受賞国：日本国

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Surface Science  

Helium (He)-induced nanostructured tungsten sheets were synthesized by He plasma irradiation under different plasma exposure durations. After calcination, nanostructured tungsten oxide samples were used as photoelectrodes to test photoelectrochemical (PEC) performance. The results showed that nanostructured WO3 photoanodes have higher PEC performance compared to the sample without nanostructures. The 15 min irradiated sample had the highest photocurrent density of 3.5 mA/cm2 under the thermodynamic potential of water oxidation (1.23 V vs. RHE). It was found that the oxide layer thickness and exposed crystal facet have a significant impact on PEC performance. The plasma synthesis technique has proved to be an effective method for preparing nanostructured WO3 photoelectrodes.

DOI： 10.1016/j.apsusc.2021.151979

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掲載種別：研究論文（学術雑誌）   出版者・発行元：New Journal of Chemistry  

Metal sulfides are promising visible-light photocatalysts for CO2 reduction. However, available sulfide photocatalysts are limited because of their instability in aqueous solutions under photoirradiation. In this study, we investigated the fabrication of a stable CdS photoanode for CO2 reduction. The CdS photoanode prepared by the chemical bath deposition method was subjected to N2 calcination, which significantly affected its stability. Calcination up to 300 °C did not significantly change the surface morphology of the CdS photoanode. In contrast, the CdS electrode calcined at 400 °C had a smoother surface, with a lower surface area of the electrode, which consequently reduced the CdS photocorrosion. K2Cd[Fe(CN)6] (particle size ∼10 nm) was densely formed on the CdS surface via photocorrosion, and it effectively scavenged photogenerated holes in CdS and enabled the oxidation of [Fe(CN)6]4− to [Fe(CN)6]3−. Thus, we demonstrated stable CO2 reduction to CO over the CdS photoanode system in an aqueous solution at an applied bias of 0.5 V vs. Ag counter electrode under visible-light irradiation, along with the oxidation of [Fe(CN)6]4− to [Fe(CN)6]3−

DOI： 10.1039/d1nj06073b

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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：RSC Advances  

We have succeeded in synthesizing meso-porous α-Ga2O3 which shows significantly high photocatalytic activity for CO2 reduction with water. The sample was synthesized by hydroxidation of liquid Ga metal in water to obtain GaOOH and Ga(OH)3, followed by the calcination of the mixed hydroxides at 773 K for 1 hour which converted them to meso-porous α-Ga2O3. The nano-pores remained as the trace of the evaporation of water produced by the oxidation of the hydroxides during the calcination. The photocatalytic activity of the synthesized meso-porous α-Ga2O3 for CO2 reduction with water was as high as or higher than previous studies using various types of Ga2O3 with and without cocatalysts.

DOI： 10.1039/d1ra09039a

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PubMed

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：New Journal of Chemistry  

The photocatalytic activity of mixed phases of GaOOH/β-Ga2O3 and α-Ga2O3/β-Ga2O3 for CO2 reduction with water is investigated for the first time. GaOOH/β-Ga2O3 is synthesized by high energy ball milling of β-Ga2O3 in water, and α-Ga2O3/β-Ga2O3 are prepared by the calcination of GaOOH/β-Ga2O3 at 773 K. Both show higher activity for both CO2 reduction and the accompanying H2 evolution than the original material of β-Ga2O3. This is the first observation that the mixed phase of GaOOH/β-Ga2O3 has high photocatalytic activity. The H2 production rate is correlated to the specific surface area irrespective of the GaOOH/β-Ga2O3 and α-Ga2O3/β-Ga2O3 samples. The CO production rate for the mixed phase of α-Ga2O3/β-Ga2O3 is high, agreeing with the previous observation that the mixed phases or phase boundaries enhance the photocatalytic activity, and the CO production rate increases with the abundance rate of the α-Ga2O3 phase. Although the selectivity of the CO production remains low, it could be enhanced if an Ag cocatalyst was used. As an alternative mechanism of H2 production (H2 evolution) over the samples of GaOOH/β-Ga2O3 and α-Ga2O3/β-Ga2O3, a redox type reaction mechanism is proposed, in which the H2 evolution proceeds with the reduction of GaOOH to α-Ga2O3 emitting H2 and O2 by UV illumination, while α-Ga2O3 returned to GaOOH in water without illumination. Although some of the H2 thus evolved would cause CO2 reduction, CO2 reduction to CO requires specific active sites on the α-Ga2O3 surface.

DOI： 10.1039/d1nj05245d

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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：公益社団法人 日本表面真空学会  

To prepare photocatalysts promoting water splitting under visible light irradiation, GaOOH was nitrided by the calcination at a temperature ranging from 773 to 1273 K under a NH3 flow to produce nitrogen doped Ga2O3. X-ray diffraction measurements suggested that even under NH3 atmosphere dehydration of GaOOH to α-Ga2O3 occurred by calcining below 873 K. In the samples nitrided above 973 K, gallium nitride (GaN) phase started to appear and the crystallinity became better with increasing the nitriding temperature. In diffuse reflectance ultraviolet-visible measurements, absorption bands appeared in the visible light region after the nitrization, and the shift of the absorption edge with nitriding temperature suggested the formation of a new phase like gallium oxy-nitride. X-ray photoelectron spectroscopy and scanning transmission electron microscopy-electron energy-loss spectroscopy analyses revealed that oxygen atoms were distributed homogeneously and mixed with nitrogen atoms in the sample nitrided at 1173 K [referred as S(1173 K)] while oxygen atoms were mainly distributed at the surface of the sample nitrided at 1273 K [S(1273 K)]. The differences in the composition and chemical state near the sample surface closely related to the activity and stability during water splitting reaction under visible light irradiation between S(1173 K) and S(1273 K), i.e., the former sample provided stable H2 and O2 evolution while the latter sample was inactive and unstable.

DOI： 10.1380/ejssnt.2022-003

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CiNii Research

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 Omega  

In order to understand the photocatalytic carbon dioxide reduction over Ag-loaded β-Ga2O3 photocatalysts, first principles calculations based on density functional theory were performed on the surface model of a Ag cluster-adsorbed β-Ga2O3 system. The stable adsorption structures of Agn (n = 1 to 4) clusters on the β-Ga2O3 (100) surface were determined. In the electronic structure analysis, the valence states of all Ag clusters mixed with the top of the O 2p valence band of Ga2O3, leading the Fermi level of Agn/β-Ga2O3 to shift to the bottom of the conduction band. It was also revealed that the unoccupied states of Agn clusters overlapped with the Ga unoccupied states, and occupied electronic states of Ag clusters were formed in the band gap. These calculation results corresponded to the experimental ones obtained in our previous study, i.e., small Ag clusters had strong interaction with the Ga2O3 surface, enhancing the electron transfer between the Ag clusters and the Ga2O3 surface. That is, excited electrons toward Agn clusters or the perimeter of Ag-Ga2O3 should be the important key to promote photocatalytic CO2 reduction.

