Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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In situ synthesis of copper nanoparticles encapsulated by nitrogen-doped graphene at room temperature via solution plasma Open Access

Phan P.Q., Chae S., Pornaroontham P., Muta Y., Kim K., Wang X., Saito N.

RSC Advances Vol. 10 ( 60 ) page： 36627 - 36635 2020.10

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

Metal-carbon core-shell nanostructures have gained research interest due to their better performances in not only stability but also other properties, such as catalytic, optical, and electrical properties. However, they are limited by complicated synthesis approaches. Therefore, the development of a simple method for the synthesis of metal-carbon core-shell nanostructures is of great significance. In this work, a novel Cu-core encapsulated by a N-doped few-layer graphene shell was successfully synthesized in a one-pot in-liquid plasma discharge, so-called solution plasma (SP), to our knowledge for the first time. The synthesis was conducted at room temperature and atmospheric pressure by using a pair of copper electrodes submerged in a DMF solution as the precursor. The core-shell structure of the obtained products was confirmed by HR-TEM, while further insight information was explained from the results of XRD, Raman, and XPS measurements. The obtained Cu-core encapsulated by the N-doped few-layer graphene shell demonstrated relatively high stability in acid media, compared to the commercial bare Cu particles. Moreover, the stability was found to depend on the thickness of the N-doped few-layer graphene shell which can be tuned by adjusting the SP operating conditions. This journal is

DOI： 10.1039/d0ra07162e

Solution plasma: new synthesis method of N-doped carbon dots as ultra-sensitive fluorescence detector for 2,4,6-trinitrophenol Reviewed International coauthorship Open Access

Kim K., Chokradjaroen C., Saito N.

Nano Express Vol. 1 ( 2 ) 2020.9

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

Effect of electrical discharge plasma on cytotoxicity against cancer cells of N,O-carboxymethyl chitosan-stabilized gold nanoparticles Open Access

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

Carbohydrate Polymers Vol. 237 2020.6

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

Fabrication of biocomposite membrane with microcrystalline cellulose (MCC) extracted from sugarcane bagasse by phase inversion method

Thiangtham S., Runt J., Saito N., Manuspiya H.

Cellulose Vol. 27 ( 3 ) page： 1367 - 1384 2020.2

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

Abstract: The design of biocomposite membranes based on microcrystalline cellulose (MCC) extracted from sugarcane bagasse added into matrices of poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) was fabricated by the phase inversion method. The pore formation of biocomposite membranes was prepared by the phase inversion method, and the obtained biocomposite membranes showed a tunable microstructure formed in the membranes that was investigated by field-emission scanning electron microscope. Due to the high porosity and hydrophilic properties of MCC, the biocomposite membranes demonstrated excellent electrolyte wettability, large electrolyte uptake (up to 138%), and smaller interfacial resistance leading to enhancement of the ionic conductivity. Furthermore, the effects of MCC on the thermal properties of biocomposite membranes were evaluated by differential scanning calorimetry and the thermal shrinkage test. The addition of 5 wt% MCC showed the outstanding thermal stability of the biocomposite membranes. After thermal treatment at 135 °C for 1 h, this biocomposite membrane exhibited shrinkage of only 32% from the original shape while the PLA/PBS membrane showed shrinkage of 81%, which verifies that the introduction of MCC improves the thermal stabilities of biocomposite membranes. Promisingly, the biocomposite membranes represent candidate alternatives for future battery applications. Graphic abstract: [Figure not available: see fulltext.].

DOI： 10.1007/s10570-019-02866-3

Liquid-Phase Plasma-Assisted in Situ Synthesis of Amino-Rich Nanocarbon for Transition Metal Ion Adsorption

Tipplook M., Pornaroontham P., Watthanaphanit A., Saito N.

ACS Applied Nano Materials Vol. 3 ( 1 ) page： 218 - 228 2020.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

Amino-modified nanocarbon (NH2-C) has been widely used as an adsorbent for transition metal ion adsorption due to its high specific surface area, high electrical charge, and the ability to form a coordinate linkage to a transition metal ion. In this work, NH2-C was successfully synthesized from a mixture of phenol and (3-aminopropyl)triethoxysilane (APTES) through solution plasma processing, which performs both carbonization and amination simultaneously. This synthesis method eliminates the need to functionalize carbon with amino groups, as is required in the conventional process. Our NH2-C shows a better dispersion and a higher number of amino groups on both the external surface and inner pores, which enhances the adsorption capacity. The maximum capacities for Cu2+, Zn2+, and Cd2+ adsorption were 144.9, 115.4, and 102.0 mg g-1, respectively. These values were higher than those of five typical NH2-Cs synthesized by a conventional process. Based on the adsorption mechanism derived from adsorption kinetic, isotherm, and thermodynamic studies, the transition metal ions were chemisorbed to the surface in a monolayer endothermically and spontaneously. Moreover, it was found that NH2-C was suitable for use in ten consecutive adsorption-desorption cycles without significant loss of adsorption capacity.

