研究者詳細 - 小川　智史

論文 - 小川　智史

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Analysis of phase transformation in Mg<inf>2</inf>NiH<inf>4</inf> via in situ synchrotron X-ray measurements

Towata S.i., Noritake T., Ogawa S., Nakanishi Y., Sakuma Y., Tachiki S., Hirotomo T., Suda K.

Journal of Alloys and Compounds 938 巻 2023年3月

出版者・発行元：Journal of Alloys and Compounds

Mg-based alloys such as Mg2NiH4 are still attracting attention as high-capacity hydrogen storage materials. Mg2NiH4 undergoes the phase transformation between low-temperature (LT) and high temperature (HT) phases near the hydrogen desorption temperature. Herein, the crystallographic changes of Mg2NiH4 were investigated to clarify the behavior of the phase transformation by in situ synchrotron radiation X-ray measurements. The samples with three thermal histories (slow cooling, quenching from the HT phase, and hydrogenation below the transformation temperature) were prepared. These thermal histories affected the ratio of the LT phase without microtwinning (LT1) and with microtwinning (LT2). As the LT2/LT1 ratio increases, the phase transformation temperature decreases, and the phase transformation accelerates. X-ray diffraction peak analyses showed that the crystallite size and the lattice strain depend on the thermal history of the sample. X-ray absorption spectra indicated an increase in the short-range disorder of Mg2NiH4 when hydrogenated below the transformation temperature, which causes anomalous phase transformation and modulates the transformation temperature.

DOI： 10.1016/j.jallcom.2022.168594

Sulfur in humin as a redox-active element for extracellular electron transfer

Pham D.M., Oji H., Yagi S., Ogawa S., Katayama A.

Geoderma 408 巻 2022年2月

記述言語：日本語出版者・発行元：Geoderma

Humin (HM), an insoluble humic substance that occurs as an organo-mineral complex, mediates extracellular electron transfer (EET) among microorganisms in the geosphere. Although sulfur (S)-containing functional groups have been posited as possible redox-active groups in HM, there has been no direct evidence in this regard. Here, we characterized the redox-active S in HM from different natural sources using synchrotron radiation-based X-ray absorption spectroscopy in partial fluorescence yield mode. The S content in HM is less than 0.9%, with the oxidation states ranged widely from −2 to +6. About 9% to 19% of total S in HM was redox variable, corresponding to 1.2 × 10−5 to 17.1 × 10−5 Eq/g-HM redox capacity. The redox capacity of HM driven by S is comparable to or larger than the electron donating capacity of HM observed in anaerobic microbial dechlorination of pentachlorophenol, suggesting that S is one of the significant redox-active elements in HM. These findings provide new insights into the role of S cycling in biogeochemical processes and microbial energy networks.

DOI： 10.1016/j.geoderma.2021.115580

Effects of the amount of Au nanoparticles on the visible light response of TiO<inf>2</inf> photocatalysts

Yoshida T., Misu Y., Yamamoto M., Tanabe T., Kumagai J., Ogawa S., Yagi S.

Catalysis Today 352 巻頁： 34 - 38 2020年8月

記述言語：日本語出版者・発行元：Catalysis Today

We have succeeded to prepare Au nanopareticle deposited TiO2 photocatalysts (Au/TiO2) with control of Au nanoparticle size to be around 8 nm and variation of number density using a colloid photodepostion method. The prepared Au/TiO2 exhibits activity on decomposition (oxidation) of formic acid by thermally activated and photo-activated catalytic reactions. The thermally activated catalytic decomposition gradually increases with increasing the number density of deposited Au NPs and saturated, suggesting that the decomposition occurs on Au NPs surface and/or near the interface of TiO2 and Au NPs. On the other hand, the photocatalytic decomposition is significantly improved with rather small number density deposition of Au NPs and disappeared with high number density deposition. ESR measurements of Au/TiO2 in the surrounding similar to the photocatalytic decomposition suggests that electrons excited by plasmon resonance absorption in the Au NPs transfer to TiO2 to promote the decomposition. However, high number density deposition enhances electron capture by neighboring Au NPs and reduces the photocatalytic activity. Thus there should be the optimum number density of Au NPs on TiO2 for photocatalytic decomposition of formic acid.

DOI： 10.1016/j.cattod.2019.12.035

Comparison of platinum photodeposition processes on two types of titanium dioxide photocatalysts

Yamamoto M., Minoura Y., Akatsuka M., Ogawa S., Yagi S., Yamamoto A., Yoshida H., Yoshida T.