DOI： 10.1021/acsomega.1c04730

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Catalysis Today  

Ag loaded Ga2O3 photocatalysts are well known to be highly active for the CO2 reduction with water to CO. However, Ag changes its chemical state during the reaction, resulting in the decrease of its photocatalytic activity. To examine the chemical state change during the photocatalytic CO2 reduction, we have attempted a real time observation of the change in the chemical and physical states of Ag co-catalyst loaded on Ga2O3 by monitoring UV–vis reflectance spectra under the atmosphere simulating the photocatalytic CO2 reduction. In UV–vis spectra, two characteristic absorptions appeared at around 450 nm and 600 nm corresponding to resonance absorptions of localized surface plasmon (LSPR) of Ag nanoparticles (Ag-NPs) and Ag in metallic state. The LSPR absorption appeared as light irradiation started and grew with the time. It was revealed that Ag on Ga2O3 was initially in the oxidized state and reduced by the light irradiation to be Ag-NPs. Further light irradiation enlarged the size of Ag-NPs to be the metallic state especially under atmosphere with water. Under CO2 atmosphere, Ag-NPs remained small after further light irradiation. These results suggest that Ag initially loaded on Ga2O3 in the oxidized state was reduced to be dissolved as Ag+ in water and precipitated as Ag-NPs. Then, some of Ag-NPs aggregated to be larger Ag particles or in the metallic state. Such reduction process depends on gas species of the system, i.e. water promoted the formation of Ag-NPs while CO2 suppressed the formation Ag-NPs.

DOI： 10.1016/j.cattod.2020.04.063

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

In order to realize high-performance titanium dioxide (TiO2) photocatalysts for ethylene decomposition, titanium (Ti) thin film samples with fiberform nanostructures were prepared by helium (He) plasma treatment. Then, the oxidation condition for ethylene decomposition were optimized in terms of the oxidation temperature and duration. It is shown that He plasma irradiation with Ti deposition followed by oxidation in the air formed anatase-rich TiO2. The rutile anatase transition temperature increased to higher than 1000 K on the He treated samples and the best photocatalytic performance is twice higher than that on TiO2 sample formed in a magnetron sputtering device. Helium plasma treatment induces vacancies, He clusters, and He bubbles together with formation of nanostructures. The results suggested that those morphology changes lead to the formation of stable anatase structure, which is likely the key factor for the enhancement of photocatalytic activity. Based on the obtained ethylene decomposition rate, we will discuss the necessary light source and amount of photocatalysts to keep vegetables fresh in a long-distance transport cargo.

DOI： 10.1016/j.jphotochem.2021.113420

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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 Omega  

We have succeeded to synthesize gallium oxide consisting of α-phase (α-Ga2O3) with the calcination of GaOOH obtained by a direct reaction of liquid Ga metal with water for the first time and found that α-Ga2O3 exhibits photocatalytic activity for CO2 reduction with water and water splitting as well. The calcination above 623 K converted GaOOH to α-Ga2O3, and the samples calcined at 723-823 K were well crystallized to α-Ga2O3 and promoted photocatalytic CO2 reduction with water, producing CO, H2, and O2. This is observed for the first time that α-Ga2O3 without a cocatalyst has shown very high photocatalytic activity for the conversion of CO2 to CO.

DOI： 10.1021/acsomega.1c02088

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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  

NaTaO3, a semiconductor with a perovskite structure, has long been known as a highly active photocatalyst for overall water splitting when appropriately doped with La cations. A profound understanding of the surface feature and why and how it may control the water splitting activity is critical because redox reactions take place at the surface. One surface feature characteristic of La-doped NaTaO3is a La-rich layer (shell) capping La-poor bulk (core). In this study, we investigate the role of the shell in core-shell-structured La-doped NaTaO3through systematic chemical etching with an aqueous HF solution. We find that the La-rich shell plays a role in electron-hole recombination, electron mobility and water splitting activity. The shallow electron traps populating the La-rich shell trap the photoexcited electrons, decreasing their mobility. The shallowly trapped electrons remain reactive and are readily available on the surface to be extracted by the cocatalysts for the reduction reaction evolving H2. The presently employed chemical etching method also confirms the presence of a La concentration gradient in the core that regulates the steady-state electron population and water splitting activity. Here, we successfully reveal the nanoarchitecture-photoactivity relationship of core-shell-structured La-doped NaTaO3that thereby allows tuning of the surface features and spatial distribution of dopants to increase the concentration of photoexcited electrons and therefore the water splitting activity. By recognizing the key factors that control the photocatalytic properties of a highly active catalyst, we can then devise proper strategies to design new photocatalyst materials with breakthrough performances.

DOI： 10.1039/d1cp00375e

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記述言語：日本語   出版者・発行元：公益社団法人 日本分析化学会　X線分析研究懇談会  

DOI： 10.57415/xshinpo.52.0_261

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Surface Science  

Since the activity of semiconductor photocatalysts for CO2 reduction with water is still low, it is necessary to improve their activity. To do this, the optimization of particle size and crystal structure of the photocatalysts is one of the promising ways. In previous studies, we have reported that micro-particulate Ga2O3 deposited on Al2O3 support significantly improves the photocatalytic activity of CO2 reduction. However, it is quite difficult to synthesize nano-particulate Ga2O3 with high crystallinity by calcination at higher temperatures. In this work, we have tried to synthesize sheet-like nano-particulate Ga2O3 using graphene oxide (GO) as a template for the first time. After loading gallium butoxide on GO, it was calcined to oxidize the gallium butoxide into Ga2O3 and also to remove GO. Various spectroscopic analyses revealed that the synthesized materials were planar aggregation of nanometer-sized Ga2O3 particles (nsGa2O3), of which sizes and crystallinity could be controlled with the calcination temperature. The nsGa2O3 calcined at 1123 K was well crystallized and showed β-phase with a quite large specific surface area. Furthermore, Ag loaded nsGa2O3 calcined at 1123 K (Ag/nsGa2O3(1123 K)) showed very high photocatalytic activity for CO production in the photocatalytic CO2 reduction test in water including methanol under UV light irradiation. Thus, it is confirmed that the planar aggregation of nanometer-sized Ga2O3 significantly improves the photocatalytic activity of Ga2O3 on the CO2 reduction.

DOI： 10.1016/j.apsusc.2020.148680

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Nanophotonics  

To reduce the effects of global warming, visible and near-infrared light must be used more efficiently. Deep ultraviolet light (8 eV) is required for the direct dissociation of CO2 by light; however, the introduction of a metal complex has made it possible to realize CO2 reduction with visible light. We demonstrate that the optical near field (ONF) can increase the CO2 reduction rate. For this, we used gold clusters, because they can be a suitable source for ONFs, as their size and density can be controlled by the number of gold atoms. By attaching a metal complex near gold clusters with diameters of 1.0 to 1.3 nm, we confirm that the reduction rate of CO2 to CO increased by 1.5 to 2.1 times. The gold clusters were sufficiently small; therefore, there was no plasmonic resonant peak or heat generation. Because the near-field effect is based on a photochemical reaction, it can be applied to other metal complexes used in CO2 reduction, and it has other applications such as water splitting and water purification.

DOI： 10.1117/1.JNP.14.046011

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

We found the mineralization of Cu during long-term Cu2+ adsorption onto dry baker’s yeast cells phosphorylated using sodium cyclo-triphosphate. Field emission scanning electron microscopy (FESEM) with energy-dispersive X-ray spectroscopy confirmed that the elemental composition of minerals were copper, phosphorus, and oxygen. Synchrotron-based X-ray absorption fine structure showed that the local structure around Cu atoms deposited on the mineral was almost identical to that of commercial copper (II) phosphate Cu3(PO4)2 3H2O. However, the crystallinity was low, and the structure was slightly distorted. Time profile analysis using FESEM revealed that copper phosphate mineralization was first apparent on Day 3 of adsorption, whereas mineral formation plateaued at around Day 7. It seems that mineralization occurs by the local saturation of phosphate and Cu2+ on the yeast cells. Mineralization of the rare earth ion Dy3+ was also demonstrated during long-term adsorption. Mineralization on phosphorylated yeast cells appears to follow a common path for various types of metal ions and provides a promising technique for metal recovery via irreversible adsorption.

