PtFe core-shell catalyst is synthesized with dimethyl formamide (DMF) and a pair of Pt and Fe electrodes without using any metal salts by utilizing the solution plasma (SP) process. TEM and EELS results show synthesized PtFe nanoparticles are encapsulated with close to single-layered highly crystallized graphene. Although commercial Pt/C showed significant performance degradation (ECSA −33%, MA −68%) after 50,000 cycles of accelerated durability test (ADT), PtFe core-shell catalyst shows remarkably improved durability (ECSA −13%, MA −19%) while graphene shell clearly remains. The improved durability is more prominent in the single cell test, the decrease in maximum power density after 6000 cycles of ADT was significantly lower as −1.2%, compared to that of Pt/C (−52.1%). This study introduces a novel and attractive catalyst synthesis process by the SP method followed by heat treatments and suggests graphene encapsulation can improve long-term durability of catalyst while maintaining ORR activity.

DOI： 10.1016/j.jpowsour.2023.233419

Novel solution plasma synthesis of highly durable carbon shell encapsulated platinum-based cathode catalyst for polymer electrolyte membrane fuel cells 査読有り

Park J.H., Saito N., Kawasumi M.

Carbon 214 巻 2023年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Carbon

Developing an effective method for synthesizing high-performance and durable catalysts for the oxygen reduction reaction is of great importance for cost reduction and the wide application of fuel cells. This study presents a simple and effective strategy using a plasma reaction in the liquid phase to synthesize carbon-shell-encapsulated Pt and PtFe catalysts. A carbon-shell-encapsulated PtFe catalyst alloyed with up to 29 at.% Fe exhibits a mass activity of 730 mA·mgpt−1 and a specific activity of 1772 μA cm−1, which are 2.4 and 5 times higher than that of commercial Pt/C, respectively. The carbon shell effectively maintained the low oxidation state of Pt by suppressing the formation of Pt–OH and significantly improved the durability of the catalyst in accelerated durability tests, increasing the gap in mass activity with Pt/C by a factor of up to six after 50,000 cycles. In addition, the decrease in the electrochemical surface area by the carbon shell enabled a more stable 4-electron reaction over a wide potential range. This study may provide fascinating insights into the effect of the carbon shell contributing to the improvement of the catalytic activity and durability of fuel cells as well as the novel plasma-based synthesis strategy of core-shell catalyst.

DOI： 10.1016/j.carbon.2023.118364

Preparation of lightweight, high hardness multi-component systems induced by partial oxidation and hard intermetallic phase formation 査読有り

Lee S., Chokradjaroen C., Sawada Y., Saito N.

Journal of Materials Research 38 巻 ( 18 ) 頁： 4235 - 4246 2023年9月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）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

Cationic nitrogen-doped graphene coated silver as low-work function electrode for inverted perovskite solar cells 査読有り

Yokoyama K., Lin H.S., Shui Q.J., Wang X., Saito N., Matsuo Y.

Applied Physics Express 16 巻 ( 8 ) 2023年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Applied Physics Express

Interfacial layers (ILs) located between the cathode and electron transport layer (ETL) in inverted perovskite solar cells are commonly required to achieve high-performance devices. Therefore, it is essential to develop excellent IL materials to improve efficiency and stability. This paper introduces the graphene-based IL material, namely cationic nitrogen-doped graphene (CNG), and evaluates its performance on a methylammonium lead iodide (MAPbI3)-type inverted perovskite solar cells. The device with a CNG IL achieved a power conversion efficiency of 13.5%, which is higher than a state-of-the-art reference using bathocuproine IL. Mechanistic studies demonstrated that the CNG IL can (1) efficiently collect electrons from the lowest unoccupied molecular orbital of ETL by lowering the work function of the silver cathode, (2) improve the conductivity of the silver electrode for better electron transfer, and (3) smooth out the interface contact between ETL and cathode to reduce defects in the device. As a result, the CNG IL enhanced the inverted perovskite solar cells performance by simultaneously increasing the open-circuit voltage, short-circuit current density, and fill factor. Moreover, the unencapsulated CNG IL-applied device demonstrated good long-term stability, with 96% efficiency retained over 1000 h in nitrogen atmosphere at room temperature.

DOI： 10.35848/1882-0786/acea18

Introducing micropores into carbon nanoparticles synthesized via a solution plasma process by thermal treatment and their charge storage properties in supercapacitors 査読有り国際共著

Thu M.M., Chaiammart N., Jongprateep O., Techapiesancharoenkij R., Thant A.A., Saito N., Panomsuwan G.

RSC Advances 13 巻 ( 24 ) 頁： 16136 - 16144 2023年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：RSC Advances

Carbon materials synthesized via a solution plasma process (SPP) have recently shown great potential for various applications. However, they mainly possess a meso-macroporous structure with a lack of micropores, which limits their applications for supercapacitors. Herein, carbon nanoparticles (CNPs) were synthesized from benzene via SPP and then subjected to thermal treatment at different temperatures (400, 600, 800, and 1000 °C) in an argon environment. The CNPs exhibited an amorphous phase and were more graphitized at high treatment temperatures. A small content of tungsten carbide particles was also observed, which were encapsulated in CNPs. An increase in treatment temperature led to an increase in the specific surface area of CNPs from 184 to 260 m2 g−1 through the development of micropores, while their meso-macropore structure remained unchanged. The oxygen content of CNPs decreased from 14.72 to 1.20 atom% as the treatment temperature increased due to the degradation of oxygen functionality. The charge storage properties of CNPs were evaluated for supercapacitor applications by electrochemical measurements using a three-electrode system in 1 M H2SO4 electrolyte. The CNPs treated at low temperatures exhibited an electric double layer and pseudocapacitive behavior due to the presence of quinone groups on the carbon surface. With increasing treatment temperature, the electric double layer behavior became more dominant, while pseudocapacitive behavior was suppressed due to the quinone degradation. Regarding cycling stability, the CNPs treated at high temperatures (with a lack of oxygen functionality) were more stable than those treated at low temperatures. This work highlights a way of introducing micropores into CNPs derived from SPP via thermal treatment, which could be helpful for controlling and adjusting their pore structure for supercapacitor applications.