Physical Chemistry Chemical Physics 22 巻 ( 16 ) 頁： 8730 - 8738 2020年4月

記述言語：日本語出版者・発行元：Physical Chemistry Chemical Physics

The photodeposition method is useful for the preparation of metal-loaded photocatalysts, by which the metal precursors are adsorbed on the photocatalyst surface and reduced by photoexcited electrons to typically form metallic nanoparticles. In the present study, the photodeposition process of Pt nanoparticles was investigated on anatase and rutile TiO2photocatalysts. It was found that on the anatase surface, only some of the Pt4+precursors were first adsorbed in an adsorption equilibrium and reduced to form a smaller number of initial metal species; then, they functioned as electron receivers to reduce the remaining precursors on their metallic surfaces and become larger particles. In contrast, the rutile surface can adsorb most of the precursors and quickly reduce them upon photoirradiation to form nanoparticles, giving a larger number of small nanoparticles. As a result, the Pt-loaded rutile photocatalyst exhibited higher activity in hydrogen evolution from an aqueous methanol solution than the Pt-loaded anatase photocatalyst.

DOI： 10.1039/c9cp06988g

Erratum: Characterization by synchrotron-radiation X-ray photoelectron spectroscopy of NO adsorption on Rh (e-Journal of Surface Science and Nanotechnology (2019) (17) (69−70) DOI: 10.1380/ejssnt.2018.36)

Koda Y., Sumida H., Ogawa S., Tsukada C., Namatame H.

e-Journal of Surface Science and Nanotechnology 17 巻頁： 69 - 70 2019年7月

記述言語：日本語出版者・発行元：e-Journal of Surface Science and Nanotechnology

Figures 3 and 4 in the original article [1] were inappropriately displayed. Correct figures are shown below. “Table 1” and “Table 3” that appear in the text on p. 39 in Ref. 1 should be replaced by “Table I” and “Table III”, respectively. The publisher found that they occurred during the production process. None of the corrections change any discussion and conclusions of the article. (Figure Presented).

DOI： 10.1380/ejssnt.2019.69

Development of sample preparation technique to characterize chemical structure of humin by synchrotron-radiation–based X-ray photoelectron spectroscopy

Pham D.M., Miyata Y., Awata T., Nakatake M., Zhang C.F., Kanda K., Ogawa S., Ohta S., Yagi S., Katayama A.

Surface and Interface Analysis 51 巻 ( 2 ) 頁： 226 - 233 2019年2月

記述言語：日本語出版者・発行元：Surface and Interface Analysis

Carbon-binding state of humin (HM, a non-conductive insoluble organo-mineral humic substance) was successfully characterized for the first time by synchrotron-radiation–based X-ray photoelectron spectroscopy (XPS). Four sample preparation techniques—HM on double-sided carbon tape, indium sheet, copper mesh, and in pellet formed from the mixture of HM and copper powder (Cu) at different mixing ratios (1:1, 1:2, and 1:6 v/v)—were compared. The results show that HM samples prepared using the first three methods had significant charge buildup, which made the interpretation of the XPS spectra impossible because of the shifts in the binding energy of C 1s XPS spectra. Pellets of HM:Cu mixture enhanced the electrical conductivity and reduced charge buildup on the sample surface. Pellets prepared with HM:Cu ratio of 1:1 (v/v) provided the minimum charge buildup and high sensitivity with difference in C 1s spectra regardless of the observing position. The C 1s spectra, estimated by the subtraction of the carbon contamination in Cu, showed the resolution of CC (284.0 eV), CC/CH (285.1 eV), CO (286.3 eV), CO (287.3 eV), and OCO (288.3 eV) and three additional peaks of CF (289.3 eV), CF2 (290.2 eV), and CF3 (291.4 eV). Soft X-ray absorption spectroscopic (XAS) analysis further proved the existence of fluoride (F 1s) in HM structure. The detection of fluorinated carbon in HM showed a great advancement of XPS compared with other conventional analyses. X-ray with the incident angle of 0° provided the smallest (nearly negligible) energy shift in the C 1s spectra of HM and did not damage the surface of the sample.

DOI： 10.1002/sia.6574

Surface chemical states of gold nanoparticles prepared using the solution-plasma method in a CsCl aqueous solution

Tsukada C., Yoshida H., Ogawa S., Yoshigoe A., Yagi S., Yaita T.