DOI： 10.1371/journal.pone.0239774

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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   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

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

Understanding the science behind highly active materials is essential for advancement in the field of photocatalytic water splitting for solar energy harvesting. Sodium tantalate (NaTaO3) doped with La cations is one of the best engineered materials for efficient water splitting to evolve hydrogen. In this study, physical insights into the sensitivity of the water-splitting activity to the spatial La distribution are discussed. The spatial distribution of La cations placed at the Na site was found to dictate the energy gradient of the conduction band bottom (CBB), resulting in a tunable electron population and hence water-splitting activity. A less homogeneous sample with a sufficiently large CBB gradient exhibited higher water-splitting activity. The mechanism of gradient tuning of the CBB through controlling the spatial dopant distribution is expected to be applicable to a broad range of metal oxide perovskites for artificial photosynthesis.

DOI： 10.1021/acs.jpcc.0c03822

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Materials Research Express  

Helium-plasma irradiation induces nanostructure formation on metal surfaces. This study investigated the photocatalytic performance of tungsten (W) oxide nanostructures formed on a thin film and the loading effects of noble metals. Methylene blue (MB) degradation was performed, and the performance of different nanostructured samples formed on thin-film and sheet W with changing the oxidization temperatures was compared; the differences were discussed in terms of the oxidation degree and vacancies. Moreover, noble metals (Pt, Ag, Au) were loaded onto the nanostructured sample oxide by magnetron sputtering as cocatalysts. The MB degradation ability was significantly enhanced by Pt loading. The results showed that nanostructuring and Pt support by using dry processes are novel routes for fabricating highly active photocatalysts.

DOI： 10.1088/2053-1591/aba394

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その他リンク： https://iopscience.iop.org/article/10.1088/2053-1591/aba394/pdf

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：公益社団法人 日本化学会  

DOI： 10.1246/bcsj.20190366

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CiNii Research

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：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

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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：公益社団法人 日本表面真空学会  

It is well known that Ag loaded Gallium oxide (Ag/Ga2O3) promotes photocatalytic CO2reduction to CO. However, the role of the Ag co-catalyst in the CO2reduction has not been clarified. We have intended to find the relationship between the state of Ag loaded on Ga2O3and their activity for the photocatalytic CO2reduction. To achieve this, we have tried to control and stabilize the loading state of Ag on Ga2O3during their use for the photo-catalytic CO2reduction by adding methanol as a reducing agent. It is confirmed that methanol stabilizes the particle sizes of Ag nanoparticles (Ag-NPs) loaded on Ga2O3under the photocatalytic CO2reduction condition and is hardly decomposed to produce CO. Using Ga2O3loaded with size-controlled Ag-NPs as a photocatalyst for the CO2reduction, it is found that Ag-NPs with their sizes within 10-30 nm are active sites for the photocatalytic CO2reduction and the catalytic activity linearly increases with the increase of the number density of Ag-NPs. However, a higher Ag loading amount over 1.0 wt% promotes aggregation of Ag to be larger metal particles over 70 nm which are not active for the CO2reduction. (Figure Presented).

DOI： 10.1380/ejssnt.2020.168

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CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry A  

We have succeeded in synthesizing black phosphorus (BP) by a one-pot solvothermal reaction of red phosphorus (RP) and ethylenediamine (ED) used as a solvent. To examine the reaction mechanism, we have investigated the influence of the synthesis conditions on BP, and the valence of dissolved phosphorus in the solvent after the reaction. P0 species and P3+ like species are very likely dissolved in ED as intermediates for BP production. Optimizing the reaction conditions, i.e., temperature, the charging amount of RP in ED and the particle size of RP, BP was synthesized with high yield. The synthesized BP has an extra peak at 10.2° in the X-ray diffraction pattern, which was assigned to stacking faults or periodic distortion in the direction of the c axis by simulation of diffraction. The synthesized BP with a Co-P cocatalyst showed high photocatalytic activity for hydrogen evolution from methanol aqueous solution under visible light irradiation.

DOI： 10.1039/c9ta13441g

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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：公益社団法人 日本表面真空学会  

We have prepared La2O3supported Ga2O3(Ga2O3/La2O3) photocatalyst to improve the photocatalytic activity of Ga2O3for CO2reduction with water under ultraviolet light irradiation without a noble metal cocatalyst. Significant improvement on both CO2reduction and water splitting was attained compared with those for non-supported Ga2O3and La2O3. The improve-ment is attributed to the transformation of the La2O3surface to NaLa(CO3)2 during the photocatalytic reduction tests in aqueous solution of NaHCO3. NaLa(CO3)2 was preferentially formed on the surface of La2O3without changing Ga2O3resulting in the structure of Ga2O3supported by NaLa(CO3)2. Once NaLa(CO3)2 fully covered the surface of La2O3, the high catalytic activity was kept long. (Figure Presented).

DOI： 10.1380/ejssnt.2020.110

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CiNii Research

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Catalysis B: Environmental  

Ga2O3 samples were synthesized by calcination of gallium nitrate powder at a given temperature ranging from 673 K to 1173 K (denoted as T-Ga2O3 with T, calcination temperature). XRD and XAFS structural analyses revealed that samples calcined at temperatures below 673 K were consisted of defective ε phase, whereas those calcined above 773 K of β and γ phases, and β phase dominated above 923 K. All calcined Ga2O3 samples promoted photocatalytic CO2 reduction with water to produce CO, H2 and O2. As for the H2 production by water splitting, the H2 production rates were well correlated with the surface areas of calcined Ga2O3 samples. It was also found that the water splitting and the CO2 reduction proceeded fully independently. 823-Ga2O3 showed the highest activity for the CO2 reduction, suggesting that the coexistence of β and γ phases plays a key role on the photocatalytic CO2 reduction.

DOI： 10.1016/j.apcatb.2019.118247

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

In this study, two photosensitive nanostructured photocatalysts (i.e. a nanostructured W sheet (WNano) and a nanostructured W thin film (WNTF), respectively) were fabricated by helium plasma irradiation. In addition, the photocatalytic activity was examined for the degradation of methylene blue under visible light irradiation. The result revealed that the highest photocatalytic activity is observed for WNano subjected to calcination at 573 K. The difference in the photocatalytic activities between WNano and WNTF was possibly caused by the difference in the surface area and the presence of a W/WO3 interface. Among the series of the WNano photocatalysts subjected to calcination at different temperatures, the localized surface plasmon resonance of nanostructured W was likely responsible for photocatalysis.

DOI： 10.7567/1347-4065/ab4601

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その他リンク： http://iopscience.iop.org/article/10.7567/1347-4065/ab4601/pdf

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 Omega  

We have studied degradation of photocatalytic activity of TiOxNy for water splitting under visible light irradiation with heat treatment in O2/N2 mixed gas. The reduction of the N content by oxidation through the formation of O-N-O species (NOx) was confirmed as the result of the reduction of the catalytic activity. The catalytic activity is not simply related to the amount of N remained but that of N taking the chemical state of O-Ti-N in TiOxNy, which is the active species for visible light responsiveness on hydrogen evolution. N in TiOxNy is first oxidized to NO2 species during the oxidation, which reduces the activity. Then, O-N-O species (NOx) is removed as NOx gas from the surface. Because the formation of O-N-O in TiOxNy could induce an impurity energy level to enhance charge recombination, the loss of catalytic activity might be influenced by the formation of O-N-O species (NOx) rather than the loss of the N content from TiOxNy.