DOI： 10.1039/d3ra02314a

Morphological Evolution of Gold Nanoparticles Synthesized via Solution Plasma Sputtering: Effect of Sodium Chloride Concentration and Storage Time 査読有り国際共著

Chantaramethakul J., Choophun N., Chokradjaroen C., Watthanaphanit A., Saito N., Panomsuwan G.

Journal of Physical Chemistry C 127 巻 ( 6 ) 頁： 3184 - 3193 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Physical Chemistry C

Morphological control of gold nanoparticles (AuNPs) is vital for tuning their optical, chemical, physical, and catalytic properties for desired specific applications. Despite numerous efforts dedicated in recent years, controlling the morphology of AuNPs synthesized via solution plasma sputtering (SPS) remains a challenge, requiring further investigation. Herein, AuNPs were synthesized via SPS in sodium chloride (NaCl) solutions of various concentrations (0.5, 1, 2, and 5 mM). Evolutions of localized surface plasmon resonance and morphology of AuNPs over a 30 day storage period were thoroughly examined using ultraviolet-visible spectroscopy and field-emission transmission electron microscopy. The formation and growth mechanisms of AuNPs during and after synthesis provide more insights into this nascent field. At the initial storage time, AuNPs with chain-like structures were observed at all the NaCl concentrations. Their size tended to increase from 6 to 10 nm with a broader size distribution with increasing NaCl concentration. At a prolonged storage time of 15 days, AuNPs became smaller and more isolated at all NaCl concentrations owing to the oxidative etching effect. After 30 days of storage, the number of Au ions dissolved from etching slowly reduced and grew on the AuNPs, affording increased particle sizes. The interplay between etching and growth processes proceeded until reaching equilibrium. AuNPs exhibited good colloidal stability at low NaCl concentrations (i.e., 0.5, 1, and 2 mM); however, coalescence and sedimentation occurred at a high NaCl concentration of 5 mM owing to a considerable reduction in the electrical double-layer thickness. These results demonstrated that the NaCl concentration and storage time crucially affect the morphological evolution and stability of AuNPs synthesized via SPS.

DOI： 10.1021/acs.jpcc.2c06474

A facile and efficient approach for the removal of high concentrations of ammonia nitrogen in wastewater: Liquid-phase plasma treatment 査読有り国際共著

Back S., Saito N., Lee S.

Journal of Environmental Chemical Engineering 11 巻 ( 1 ) 2023年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Journal of Environmental Chemical Engineering

We report the facile and effective liquid-phase plasma treatment (LPPT) approach for removing high concentrations of ammonia nitrogen from wastewater. The effects of the operating parameters, including the pH and temperature, the pulse repetition frequency, the pulse duration, and the reaction time, were investigated to obtain the optimal removal conditions using a simulated wastewater sample. It was found that a higher pulse repetition, a longer pulse duration, and alkaline conditions were favorable for the removal of ammonia nitrogen. Thus, at pH 12, a pulse repetition frequency of 30 kHz, and a pulse duration of 3.0 ?s, the removal efficiency of ammonia nitrogen reached 100% in 25 min during the LPPT. In addition, when isopropanol (IPA) and 1, 4-diazabicyclooctane triethylenediamine (DABCO) were used as scavengers for OH and 1O2, respectively, the removal efficiency of ammonia nitrogen after 25 min decreased from 71.7% to 68.1% in the presence of DABCO and from 71.7% to 62.8% in the presence of IPA. Based on these results, the mechanism of ammonia nitrogen removal was proposed to constitute the collision of accelerated electrons and the oxidation reaction of OH. Moreover, it was confirmed that the LPPT approach was feasible for the removal of ammonia nitrogen from wastewater.

DOI： 10.1016/j.jece.2022.109075

Carbon Fibers Prepared via Solution Plasma-Generated Seeds 査読有り

Romero Valenzuela A.E., Chokradjaroen C., Choeichom P., Wang X., Kim K., Saito N.

Materials 16 巻 ( 3 ) 2023年2月

担当区分：最終著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials

Carbon fibers are materials with potential applications for CO2 capture due to their porous structure and high surface areas. Nevertheless, controlling their porosity at a microscale remains challenging. The solution plasma (SP) process provides a fast synthesis route for carbon materials when organic precursors are used. During the discharge and formation of carbon materials in solution, a soot product-denominated solution plasma-generated seeds (SPGS) is simultaneously produced at room temperature and atmospheric pressure. Here, we propose a preparation method for carbon fibers with different and distinctive morphologies. The control over the morphology is also demonstrated by the use of different formulations.

DOI： 10.3390/ma16030906

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