Surface and Interface Analysis 51 巻 ( 1 ) 頁： 85 - 88 2019年1月

記述言語：日本語出版者・発行元：Surface and Interface Analysis

In this study, gold nanoparticles (AuNPs) prepared in a 5 mM CsCl aqueous solution using the solution-plasma method are characterized via transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The particle diameter is measured over the process time via TEM. During the solution-plasma process, small particles of 2.1 to 2.2-nm diameter are generated in the CsCl aqueous solution; these particles then enlarge via Ostwald ripening over time until they reach an equilibrium size of ~13 nm after 36 days. In addition, the surface chemical states of the AuNPs are characterized at different depths via SR-XPS. The SR-XPS measurements obtained using incident X-ray energy (hν) of 945.0 eV revealed that Cs─Au, Cl─Au, and Cs─Cl─Au bonds are present 1.2 nm below the surface. The measurements obtained at an incident X-ray energy of 2515.0 eV showed that Cs─Cl─Au bonding is also present 2.5 nm below the surface, indicating that Cs and Cl strongly interact with Au. The TEM and SR-XPS measurements revealed that 2 processes occur cyclically during the growth process via Ostwald ripening: (i) the Cs and Cl in the aqueous solution adsorb on the AuNP surface and (ii) Au atoms subsequently bond to the AuNPs surface.

DOI： 10.1002/sia.6555

Au nanorods fabricated by means of solution plasma method

Tsukada, C; Mizutani, T; Ogawa, S; Nameki, H; Yagi, S

SURFACE AND INTERFACE ANALYSIS 48 巻 ( 11 ) 頁： 1248 - 1251 2016年11月

記述言語：日本語出版者・発行元：Surface and Interface Analysis

Au nanorods with a low toxicity are important in medical field. The nanorods are generally fabricated by using cetyltrimethylammonium bromide (CTAB), which has a high toxicity. We have attempted the fabrication of Au nanorods without CTAB reagent. In this study, Au nanoparticles as growth seeds of the nanorods have been fabricated by using Au rods and NaCl aqueous solution. Subsequently, Au3+ ions of HAuCl4 have been reduced in the mixing solution, which includes the Au nanoparticles and the NaCl aqueous solution, by means of the solution plasma between W rods. The amount of Au3+ ion has been directly monitored during the solution plasma process by using in-situ UV–Vis-NIR. The fabricated solution possesses the Au nanoparticles of shapes of rod, sphere, triangle plate and hexagonal plate, respectively. The Au nanorods may be fabricated by both aggregating the reduced Au3+ ion at the surfaces of the Au nanoparticles as the growth seeds and controlling the growth orientation of the Au nanorods by the adsorption of Cl− ions on Au{100} facets. To control the narrow dispersion relation between the short and the long axes lengths of the Au nanorods, the addition of HAuCl4 aqueous solution in small volume steps is a key point. Copyright © 2016 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.6096

Hydrogen storage of Pd/Mg composite nanoparticles fabricated by gas evaporation method

Ogawa S., Suzuki H., Tsukada C., Yoshida T., Yagi S.

e-Journal of Surface Science and Nanotechnology 14 巻頁： 150 - 153 2016年5月

出版者・発行元：e-Journal of Surface Science and Nanotechnology

Mg nanoparticles covered with the Pd nanoparticles (Pd/Mg NPs) have been fabricated by the gas evaporation method using He gas. The coaxial formation of the Mg and Pd NPs enables to fabricate the Pd/Mg NPs. The surfaces of the Pd and Mg NPs are quite clean because only pure He gas has been used during the fabrication of the NPs. The surface and interface chemical states of the Pd/Mg NPs have been investigated by X-ray photoelectron spectroscopy (XPS) without the exposure to the air. The XPS investigation has revealed that the formation of the interfacial alloy state between the Mg and Pd NPs. The Pd/Mg NPs can absorb the hydrogen at the room temperature by the hydrogenation of the most of the Mg atoms inside the Pd/Mg NPs.

DOI： 10.1380/ejssnt.2016.150

XAFS analysis for quantification of the gallium coordinations in Al2O3-supported Ga2O3 photocatalysts

Akatsuka M., Yoshida T., Yamamoto N., Yamamoto M., Ogawa S., Yagi S.