DOI： 10.1021/acsanm.9b01915

Simultaneous deacetylation and degradation of chitin hydrogel by electrical discharge plasma using low sodium hydroxide concentrations Open Access

Rujiravanit R., Kantakanun M., Chokradjaroen C., Vanichvattanadecha C., Saito N.

Carbohydrate Polymers Vol. 228 2020.1

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

Synthesis of Au Nanoparticles in Natural Matrices by Liquid-Phase Plasma: Effects on Cytotoxic Activity against Normal and Cancer Cell Lines Reviewed International coauthorship

Treesukkasem N., Chokradjaroen C., Theeramunkong S., Saito N., Watthanaphanit A.

ACS Applied Nano Materials Vol. 2 ( 12 ) page： 8051 - 8062 2019.12

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

Nitriding an oxygen-doped nanocarbonaceous sorbent synthesized via solution plasma process for improving CO<inf>2</inf> adsorption capacity Open Access

Pornaroontham P., Panomsuwan G., Chae S., Saito N., Thouchprasitchai N., Phongboonchoo Y., Pongstabodee S.

Nanomaterials Vol. 9 ( 12 ) 2019.12

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

The synthesis of carbon nanoparticles (Cn) and oxygen-doped nanocarbon (OCn) was successfully done through a one-step synthesis by the solution plasma process (SPP). The Cn and OCn were nitrogen-doped by nitridation under an ammonia atmosphere at 800◦C for 2 h to yield NCn and NOCn, respectively, for carbon dioxide (CO2) adsorption. The NOCn exhibited the highest specific surface area (~570 m2 g−1) and highest CO2 adsorption capacity (1.63 mmol g−1 at 25◦C) among the synthesized samples. The primary nitrogen species on the surface of NOCn were pyridinic-N and pyrrolic-N. The synergistic effect of microporosity and nitrogen functionality on the NOCn surface played an essential role in CO2 adsorption enhancement. From the thermodynamic viewpoint, the CO2 adsorption on NOCn was physisorption, exothermic, and spontaneous. The NOCn showed a more negative enthalpy of adsorption, indicating its stronger interaction for CO2 on the surface, and hence, the higher adsorption capacity. The CO2 adsorption on NOCn over the whole pressure range at 25–55◦C best fitted the Toth model, suggesting monolayer adsorption on the heterogeneous surface. In addition, NOCn expressed a higher selective CO2 adsorption than Cn and so was a good candidate for multicycle adsorption.

DOI： 10.3390/nano9121776

Quantitative spectrochemical analysis of solution plasma in aromatic molecules

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

Plasma Processes and Polymers Vol. 16 ( 7 ) 2019.7

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

A nonthermal plasma produced at atmospheric pressure in the gas resulted from the surrounding liquid is named solution plasma (SP). A quantitative and comparative spectrochemical analysis of the plasma gas and solution in benzene, pyridine, and aniline is performed. The number densities of dicarbon and cyano radicals and hydrogen molecule from the plasma gas are measured using a cheap, straightforward, and home-made optical set-up. By simply modifying the optical set-up, the molar concentration of newly formed chemical compounds is in situ obtained in the solution. The thermodynamic properties of aromatic molecules determine the electrical breakdown and the species number densities in the plasma gas. The production rate and atomic composition of carbon material are correlated with the radicals from plasma gas.

DOI： 10.1002/ppap.201900012

P-Type Doping of Graphene with Cationic Nitrogen

Chae S., Panomsuwan G., Bratescu M.A., Teshima K., Saito N.

ACS Applied Nano Materials Vol. 2 ( 3 ) page： 1350 - 1355 2019.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Applied Nano Materials

Tailoring electrical properties of graphene by nitrogen doping is currently of great significance in a broad area of advanced applications. Bonding configuration of nitrogen atoms in graphene plays a vital role in controlling its electrical, chemical, and optical properties. Here, we report for the first time a simple bottom-up synthesis of a novel cationic nitrogen-doped graphene (CNG) by a solution plasma (SP). A mixture of ionic liquid and organic solvent was used as starting precursor. CNG exhibited an orthorhombic structure possibly due to the presence cationic nitrogen in hexagonal graphene lattice. Nitrogen doping content was found to be as high as 13.4 atom %. Electrical characterization demonstrated that the CNG exhibited a p-type semiconducting behavior with superior electrical conductivity and carrier concentration. Such unique electrical characteristics of CNG are mainly attributed to the presence of cationic nitrogen with preserved planar structure.