DOI： 10.1021/acsomega.9b02979

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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 Omega  

TiOxNy/TiO2 was synthesized by nitriding of TiO2 in NH3 gas. TiOxNy/TiO2 generated hydrogen from methanol aqueous solution under visible-light irradiation. It was revealed by N K-edge XANES and N 1s XPS measurements that the N species contributing to visible-light responsiveness was the O-Ti-N species. The structure of TiOxNy/TiO2 showing the photocatalytic activity was a double shell type with thin layers of TiOxNy that covers the TiO2 core. Although N content on the surface decreased during the photocatalytic reaction, N was supplied from the deeper side to keep the TiOxNy phase at the surface and the activity as well.

DOI： 10.1021/acsomega.9b02977

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Angewandte Chemie - International Edition  

A chiral composite material, derived from the deposition of a chiral nickel–diamine complex via wet impregnation to MCM-41, was shown to be an efficient heterogeneous catalyst for asymmetric 1,4-addition reactions of 1,3-dicarbonyl compounds with nitroalkenes, and of nitromethane with alkylidenemalonates. It was discovered that MCM-41 enhanced the reactivity and improved the stability of the chiral nickel complex that resides within the mesoporous material.

DOI： 10.1002/anie.201906349

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.201906349

掲載種別：研究論文（学術雑誌）   出版者・発行元：Nanotechnology  

In many applications such as CO2 reduction and water splitting, high-energy photons in the ultraviolet region are required to complete the chemical reactions. However, to realize sustainable development, the photon energies utilized must be lower than the absorption edge of the materials including the metal complex for CO2 reduction, the electrodes for water splitting, because of the huge amount of lower energy than the visible region received from the sun. In the previous works, we had demonstrated that optical near-fields (ONFs) could realize chemical reactions, by utilizing photon energies much lower than the absorption edge because of the spatial non-uniformity of the electric field. In this paper, we demonstrate that an ONF can realize the red shift of the absorption spectra of the metal-complex material for photocatalytic reduction. By attaching the metal complex to ZnO nano-crystalline aggregates with nano-scale protrusions, the absorption spectra by using diffuse reflection of the metal complex can be shifted to a longer wavelength by 10.6 nm. The results of computational studies based on a first-principles computational program including the ONF effect provide proof of the increase in the absorption of the metal complex at lower photon energies. Since the near-field assisted field increase improves the carrier excitation in the metal-complex materials, this effect may be universal and it could applicable to CO2 reduction using the other metal-complex materials, as well as to the other photo excitation process including water splitting.

DOI： 10.1088/1361-6528/ab2092

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PubMed

その他リンク： http://iopscience.iop.org/article/10.1088/1361-6528/ab2092/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：Green Chemistry  

Alkene hydrosilylation is important for the synthesis of organosilicon compounds, for which precious metal complexes have been used as industrial catalysts. Considering environmental and economic concerns, the development of earth-abundant metal catalysts with high stability, easy separability, and high reusability is strongly desired. Herein, we report that a new cobalt ion-doped titanium dioxide (Co/TiO2) catalyst was synthesized by hydrogen treatment method. The Co/TiO2 catalyst acts as a highly efficient heterogeneous catalyst for the anti-Markovnikov hydrosilylation of alkenes under solvent-free conditions. Various alkenes were selectively converted to the corresponding alkylsilanes. This catalyst showed high stability in air and high reusability with maintained activity. The investigation of the relationship between the active site structure and catalytic performance of Co/TiO2 disclosed that the high stability and durability of Co/TiO2 are originated from the strong interaction between Co and TiO2 through the formation of CoTiO3 solid solution species.

DOI： 10.1039/c9gc01981b

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Catalysis B: Environmental  

We have performed dehydronitrization of GaOOH under NH3 flow to produce nitrogen doped Ga2O3 and examined their photocatalytic activities for H2 evolution from an aqueous methanol solution under visible light irradiation. GaOOH was synthesized by hydrothermal treatment and dehydronitrided at a temperature ranging from 773 K to 1273 K under NH3 flow. At first, GaOOH was dehydrided to Ga2O3 under 873 K and followed nitrization. With increasing dehydronitrization temperature, the products were getting closer to full nitride (GaN). Among all dehydronitrided samples, only one sample sintered at 1173 K showed photocatalytic activity under visible light irradiation and its crystalline structure had not changed before and after the reactions, while other samples did not show the activity and were oxidized to GaOOH. From thermodynamical aspect, if nitrogen dissolved into oxide or making oxynitride, its chemical potential must be lower than that of N in GaN. Therefore, there should be some gallium oxinitride phase like GaNyO3-x stable in water showing photocatalytic activity.

DOI： 10.1016/j.apcatb.2019.03.009

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

KTaO3 was doped with Sr cations, and its photocatalytic activity for the overall water splitting was investigated. By doping with Sr, a Sr-rich shell was formed over a Sr-poor core. Extended X-ray absorption fine structure spectroscopy revealed the simultaneous occupation of the K sites and Ta sites by Sr cations. A concentration gradient of Sr cations occupying the Ta sites was suggested to be produced after doping with Sr. The concentration gradient of Sr cations simultaneously induced an energy gradient of the conduction band edge bottom. Hence, photoexcited electrons are separated, which are driven away to the bulk by the energy gradient, from the complementary holes present on the surface. The higher the Sr cation concentration, the higher the energy gradient produced. Thus, the electron-hole separation is improved and the electron population accordingly increases with the increase in the Sr cation concentration. Nevertheless, the increase in the Sr cation concentration led to the decrease in the water splitting activity. The highest water splitting activity was observed for bare KTaO3. The decreased water splitting activity was proposed to be primarily due to the blockage of the electron transfer to the cocatalysts by the Sr-rich shell and the poor O2 evolution ability of the Sr-rich shell.

DOI： 10.1021/acs.jpcc.9b03640

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemistry Letters  

Selective hydrogen production from formic acid with platinum nano-cluster dispersed by various protective polymer based agents polyvinylpyrrolidone (Pt-PVP) or polyacrylic acid (Pt-PAA) is attempted. The ratio of hydrogen to CO2 was estimated to be c.a. 1.0 (stoichiometric ratio) under the argon-saturated buffer solution containing formic acid with Pt-PVP.

DOI： 10.1246/cl.190311

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掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

DOI： 10.7567/1347-4065/ab2830

その他リンク： http://iopscience.iop.org/article/10.7567/1347-4065/ab2830/pdf

掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

DOI： 10.7567/1347-4065/ab09c8

その他リンク： https://iopscience.iop.org/article/10.7567/1347-4065/ab09c8

掲載種別：研究論文（学術雑誌）   出版者・発行元：Chemical Physics Letters  

We have investigated chemical forms of molybdenum ion in nitric acid solution, using liquid-phase X-ray absorption fine structure, ultraviolet–visible absorption spectroscopy and first-principles calculations, from a viewpoint of disposal of high-level radioactive nuclear liquid wastes. The experimental and theoretical results indicated that Mo is a hexavalent ion and forms a hexa-coordination binuclear-structured complex in the 2 M nitic acid solution. The predominant chemical species of Mo complexes in the 2 M nitric acid solution (which is used for HLLW) are assigned to be [Mo2O5(H2O)6]2+ and [Mo2O4(OH)(H2O)6]3+. These species may play a crucial role of forming so-called yellow-phase in vitrified objects.