16TH INTERNATIONAL CONFERENCE ON X-RAY ABSORPTION FINE STRUCTURE (XAFS16) 712 巻 ( 1 ) 2016年

記述言語：日本語出版者・発行元：Journal of Physics: Conference Series

Ga2O3 loaded Al2O3 samples (Ga2O3/Al2O3) were prepared to change coordination structures around Ga atoms. Ga K-edge XANES spectra of the Ga2O3/Al2O3 samples showed two peaks assigned to Ga atoms having tetrahedral coordination structure (Ga(t)) and octahedral one (Ga(o)). Curve-fitting analysis of XANES spectra was carried out with a set of pseudo- Voight and arctangent functions, and the fractions of Ga(t) and Ga(o) were quantitatively estimated from the ratio of the peak areas. EXAFS curve-fitting analysis also evaluated the fractions of Ga(t) and Ga(o) and they were in good agreement with those obtained by XANES analysis. It was revealed that the fraction of Ga(t) increased with the decrease in the loading amount of Ga2O3 due to the interaction of Ga species with Al2O3. The fractions of Ga(t) and Ga(o) might relate to the photocatalytic activity for CO2 reduction with H2O over the Ga2O3/Al2O3 samples.

DOI： 10.1088/1742-6596/712/1/012056

Characterization of nitrogen ion implanted TiO<sub>2</sub> photocatalysts by XAFS and XPS

Yoshida, T; Niimi, S; Yamamoto, M; Ogawa, S; Nomoto, T; Yagi, S

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS 365 巻頁： 79 - 81 2015年12月

記述言語：日本語出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

A nitrogen doped TiO2 as a visible-light response photocatalyst was prepared by N+ implantation technique. N+-implanted TiO2 samples promoted the photocatalytic activity for degradation of methylene blue under visible-light irradiation. XANES and XPS analyses indicated two types of chemical state of nitrogen, one photo-catalytically active N substituting the O sites and the other inactive NOx (1 ≤ x ≤ 2) species. In the valence band XPS spectrum of the high activity sample, the additional electronic states were observed just above the valence band edge of a TiO2. The electronic state would be originated from the substitutional nitrogen and be responsible for the band gap narrowing, i.e., visible light response of TiO2 photocatalysts.

DOI： 10.1016/j.nimb.2015.04.010

In situ UV-vis investigation of growth of gold nanoparticles prepared by solution plasma sputtering in NaCl solution

Mizutani, T; Ogawa, S; Murai, T; Nameki, H; Yoshida, T; Yagi, S

APPLIED SURFACE SCIENCE 354 巻頁： 397 - 400 2015年11月

記述言語：日本語出版者・発行元：Applied Surface Science

Gold nanoparticles are prepared in various concentrations of NaCl solutions by solution plasma sputtering. The absorption spectra of these solutions during and after the plasma process are measured by in situ ultraviolet-visible (UV-vis) spectroscopy to estimate the particle diameters and concentrations of gold. The distributions of particle diameters are obtained by transmission electron microscope (TEM) observations. These experiments indicate the gold nanoparticles with about 2.2 nm are directly formed by plasma phase and the diameters are increasing over time. These increases of particle diameters are caused by Ostwald ripening of gold nanoparticles in NaCl solution. We estimate the equilibrium diameter at which the gold nanoparticles are not solved in NaCl solution using in situ UV-vis spectroscopy. These diameters are about 5, 7 and 10 nm in 3, 5 and 10 mM NaCl solution, respectively. We make it possible to control the diameter of gold nanoparticles prepared by solution plasma sputtering in NaCl solution.

DOI： 10.1016/j.apsusc.2015.04.139

Hydrogen storage property of materials composed of Mg nanoparticles and Ni nanoparticles fabricated by gas evaporation method

Fujimoto, T; Ogawa, S; Kanai, T; Uchiyama, N; Yoshida, T; Yagi, S

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 40 巻 ( 35 ) 頁： 11890 - 11894 2015年9月

出版者・発行元：International Journal of Hydrogen Energy

We have fabricated the materials composed of the Mg and the Ni nanoparticles and clarified the hydrogen storage property by using TEM, XPS and QCM. The Mg and the Ni nanoparticles have been fabricated by gas evaporation method and been mixed. The diameters of the Mg and the Ni nanoparticles have been estimated as 20.0 ± 8.4 and 4.7 ± 2.0 nm, respectively. And the Mg and the Ni nanoparticles as prepared sample possess almost clean surface. This sample can absorb the hydrogen under atmospheric pressure at 30 °C before completely oxidized. However, the hydrogen storage ability of this sample has been lost by the adsorption of residual gases even under vacuum condition in several hours after the end of fabrication. Due to the Mg oxide shell on the surface of the Mg nanoparticles is formed by the residual gases, the hydrogenation of the Mg nanoparticles are hindered.