DOI： 10.1021/acsanm.8b02237

Production of reducing sugar from cassava starch waste (CSW) using solution plasma process (SPP)

Prasertsung I., Aroonraj K., Kamwilaisak K., Saito N., Damrongsakkul S.

Carbohydrate Polymers Vol. 205 page： 472 - 479 2019.2

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

The cassava starch processing plays an important role in food industries. During starch processing stage, a large amount of cassava starch waste (CSW) which mainly contains lost starch product and solid residue such as cassava bagasse are produced. Starch and cassava bagasse can be hydrolyzed into fermentable sugar such as glucose. In the present study, the solution plasma process (SPP) is used to treat CSW to prepare reducing sugar. The investigated parameters are treatment time, solvent concentration, applied pulsed frequency, and CSW concentration. The %yield of total reducing sugar (TRS) and glucose were calculated by DNS method and glucose assay kit, respectively. The chemical structure, morphology, and crystal structure of plasma-treated CSW were investigated. The results showed that the %yield of TRS was greatly enhanced by SPP treatment compared to that of acid hydrolysis. The CSW powder completely broke down into pieces after SPP treatment was applied. The amorphous and crystalline regions of CSW were destroyed during SPP treatment. SPP treatment of CSW with light sulfuric acid concentration of 0.08 M, applied pulsed frequency of 30 kHz, and CSW concentration of 0.5%w/v provided 99.0% TRS and 47.9% glucose.

DOI： 10.1016/j.carbpol.2018.10.090

Enhanced degradation of methylene blue by a solution plasma process catalyzed by incidentally co-generated copper nanoparticles

Prasertsung I., Kaewcharoen S., Kunpinit K., Yaowarat W., Saito N., Phenrat T.

Water Science and Technology Vol. 79 ( 5 ) page： 967 - 974 2019

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

This study presents a catalytic organic pollution treatment using the solution plasma process (SPP) with incidentally co-generated copper (Cu) nanoparticles via Cu electrode erosion. Methylene blue (MB) was used as a model organic contaminant. The treatment time was from 0 to 60 minutes at the plasma frequencies of 15 and 30 kHz. The treatment efficacy using the Cu electrode was compared with that of the tungsten (W) electrode. The high erosion-resistant W electrode provided no W nanoparticles, while the low erosion-resistant Cu electrode yielded incidental nanoparticles (10-20 nm), hypothesized to catalyze the MB degradation during the SPP. The percentage of MB degradation and the hydrogen peroxide (H2O2) generation were determined by an ultraviolet-visible spectrophotometer. The results showed that, after the SPP by the Cu electrode for 60 minutes, the MB was degraded up to 96%. Using the Cu electrode at a high plasma frequency strongly accelerated the Cu nanoparticle generation and MB treatment, although the amount of H2O2 generated during the SPP using the Cu electrode was less than that of the W electrode. The Cu nanoparticles were hypothesized to enhance MB degradation via both homogeneous (release of dissolved Cu ions) and heterogeneous (on the surface of the particles) catalytic processes.

DOI： 10.2166/wst.2019.035

Maximization of sodium storage capacity of pure carbon material used in sodium-ion batteries Reviewed International coauthorship

Kang J., Kim D.Y., Chae S.A., Saito N., Choi S.Y., Kim K.H.

Journal of Materials Chemistry A Vol. 7 ( 27 ) page： 16149 - 16160 2019

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A

Generally, carbon anode materials used in sodium-ion batteries do not exhibit good electrochemical performance because of low coulombic efficiency (CE). This paper presents a strategy to overcome this limitation by causing a co-intercalation reaction in a newly designed material. Here, Na was doped inside carbons and desodiation was caused by cleaning the doped Na. Consequently, the CE consistently exceeded 100%. Furthermore, new spaces were created when the doped Na was released continuously from the carbons, thereby allowing more Na to be stored in these spaces. This consistently increased the reversible capacity during cycling. Even though the designed material was a nanomaterial with a large specific surface area, the CE in the first cycle was 85%. Because of the co-intercalation reaction, a solid-electrolyte interphase (SEI) layer might not be formed depending on the anode surface structure and continuous long-term stable cycling was possible even without an SEI layer. Thus, a useful material for sodium-ion batteries can be designed using only carbons and without next-generation materials.