DOI： 10.1016/j.cplett.2019.02.049

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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 Omega  

We have examined the photocatalytic activity of Ga 2 O 3 supported on Al 2 O 3 (Ga 2 O 3 /Al 2 O 3 catalyst) without a noble metal cocatalyst for water splitting and reduction of CO 2 with water under UV light irradiation by changing the loading amount of Ga 2 O 3 . All prepared Ga 2 O 3 /Al 2 O 3 catalysts show photocatalytic activities for both water splitting and CO 2 reduction, and their activities are significantly improved compared to those of nonsupported Ga 2 O 3 and Al 2 O 3 . The water splitting is dominated for Ga 2 O 3 /Al 2 O 3 with less than 1.0 vol % of Ga 2 O 3 loaded, whereas the CO 2 reduction, for higher Ga 2 O 3 -loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga 2 O 3 /Al 2 O 3 catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga 2 O 3 rods dispersed on an Al 2 O 3 support consisting of a little distorted α-Ga 2 O 3 phase. On the other hand, the CO 2 reduction proceeds on sub-micrometer-sized Ga 2 O 3 particles consisting of mixed phases of α-Ga 2 O 3 and γ-Ga 2 O 3 or with appearance of boundaries between the α and γ phases, which plays a critical role. Al 2 O 3 used as the support of the Ga 2 O 3 particles does not seem to play an important role in the photocatalytic CO 2 reduction.

DOI： 10.1021/acsomega.9b00048

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PubMed

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

With a view to rational designing of a highly functional visible-light TiO2 photocatalyst, nitrogen atoms were doped into TiO2 samples by an ion implantation technique which enables to control the depth and concentration of dopants. Although the absorbance in the visible-light region of the sample increased by the nitrogen doping, photocatalytic activity of the sample was not directly connected with the photo-absorbance. The N K-edge X-ray absorption near edge structure (XANES) spectrum of the photocatalytic active sample (A-cat) showed a characteristic double peak at 398 and 401 eV, and the XANES spectrum of the inactive sample (I-cat) a distinct single peak around 401 eV. These features of the XANES spectra were well reproduced by theoretical simulations based on the model where an O atom in TiO2 was replaced by N ((N)s) for A-cat, and that of quasi NO2 molecule ((NO2)s) for I-cat. Therefore, we have concluded that the nitrogen atom occupying the oxygen site of TiO2 is photocatalytic active species effective for visible light photocatalysis. In addition, the quantitative XANES/ELNES analysis has revealed that the photo-absorbance ratio of I-cat to A-cat corresponds well to the ratio of total doped nitrogen concentration rather than photocatalytic active nitrogen ((N)s) concentration. This result indicates that not only (N)s but also (NO2)s also absorb the visible light. Thus, the absorbance in the visible-light region is not necessarily an indication of the visible-light response of a photocatalyst.

DOI： 10.1002/sia.6543

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO2 reduction with water. Among all the prepared Ag-loaded metal oxides, Ga2O3, ZrO2, Y2O3, MgO, and La2O3 showed activities for CO and H2 productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d0, d10, and s0 had the potential for CO2 reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO2 adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO2 enhanced H2 production rather than CO production due to very little CO2 adsorption. Ag/Ga2O3 exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La2O3, Ag/Y2O3, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H2 production. However, the adsorbed carbonate species were hardly converted to the bidentate formate.

DOI： 10.1002/sia.6542

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

Nitrogen-doped NaTaO3 was synthesized through 1-pot reaction, hydrothermal process using Ta3N5 as precursor. Changing concentration and amount of NaOH aqueous solution influenced nitrogen content in NaTaO3. Absorption edge of nitrogen-doped NaTaO3 was extended at 570 nm, and absorbance in visible light region depended on nitrogen content in NaTaO3. Anodic photocurrent measured under visible light irradiation became larger with increasing nitrogen content in NaTaO3-xNy. Under ultraviolet light irradiation (λ ≤ 400 nm), the highest anodic photocurrent was observed when nitrogen concentration was y = 0.024. It was possible to expand the wavelength range that can be effectively utilized for the photoelectrochemical reaction.

DOI： 10.1002/sia.6556

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

Ga2O3 samples with different crystalline structures were prepared by calcination of a gallium nitrate powder around 800 K. Ga2O3 samples with mixed phases of γ and β showed high photocatalytic activity for CO production from CO2 reduction with water, and the activity was even higher than that for an Ag-loaded β-Ga2O3. The photocatalytic activity increased with time. The increase was attributed to the appearance of GaOOH resulting from the interaction of Ga2O3 with water during the reaction as revealed by XRD and XPS analyses. In situ FT-IR measurements revealed that bicarbonates and bidentate carbonate species were adsorbed on GaOOH. Therefore, the increase of the photocatalytic activity with time would be derived from the formation of GaOOH phase on the γ-Ga2O3 and β-Ga2O3 sample.

DOI： 10.1002/sia.6552

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

Fiberform nanostructured niobium (Nb) was fabricated by one step helium (He) plasma irradiation. He ion implantation formed He nano-bubbles on a Nb plate and led to formation of protrusions while migrating in Nb matrix; fiberform nanostructures (FN) were grown when the fluence became high (>1026 m−2). The necessary conditions for the formation of Nb FN were revealed to be the surface temperature range of 900–1100 K and the incident ion energy higher than 70 eV. The sample was oxidized at 573–773 K in an air atmosphere, and Pt nanoparticles were photo-deposited on the Nb2O5 samples. The surface was analyzed by scanning electron microscope, transmission electron microscope, x-ray photoelectron spectroscopy, and ultraviolet-visible spectrophotometry. Photocatalytic activity of the fabricated materials was studied using methylene blue (MB) decolorization process. An enhanced photocatalytic performance was identified on FN Nb2O5 substrate with Pt deposition.

DOI： 10.1002/cphc.201800769

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

To promote photocatalytic activity of gallium oxides (Ga2O3) on CO2 reduction with water under visible light irradiation, we have tried nitrogen doping into Ga2O3 with different crystalline structures. In diffuse reflectance UV-vis spectra, absorption bands appeared in the visible light region after the nitrogen doping and the absorption edge shifted to a longer wavelength region with increasing nitrogen doping temperature. N K-edge XANES analysis clearly showed two kinds of nitrogen species doped in the samples; gallium nitride (GaN) species and molecular like nitrogen. In XRD patterns, nitrogen doping at temperatures above 823 K, gallium nitride phases appeared while the original crystal structures of gallium oxide samples maintained when nitrogen doping temperature was less than 823 K. However, photocatalytic CO2 reduction under visible light irradiation was insignificant for all the nitrogen doped samples, because nitrogen doped in Ga2O3 samples was unstable in water under the visible light

DOI： 10.1380/ejssnt.2018.262

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CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Physics D: Applied Physics  

Plasma irradiation was used to create nanostructured vanadium oxide with potential commercial and industrial applications. Morphology changes were induced at the nano- and micro-meter scale, accompanied by the growth of helium nanobubbles. Micrometer-sized pillars, cube-shaped nanostructures, and fuzzy fiberform nanostructures were grown on the surface; the necessary conditions in terms of the incident ion energy and the surface temperature for those morphology changes were revealed. Hydrogen production experiments using a photocatalytic reaction with aqueous methanol solution were conducted on the fabricated samples. Enhanced H2 production was confirmed with the plasma irradiated nanostructured sample that had been oxidized in air atmosphere. Photocatalytically inactive vanadium oxide exhibited a high photocatalytic activity after nanostructurization of the surface by helium plasma irradiation.