DOI： 10.1016/j.ijhydene.2015.05.031

Hydrogen storage of binary nanoparticles composed of Mg and Pd

Ogawa, S; Fujimoto, T; Mizutani, T; Ogawa, M; Uchiyama, N; Kato, K; Ohta, T; Yoshida, T; Yagi, S

INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 40 巻 ( 35 ) 頁： 11895 - 11901 2015年9月

Hydrogen storage property of the Pd nanoparticle with clean surfaces studied by QCM

Ogawa S., Fujimoto T., Kanai T., Uchiyama N., Tsukada C., Yoshida T., Yagi S.

e-Journal of Surface Science and Nanotechnology 13 巻頁： 343 - 346 2015年6月

出版者・発行元：e-Journal of Surface Science and Nanotechnology

The hydrogen absorption behavior of the Pd NPs has been investigated by the noble techniques. The Pd NPs with the clean surface have been fabricated by the gas evaporation method. The P-C isotherm of the hydrogen absorption of the Pd NPs has been obtained using the QCM without the exposure to the air. The P-C isotherms have shown the clear size dependent absorption behavior for the Pd NPs. Further absorption and desorption cycles decrease the solubility of H significantly in the Pd NPs.

DOI： 10.1380/ejssnt.2015.343

Spectroscopic investigation of the chemical state of the hydrogen storage materials composed of the metal nanoparticles

Ogawa S., Uchiyama N., Fujimoto T., Kanai T., Yagi S.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals 79 巻 ( 3 ) 頁： 118 - 123 2015年3月

出版者・発行元：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

We introduce the spectroscopic investigation of the nano-composite materials consisted of Mg and Pd. Mg is most promising material for the application of the hydrogen storage because of the high gravimetric hydrogen storage capacity up to 7.6 mass%. In spite of the advantage of the hydrogen storage capacity, the practical use of Mg has not been established due to the slow hydro-/dehydrogenation reactions and the high temperature required to store and release the hydrogen. Nano-sized Mg such as Mg nanoparticle is expected to store the hydrogen rapidly because of the high specific surface area of the nanoparticle. Moreover, addition of Pd decreases the temperature for the hydrogen storage of Mg because of the catalytic effect for the dissociation reaction of hydrogen molecules. We have fabricated the nanoparticles composed of the both Mg and Pd by the gas evaporation method using He gas. These nanoparticles can store the hydrogen at the room temperature. After the storage of the hydrogen, the release of the hydrogen has not been observed up to 100°C. The analyses of the X-ray absorption fine structure (XAFS) have revealed that the irreversible change of the chemical state during the hydrogen storage causes the inactivation of the surface of nanoparticles and inhibits the dehydrogenation reaction of the MgH2.

DOI： 10.2320/jinstmet.JC201409

Vulcanization reaction of squalene and S-8 powder studied by Sulfur K-edge NEXAFS under liquid phase

Yagi S., Menjo Y., Tsukada C., Ogawa S., Kutluk G., Namatame H., Taniguchi M.

INTERNATIONAL CONFERENCE ON SOLID FILMS AND SURFACES (ICSFS 2014) 76 巻 ( 1 ) 2015年

記述言語：日本語出版者・発行元：IOP Conference Series: Materials Science and Engineering

Vulcanized rubber materials are useful in our surroundings. However, detail structure and reaction are not revealed even in present. Since squalene molecule possesses some same properties compared with natural rubber, we have prepared the samples of vulcanized squalene at 140 ° C for several hours. To understand the vulcanization reaction,sulfur K-edge NEXAFS measurements have been carried out for the vulcanized squalene under liquid phase with He-path system and fluorescence detection mode. Moreover, we have tried curve fitting analysis of NEXAFS spectra. The results indicate that the squalene has been vulcanized by the S8 molecule at 140 ° C and the S8 molecule length is shortened from 8 to 5-6 after the vulcanization reaction.

DOI： 10.1088/1757-899X/76/1/012004

Spectroscopic and morphological studies on interaction between gold nanoparticle and liposome constructed with phosphatidylcholine

Tsukada C., Tsuji T., Matsuo K., Nomoto T., Kutluk G., Sawada M., Ogawa S., Yoshida T., Yagi S.