DOI： 10.1039/c9ta01751h

Solution plasma-assisted green synthesis of MnO <inf>2</inf> adsorbent and removal of cationic pollutant Open Access

Kim H., Saito N., Kim D.

Journal of Chemistry Vol. 2019 2019

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

In this study, we proposed the solution plasma-(SP-) assisted green synthesis method using plants extracts, i.e., glucose, with the expectation of acting as a reducing agent and promotor for the formation of powder state of nanostructured MnO 2 . MnO 2 was simply and rapidly synthesized within 10 min by the SP-assisted method. The structural features and morphology of as-synthesized MnO 2 were characterized by XRD, Raman, FE-SEM, and TEM analyses. For potential application of as-synthesized MnO 2 , cationic dye, i.e., methylene blue (MB), removal performance was investigated by batch experiment at an initial concentration of C 0 = 100 mg L -1 . The obtained MnO 2 exhibited effective dye removal ability given high C 0 , and simultaneously applied plasma discharging further enhanced removal efficiency. These contributions therefore open a new window not only on a powerful and environmentally benign synthesis route for efficient adsorbents but also on supporting multiple removal mechanism.

DOI： 10.1155/2019/7494292

Cytotoxicity against cancer cells of chitosan oligosaccharides prepared from chitosan powder degraded by electrical discharge plasma Open Access

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

Carbohydrate Polymers Vol. 201 page： 20 - 30 2018.12

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

Mechanistic aspect based on the role of reactive oxidizing species (ROS) in macroscopic level on the glycerol photooxidation over defected and defected-free TiO<inf>2</inf>

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

Journal of Photochemistry and Photobiology A: Chemistry Vol. 367 page： 270 - 281 2018.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Photochemistry and Photobiology A: Chemistry

The activity of commercial (defected-free) TiO2 and black (defected) TiO2 photocatalysts was comparatively tested in the glycerol photooxidation reaction. The preliminary results demonstrated that similar compounds, including glyceraldehyde (GCD), dihydroxyacetone (DHA), glycolic acid (GCOA), formaldehyde (FMD) and glycolaldehyde (GCAD), were generated from the photocatalytic oxidation of glycerol via both photocatalysts, but they differed in their yields. The black TiO2 exhibited a higher photocatalytic activity to convert glycerol than the commercial TiO2, due to the presence of some defective structure and its low band gap energy, and also promoted the generation of GCAD as the main product. In contrast, the commercial TiO2 promoted the formation of GCD as the major product. The principle reactive oxidizing species (ROS) contributing for glycerol conversion via black TiO2 can be ranked in the order of O2•->O12>OHb•>h+/OHs•>h+. The dominate ROS related to the conversion of glycerol to GCD and DHA were O2•- and OHb•, respectively. The main ROS to alter GCD and DHA to GCAD/FMD was O2•-, while the h+ was the principle ROS to convert GCD to GCOA. Finally, the pathway of glycerol conversion and product distribution over black TiO2 via various ROS in the presence of oxygen as electron acceptor is proposed.

DOI： 10.1016/j.jphotochem.2018.08.030

One-pot synthesis of purple benzene-derived MnO<inf>2</inf>-carbon hybrids and synergistic enhancement for the removal of cationic dyes Reviewed Open Access

Kim H., Saito N.

Scientific Reports Vol. 8 ( 1 ) 2018.12

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

MnO2-carbon hybrid (MnO2-C-PBz) was simultaneously synthesized by a one-step solution plasma process (SPP) using a single precursor referred to as "purple benzene", which was derived from the K+(dicyclohexano-18-crown-6 ether) complex. To clarify the synergistic effects on the cationic dye removal, MnO2-free carbon and carbon-free MnO2 samples were concurrently investigated. The results of adsorption for cationic dyes (methylene blue (MB) and rhodamine B (Rh B)) and anionic dye (methyl orange (MO)) revealed remarkably high affinity for cationic dyes. In particular, MnO2-C-PBz exhibited the highest adsorption capacity for MB, i.e., ∼3 times greater than that of the others. In addition, MnO2-C-PBz exhibited a rapid, high decolorization ability at C0 = 10 mg L-1 (within a few seconds, ∼99%) and at C0 = 100 mg L-1 (within 30 min, ∼81%), and the theoretical maximum monolayer adsorption capacity was 357.14 mg g-1 as calculated from the Langmuir adsorption isotherm equation. Furthermore, compared with carbon-free MnO2, MnO2-C-PBz exhibited quite a good cyclic stability. We expect that our findings give rise to the understanding of the synergistic effects of MnO2-carbon hybrid, as well as role of each components for the cationic dye adsorption, and may open an innovative synthesis approach to inorganic-organic hybrid materials.