DOI： 10.1088/1361-6463/aabe44

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その他リンク： http://iopscience.iop.org/article/10.1088/1361-6463/aabe44/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Catalysis Science and Technology  

A Pt-loaded TiO2 photocatalyst successfully catalyzed the direct cross-coupling between various alkenes and tetrahydrofuran (THF) without any additional oxidizing agent. The reaction between cyclohexene and THF gave three cross-coupling products, namely, 2-cyclohexyltetrahydrofuran (A), 2-(cyclohex-2-en-1-yl)tetrahydrofuran (B) and 2-(cyclohex-1-en-1-yl)tetrahydrofuran (C), along with gaseous hydrogen. The mechanistic study revealed that these products were formed through different individual mechanisms: successive addition of two radical species, a 2-tetrahydrofuranyl radical and a hydrogen radical, to the double bond of cyclohexene for A, coupling of a 3-cyclohexenyl radical and a 2-tetrahydrofuranyl radical for B, and 2-tetrahydrofuranyl radical addition and hydrogen radical elimination at the double bond of cyclohexene for C. Among these three mechanisms, those for B and C are dehydrogenative. In this photocatalytic reaction system, since the cyclohexene molecule has enough reactivity, due to the localized π electron density, the Pt nanoparticles loaded on the TiO2 function not as a metal catalyst but as an electron receiver to enhance the charge separation, although the dehydrogenative cross-coupling of benzene with THF requires Pd metal catalysis.

DOI： 10.1039/c8cy00129d

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Photochemistry and Photobiology A: Chemistry  

Ga2O3 prepared by calcination of a gallium nitrate powder showed high activity for CO2 reduction with water to produce CO, and the CO production rate was 150 times that of commercially available Ga2O3 (CA-Ga2O3). Although we also prepared Ag loaded Ga2O3 (Ag/Ga2O3) for further improvement of CO production, the CO production activity decreased by Ag loading on the prepared Ga2O3. On the other hand, CO production was enhanced by Ag loading on CA-Ga2O3. The crystalline structures of the prepared Ga2O3 and CA-Ga2O3 were coexistence of γ- and β- phases of Ga2O3 and single β-phase of Ga2O3, respectively. The crystalline structure of CA-Ga2O3 was maintained after Ag loading with various methods, however, that of the prepared Ga2O3 changed by Ag loading. Therefore, the CO production activity increased by Ag loading depended on the crystalline structure of Ga2O3 supports. In addition, we revealed that Ga2O3 with mixed phases of γ- and β- not loaded with Ag exhibited the highest photocatalytic activity for CO production.

DOI： 10.1016/j.jphotochem.2017.11.010

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Catalysis Today  

Flux method was applied to prepare sodium hexatitanate (Na2Ti6O13) photocatalysts for reduction of carbon dioxide with water. The preparation conditions were examined, such as the starting material, the flux, the composition in the molten mixture, the holding temperature, and the cooling rate of the molten mixture, so as to obtain several sodium hexatitanate samples consisting of the crystals with various morphologies and sizes. These samples were loaded with 0.1 wt% of Ag cocatalyst nanoparticles (Ag/Na2Ti6O13) and examined for photocatalytic reduction of carbon dioxide with water, where carbon monoxide, hydrogen and oxygen were formed as products. It was found that the photocatalytic production rate of carbon monoxide varied with the morphology and the size of the sodium hexatitanate crystals. Among the prepared samples, thick rod-like crystals exhibited high photocatalytic activity for the reduction of carbon dioxide.

DOI： 10.1016/j.cattod.2017.09.029

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Catalysis Today  

Silver nanoparticles (Ag NPs) were synthesized by a solution plasma method (SPM) in an aqueous solution of ammonia. Optical emission spectra of the plasma revealed that Ag NPs are fabricated with the sputtering of Ag rods as electrode by the produced energetic plasma particles such as H, OH and O radicals. In-situ optical absorption measurements of the solution during the discharge directly presented the concerted formation and aggregation processes of the Ag NPs, which controlled the size of Ag NPs. The synthesized Ag NPs were loaded on gallium oxide (Ga2O3) photocatalyst, and the photocatalytic activities of the obtained Ag loaded Ga2O3 (Ag/Ga2O3) samples were evaluated. Although the photocatalytic reaction proceeded over all the samples to produce CO, the CO production rates decreased with the reaction time. Measurements of DR UV–vis spectra and TEM images revealed that a part of the Ag NPs migrated and aggregated on the photocatalyst surface to become larger particles during the photocatalytic reaction, which would be related to the decrease of the photocatalytic activity. It was also found that the photoirradiation treatment on the prepared Ag/Ga2O3 sample before the use for the photocatalytic reaction improves the photocatalytic performance.

DOI： 10.1016/j.cattod.2017.08.047

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Catalysis Today  

Ag species in the Ag loaded Ga2O3 (Ag/Ga2O3) photocatalysts were investigated with regard to changes in their structures and the chemical states before and after the photocatalytic CO2 reduction with water. Ag clusters with the size of around one nanometer in as prepared 0.1 wt% Ag/Ga2O3 sample became larger metallic Ag nanoparticles with the size of several nanometers after the reaction. In the 1.0 wt% Ag/Ga2O3 sample, Ag nanoparticles having the AgGaO2 interface structure decomposed to aggregated Ag metal particles after the reaction. Such transition in the morphology and chemical states of Ag species could explain the variations in photocatalytic activities of these samples during the reaction, and suggested that at least metallic Ag particles would function as effective co-catalysts. In-situ FT-IR measurements of the Ag/Ga2O3 samples before and after the reaction, we could not detect CO2 molecules adsorbing on metallic Ag nanoparticles in dark. Under light irradiation, however, the absorption bands originated from the photo-adsorbed CO2 species on Ag metal nanoparticles appeared. Thus, we detected the interaction of CO2 molecules and metallic Ag nanoparticles as the effective co-catalysts for CO2 reduction.

DOI： 10.1016/j.cattod.2017.09.025

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIP Advances  

We have investigated the chemical forms of palladium (Pd) ion in nitric acid solution, using XAFS/UV-vis spectroscopic and first-principles methods in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW: radioactive metal ions in 2 M nitric acid solution). The results of theoretical calculations and XAFS/UV-vis spectroscopy indicate that Pd is a divalent ion and forms a square-planar complex structure coordinated with four nitrate ions, [Pd(NO3)4]2-, in nitric acid solution. This complex structure is also thermodynamically predicted to be most stable among complexes [Pd(H2O)x(NO3)4-x]x-2 (x = 0-4). Since the overall feature of UV-vis spectra of the Pd complex was independent of nitric acid concentration in the range 1-6 M, the structure of the Pd complex remains unchanged in this range. Furthermore, we examined the influence of γ-ray radiation on the [Pd(NO3)4]2- complex, using UV-vis spectroscopy, and found that UV-vis spectra seemed not to be changed even after 1.0 MGy irradiation. This implies that the Pd complex structure will be still stable in actual HLLW. These findings obtained above are useful information to develop the vitrification processes for disposal of HLLW.

DOI： 10.1063/1.5025778

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.surfcoat.2018.02.026

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Angewandte Chemie - International Edition  

Carbon nitride nanosheets (NS-C3N4) were found to undergo robust binding with a binuclear ruthenium(II) complex (RuRu′) even in basic aqueous solution. A hybrid material consisting of NS-C3N4 (further modified with nanoparticulate Ag) and RuRu′ promoted the photocatalytic reduction of CO2 to formate in aqueous media, in conjunction with high selectivity (approximately 98 %) and a good turnover number (>2000 with respect to the loaded Ru complex). These represent the highest values yet reported for a powder-based photocatalytic system during CO2 reduction under visible light in an aqueous environment. We also assessed the desorption of RuRu′ from the Ag/C3N4 surface, a factor that can contribute to a loss of activity. It was determined that desorption is not induced by salt additives, pH changes, or photoirradiation, which partly explains the high photocatalytic performance of this material.