INTERNATIONAL CONFERENCE ON SOLID FILMS AND SURFACES (ICSFS 2014) 76 巻 ( 1 ) 2015年

記述言語：日本語出版者・発行元：IOP Conference Series: Materials Science and Engineering

The gold nanoparticles (Au NPs) colloidal solution and the phosphatidylcholine (PC) liposome aqueous solution are fabricated by the solution plasma method and the extrusion procedure, respectively. When the Au NPs colloidal solution and the PC liposome aqueous solution are mixed, considering the TEM image, we think that the Au NPs firstly are covered with the PC molecules, which do not contribute to form the PC liposome, and subsequently the Au NPs covered with the PC adsorb on the PC liposome surface. We propose that the PC molecule adsorbs on the Au sheet surface at the methyl group of N-CH3 and the oxygen atoms of P-O, P=O, C-O and C=O bonds, because each peak intensity of N, O and P K-edges NEXAFS spectra for the PC/Au sheet is reduced in comparison with that for the PC multilayer. Furthermore, the Au NPs covered with PC seem to be aggregated each other through the hydrophobic groups of PC on Au NPs.

DOI： 10.1088/1757-899X/76/1/012001

Hydrogen storage property of Ni nanoparticles fabricated by the gas evaporation method

Fujimoto, T; Ogawa, S; Yoshida, T; Uchiyama, N; Yagi, S

SURFACE AND INTERFACE ANALYSIS 46 巻 ( 12-13 ) 頁： 1121 - 1124 2014年12月

記述言語：日本語出版者・発行元：Surface and Interface Analysis

We have fabricated the Ni nanoparticles with a clean surface by the gas evaporation method and clarified the hydrogen storage property by using atomic forcemicroscope (AFM), X-ray photoelectron spectroscopy (XPS) and quartz crystal microbalance(QCM)measurements. The diameter has been estimated as 4.0 ± 1.5nm by AFM observation. The Ni nanoparticles possess a clean surface, because the surface chemical state has been confirmed asmainlymetallic state by XPS. The hydrogen storage property has been investigated by QCM fromthe vacuum to the atmospheric pressure of the hydrogen at 300 K. The plateau pressure of the Ni nanoparticles and amaximum hydrogen storage capacity are about 7 Torr and H/Ni = 0.56, respectively. And the hydrogen release from the Ni nanoparticles has not been observed by QCM. The hydrogen adsorption/desorption reaction have also been observed as the plateau like pressure by QCM. These results indicate that (i) the plateau pressure of Ni is decreased by the nanosizing of the material, (ii) the large specific surface area of the Ni nanoparticlesmakes it possible to observe the adsorption/desorption reaction and (iii) the Ni hydride is stable under the vacuum condition. The chemical shift of Ni 2p3/2 has not been observed in the XPS spectrum between before and after exposure to the hydrogen. This result implies that there is no strong chemical bonding between Ni and hydrogen or the hydrogen in the lateral surface has been released.

DOI： 10.1002/sia.5566

The inuence of the preparing method of a Ag/Ga<inf>2</inf>O<inf>3</inf> catalyst on its activity for photocatalytic reduction of CO<inf>2</inf> with water

Yamamoto N., Yoshida T., Yagi S., Like Z., Mizutani T., Ogawa S., Nameki H., Yoshida H.

e-Journal of Surface Science and Nanotechnology 12 巻頁： 263 - 268 2014年6月

出版者・発行元：e-Journal of Surface Science and Nanotechnology

We have prepared silver-loaded gallium oxide (Ag/Ga2O 3) photocatalysts by the solution plasma method (SPM) and impregnation method (imp), and investigate the effects of the chemical states and the size of the Ag nanoparticles on their photocatalytic activities. The photocatalytic reduction of CO2 with water proceeds over all the Ag/Ga2O3 photocatalysts to produce CO, however the CO production rates decrease during photocatalytic reaction. Measurements of UV-VIS diffuse reflectance spectra, XANES spectra and TEM images reveal the followings: the Ag oxide nanoparticles in the as-prepared Ag/Ga 2O3 (imp) samples exist and their size distribution is wide from 5 to 10 nm. They become a lot of metallic nanoparticles by UV light-irradiation, and become larger particles with the size of ca. 20 nm during the photocatalytic reaction. On the other hand, the Ag nanoparticles in the as-prepared Ag/Ga2O3 (SPM) samples are metallic with the size of less than 10 nm. The size does not change under UV light irradiation, while become larger particles during the photocatalytic reaction as similar to the case of the Ag/Ga2O3 (imp) samples. Such small metallic Ag nanoparticles with the size of 5-10 nm are suitable for CO production. However, they aggregate during the reaction for 5 h to degrade the photocatalytic activity. © 2014 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2014.263

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