DOI： 10.1038/s41598-018-22203-1

Narrowing band gap energy of defective black TiO<inf>2</inf> fabricated by solution plasma process and its photocatalytic activity on glycerol transformation

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

Journal of Alloys and Compounds Vol. 757 page： 188 - 199 2018.8

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

Defective black titania (TiO2) was synthesized by the solution plasma technique at ambient temperature and pressure. The effects of the electrolyte solution medium type (KCl and HNO3) and concentration (0.3 and 3.0 mM) as well as the plasma discharge time (1–4 h) with a Ti electrode were investigated. The 3.0 mM HNO3 solution provided the highest energy per second discharging into the plasma, resulting in both a high synthesis rate of black TiO2 and a high degree of defective structures, as monitored in terms of the Ti3+/Ti4+ ratio, which can shorten the band gap energy (Eg) of the obtained black TiO2. A long plasma discharge time (4 h) induced the formation of large particles of black TiO2, which appeared as a highly defective structure. Overall, the black TiO2 prepared by discharged plasma for 4 h in 3.0 mM HNO3 solution (BTN-304) provided the highest photocatalytic activity for glycerol conversion (58.49% at 24 h) and 4.85, 3.32, 2.11, 2.15, 39.15 and 26.61% yield of glyceraldehyde, dihydroxyacetone, hydroxypyruvic acid, glycolic acid, glycolaldehyde and formaldehyde, respectively. Pathway of glycerol conversion and product distribution over black TiO2 was attempted to propose. Finally, the reusability of the best black TiO2 was explored.

DOI： 10.1016/j.jallcom.2018.05.046

Thickness-Dependent Strain Evolution of Epitaxial SrTiO<inf>3</inf> Thin Films Grown by Ion Beam Sputter Deposition

Panomsuwan G., Saito N.

Crystal Research and Technology Vol. 53 ( 8 ) 2018.8

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

Epitaxial SrTiO3 (STO) thin films are grown on vicinal (001)-oriented LaAlO3 (LAO) substrates with various thicknesses (3–108 nm) by an ion beam sputter deposition (IBSD). Thickness-dependent strain in the STO films is investigated comprehensively through the X-ray analysis. The STO films grow on the LAO substrates under a compressive strain along in-plane direction (a- and b-axes) and a tensile strain along the growth direction (c-axis). With increasing film thickness, the STO unit cells evolve from more to less tetragonal structure, indicating the occurrence of strain relaxation. Quantitative strain analysis is also carried out for all STO films in terms of biaxial and hydrostatic components. It is found that the major cause of strain in STO films is caused by biaxial component over hydrostatic component. The surface morphology of STO films exhibit a step-and-terrace structure with roughness close to the LAO substrate (approx. 0.1 nm), indicating a 2D growth mode. However, as the film thickness increases, the surface terrace become rougher, which is caused by the effect of strain relaxation.

DOI： 10.1002/crat.201700211

Enhancing Bifunctional Catalytic Activity of Oxygen Reduction and Evolution Reaction via One-Pot Formation of MnO<inf>2</inf>-Carbon Hybrid Nanocomposite

Kim H., Saito N., Kim D.

ChemistrySelect Vol. 3 ( 23 ) page： 6302 - 6308 2018.6

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

While manganese dioxide (MnO2) is a promising bifunctional electrocatalyst for oxygen reduction and evolution reaction (ORR/OER) in alkaline media, electrochemical performance of bulk MnO2 limited by their poor electrical conductivity. Herein, we fabricate a MnO2-carbon nanoparticle hybrid composite (MO-CNP) by applying the plasma discharge in the single precursor of purple benzene. This synthesis route facilitates a simultaneous formation of MnO2 and carbon, which induced a homogeneously mixed and firmly anchored hybrid composite. As a result, as-obtained MO-CNP-1 shows more than 12 times higher electrical conductivity than that of prepared conventionally. Thus, formation of MO-CNP could be accompanied by a synergy between MnO2 and CNP as electrocatalyst, and consequently, electrochemical properties were significantly improved. In comparison with CNP, the ORR potential of MO-CNP-1 was positively shifted from –0.28 to –0.23 V (vs. Ag/AgCl), and current density has increased more than 2 times. Although the ORR activity of MO-CNP-1 was still far a little short of the commercial Pt/C, the MO-CNP-1 indicated significant higher OER activity, which demonstrated excellent overall catalytic capability of MO-CNP-1 as bifunctional catalyst.

DOI： 10.1002/slct.201800851

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