DOI： 10.1002/anie.201701627

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その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/anie.201701627

掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

In this study, plasma irradiations to titanium were conducted to enhance the photocatalytic activity of titanium oxide. When titanium is exposed to He plasmas, various morphology changes occur as forming nano-bubbles near the surface. Photocatalytic activity of the oxidized helium plasma irradiated titanium samples with nano-cones and microstructures were assessed by the hydrogen production from aqueous methanol solution. It is shown that the He plasma irradiation increases the photocatalytic activity more than double. Moreover, nitrogen mixture plasma irradiation to titanium (oxide) was conducted for doping nitrogen, which has been regarded as method to create visible light reactivity. It is shown from X-ray photoelectron spectroscopy (XPS) analysis that nitrogen doping has been successfully conducted under specific conditions.

DOI： 10.7567/JJAP.55.106202

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その他リンク： http://stacks.iop.org/1347-4065/55/i=10/a=106202?key=crossref.69ed7b7971d62ec6f8c9129ecd2a2c59

記述言語：英語   出版者・発行元：Scientific Reports  

In this study, we show from helium (He) plasma irradiation to tantalum and iron surfaces that morphology changes in nanoscale occur on the both metals. In particular, from systematic irradiation experiments, it is identified that fuzzy nanostructures are grown on the both metals. The necessary conditions for the morphology changes are discussed based on the experimental results in terms of the helium migration, the physical sputtering, and the shear modulus of materials. Because oxides or oxinitrides of iron and tantalum are thought of as visible light responsive photocatalytic materials, the present work shows wide potential of usage of plasmas as a tool to tailor photocatalytic materials.

DOI： 10.1038/srep30380

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PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1088/1742-6596/712/1/012074

担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

DOI： 10.1088/1742-6596/712/1/012056

その他リンク： http://stacks.iop.org/1742-6596/712/i=1/a=012056?key=crossref.49278627889fb72fe760993783b12a62

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

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

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CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

We investigated the photocatalysis of dendritic nanostructured WO3/W composite materials fabricated by He plasma irradiation to tungsten plates, followed by the surface oxidation. The samples promoted the decolorization reaction of methylene blue (MB) aqueous solution under near infrared (NIR) light irradiation. To verify the MB molecule is actually decomposed by the photocatalysis of the samples, reaction products were analyzed by S K-edge XANES measurements for the MB solution kept with the samples under the light irradiation or in the dark. By the light irradiation, the σ∗(S-C) peak in the XANES spectra reduced and a new peak originated from SO42- species was clearly observed, suggesting that S-C bonds in a MB molecule are broken by the NIR light irradiation and finally the sulfur species exists in the solution in the state of SO42- ion. After the adsorption reaction in the dark, the XANES spectra of the sample surfaces showed a sharp π∗(S-C) peaks, indicating that MB molecules are adsorbed on the sample surfaces and stacked each other by the π-π interaction. These results demonstrate that the photocatalytic decomposition of MB molecules really proceeds over WO3/W composite materials even under NIR light irradiation.

DOI： 10.1016/j.nimb.2015.07.035

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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   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

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

Helium plasma irradiation to tungsten leads to formation of helium clusters, helium bubbles, and fiberform nanostructures near the surface. In this study, tungsten samples exposed to helium plasmas are analyzed by X-ray photoelectron spectroscopy in detail. The W 4f spectra and valence band spectra show chemical composition and electronic state of the surface. It was found that significant differences were not identified on the electronic state between the helium plasma irradiated and pristine samples when the degree of oxidization was the same level. From a low kinetic energy cut-off of X-ray photoelectron spectrum, the work function of the samples was measured. It was found that helium plasma irradiation increased the work function by approximately 0.5 eV when WO3/W was higher than unity. The possible mechanism to arise the difference in the work function is discussed.

DOI： 10.7567/JJAP.54.126201

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その他リンク： http://stacks.iop.org/1347-4065/54/i=12/a=126201?key=crossref.8de312670aa262f2ebe1e2556b349c69

掲載種別：研究論文（学術雑誌）   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

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Applied Physics  

It was found that the visible-light responsiveness of a nitrogen ion-implanted TiO2 photocatalyst was attributable to the predominant chemical states of nitrogen, depending on the local nitrogen concentration near the surface. In the present study, we examined the effects of conceivable nitrogen-related defects on the visible light responsiveness, based on electronic structures calculated from first principles. Possible chemical states were proposed by comparing previously reported experiments with the present theoretical N-K X-ray absorption spectra. The theoretically predicted visible light absorption spectra and carrier trap states due to the bandgap states associated with the defects well explained the relationship between the catalytic reactivity and the proposed chemical states.

DOI： 10.1063/1.4930811

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掲載種別：研究論文（学術雑誌）   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

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掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Hydrogen Energy  

The hydrogen storage property of the binary nanoparticles composed of Mg and Pd has been investigated by the QCM technique without the exposure to the air. The two types of nanoparticles have been fabricated by the gas evaporation method with the He gas. The one is the nanoparticles composed of the both Mg and Pd atoms (Mg-Pd NPs) and the other one is the composite of the Mg and Pd nanoparticles (Mg NPs-Pd NPs). Both the Mg-Pd NPs and the Mg NPs-Pd NPs can absorb the hydrogen under the room temperature and 1 atm of H2 gas. However, the desorptions of the hydrogen have not been observed about the both samples. We have also studied the chemical state of the NPs by XPS and XAFS. The XAFS analyses have revealed that the MgH2 in the NPs can not be dehydrogenated at the room temperature even if the catalytic effect of the Pd.

DOI： 10.1016/j.ijhydene.2015.04.087

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担当区分：責任著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

Ag loaded Ga2O3 (Ag/Ga2O3) photocatalysts for the reduction of CO2 with water have been prepared by impregnation (IMP) and two types of solution plasma methods (SPM1 and SPM2). Using X-ray absorption near edge structure (XANES) and Fourier transform infrared (FT-IR) spectroscopies, we have investigated the local electronic structures of Ag/Ga2O3 photocatalysts as well as the adsorption behaviors of CO2 during the reaction. Both Ag L3-edge and O K-edge XANES analyses reveal the Ag-Ga2O3 interaction, i.e., the charge-transfer from O atoms to Ag atoms, by demonstrating the decrease in the unoccupied Ag 4d-state density and increase in the unoccupied O 2p-state density. The strength of the interaction depends on the preparation method, and increases in the order of Ag/Ga2O3 (SPM2), Ag/Ga2O3 (SPM1) and Ag/Ga2O3 (IMP). In addition, FT-IR measurements have disclosed that Ag/Ga2O3 (IMP) obtains a larger amount of strongly basic sites as a result of the strongest interaction between Ag and Ga2O3. Although the amount of the adsorbed CO2 is different in each Ag/Ga2O3 sample, in the following formation process of bidentate formate species, no remarkable difference is detected among all samples. The bidentate formate species are likely to interact with H2O molecules to produce CO under photoirradiation, and this process would be affected by the strength of the Ag-Ga2O3 interaction, because this reaction hardly proceeds over Ag/Ga2O3 (SPM2) having the weakest Ag-Ga2O3 interaction.

DOI： 10.1016/j.nimb.2015.07.031

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担当区分：筆頭著者   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 Colloid and Interface Science  

The thickness-controlled TiO2 thin films are fabricated by the pulsed laser deposition (PLD) method. These samples function as photocatalysts under UV light irradiation and the reaction rate depends on the TiO2 thickness, i.e., with an increase of thickness, it increases to the maximum, followed by decreasing to be constant. Such variation of the reaction rate is fundamentally explained by the competitive production and annihilation processes of photogenerated electrons and holes in TiO2 films, and the optimum TiO2 thickness is estimated to be ca. 10nm. We also tried to dope nitrogen into the effective depth region (ca. 10nm) of TiO2 by an ion implantation technique. The nitrogen doped TiO2 enhanced photocatalytic activity 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 active sample, the additional electronic states were observed just above the valence band edge of a TiO2. The electronic state would be originated from the substituting nitrogen and be responsible for the band gap narrowing, i.e., visible light response of TiO2 photocatalysts.

DOI： 10.1016/j.jcis.2014.12.097

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PubMed

掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP Publishing  

DOI： 10.1088/1757-899x/76/1/012001

その他リンク： http://stacks.iop.org/1757-899X/76/i=1/a=012001?key=crossref.7841256626afcf78ba29911c124eb567

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

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

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CiNii Research

CiNii Research

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Materials Chemistry A  

Ag loaded Ga2O3 (Ag/Ga2O3) photocatalysts were prepared by an impregnation method and examined for the photocatalytic reduction of CO2 with water where CO, H2 and O2 were formed as products. TEM and X-ray absorption near edge structure (XANES) measurements revealed that around 1 nm sized Ag clusters were formed predominantly in an active Ag/Ga2O3 sample while partially oxidized large Ag particles with the size of several-several tens of nm were observed in a less active Ag/Ga2O3 sample. Both Ag L3-edge and O K-edge XANES analyses suggested that the small Ag clusters accepted more electrons in the d-orbitals as a result of the strong interaction with the Ga2O3 surface. In situ FT-IR measurements of the Ag/Ga2O3 samples showed CO3 stretching vibration bands assignable to monodentate bicarbonate and bidentate carbonate species chemisorbed on the Ga2O3 surface, and to monodentate carbonate species on the large Ag particles. Among these chemisorbed species, the monodentate bicarbonate and/or the bidentate carbonate species changed to bidentate formate species, as the reaction intermediate, under UV light irradiation. The bidentate formate species was formed not by the plasmonic excitation of the Ag nanoparticles but by the photoexcitation of the Ga2O3 semiconductor, and the formation process would be promoted at the perimeter of the Ag clusters on the Ga2O3 surface by the effective separation of electron-hole pairs.

DOI： 10.1039/c5ta04815j

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

Nitrogen was doped into TiO2 by an ion implantation technique to investigate the depth distribution of nitrogen most effective for fabricating a visible-light responsive photocatalyst. In the nitrogen-doped TiO2 samples, the photocatalytic activity under visiblelight irradiation was enhanced, wherein two types of chemical state of nitrogen, one photocatalytically active and the other inactive, were found depending on the nitrogen concentration, using electron energy loss spectroscopy. The depth distributions of nitrogen were quantified, so that the implanted nitrogen increased with thickness from the surface up to 90 nm, consistent with Monte Carlo simulations. The critical nitrogen concentration for the photocatalytically active species to form was estimated to be no higher than 1.8 atom%.We also derived semi-empirical equations fromthe present results to estimate the critical depth of nitrogen distribution effectively reactive to be 13 ± 5 nm from the surface.

DOI： 10.1002/sia.5542

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

The gold nanoparticles on titania support (AuNP/TiO2) has been paid attention as a catalyst and a photocatalyst. We perform the preparation of AuNP/TiO2, which is the combination of the sol-gel method and solution plasma method. In this method, we generate the plasma in the gelatinous peroxotitanic acid solution by the discharge between the gold electrodes, and then we synthesize the peroxotitanium gel containing gold nanoparticles. After drying and calcination process, we obtain the AuNP/TiO2 samples. The X-ray diffraction results show that the AuNP/TiO2 is constituted by the nanocrystalline gold and anatase-phase TiO2, and the lattice constant decreases by the embedded gold nanoparticles in the TiO2 matrix. Ultraviolet-Visible absorption spectroscopy shows that the AuNP/TiO2 samples absorb the visible light at about 630nm based on the localized surface plasmon resonance of gold nanoparticles embedded in the TiO2 matrix. The surface chemical states of the AuNP/TiO2 samples are analyzed by the X-ray photoelectron spectroscopy. The surface of AuNP/TiO2 is composed with the majority of oxidized gold and minority of metallic gold which interacted with the TiO2 surface. The Au L3-edge near edge X-ray absorption fine structure spectra indicate that the gold nanoparticles embedded in TiO2 have metallic chemical states. We successfully prepare the gold nanoparticles on the surface and in the matrix of anatase-phase TiO2.

DOI： 10.1002/sia.5567

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掲載種別：研究論文（学術雑誌）   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

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Surface and Interface Analysis  

The nanoparticles composed of Mg and Pd atoms (Mg-Pd NPs) have been fabricated by the gas evaporation method, and the variation of the chemical state during hydro-/dehydrogenations has been investigated by X-ray photoelectron spectroscopy (XPS) and in-situ X-ray absorption fine structure (XAFS) analyses. Both XPS and XAFS spectra have indicated that the Mg-Pd NPs contain the chemical state of the metallic Pd and Mg-Pd alloy phases. The Mg-Pd alloy phase has been identified as MgPd and Mg6Pd by the Pd K-edge EXAFS analysis. The hydrogen release of the Mg-Pd NPs has not been observed after first hydrogenation due to the migration of Mg toward the surface of the Mg-Pd NPs during the hydrogen storage. This irreversible migration has led the inhibition of the hydrogen diffusion into the surface from the inside of the Mg-Pd NPs.

DOI： 10.1002/sia.5647

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Japanese Journal of Applied Physics  

The absorption spectra of the HCl, NaCl, and NaOH solutions during and after the solution plasma sputtering for the preparation of gold nanoparticles are measured by in situ ultraviolet-visible (UV-vis) spectroscopy to determine the particle diameter and behavior. In the solution plasma sputtering, gold particles are directly formed from the plasma phase and not by the reduction of Au3+ ions dissolved from electrodes. The initial diameter and behavior differ according to the solution used. In HCl solution, gold nanoparticles are formed and dissolve into Au3+ ions. When the solution is saturated, the gold nanoparticles grow by the aggregation of Au3+ ions. Cluster-sized particles are formed in NaCl solution that constitute nanoparticles, which are very stable for several days. Gold nanoparticles of 3 nm diameter are formed in NaOH solution, which aggregate over several days. The contribution of chlorine ions to the day-order stability of gold nanoparticles is suggested.

DOI： 10.7567/JJAP.53.11RA03

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その他リンク： http://stacks.iop.org/1347-4065/53/i=11S/a=11RA03?key=crossref.abf0db48a09f1feadf9e0e6809c9acc1

掲載種別：研究論文（学術雑誌）   出版者・発行元：Applied Surface Science  

Helium plasma irradiation to metals could be a potential novel surface modification method in nanoscale. In this study, systematic helium plasma irradiations to titanium were conducted in low ion energy (<100 eV) and high fluence (>10 25 m -2 ) regime. From the surface analysis by scanning electron microscopy and transmission electron microscopy, various types of morphology changes, i.e. nanocone, pinhole, porous structure, and rough surfaces, were identified. The experimental conditions that control the various morphology changes are revealed from the aspect of the incident ion energy and the surface temperature. Based on the observations, it is thought that helium bubble growth, surface diffusion, and physical sputtering played important roles for the morphology change. © 2014 Elsevier B.V.

DOI： 10.1016/j.apsusc.2014.03.022

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.69.1.2.0_270_1

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

The dendritic nanostructure was fabricated on a surface of tungsten plate by helium plasma irradiation. The nanostructure consisting of W metal was partially oxidized to form WO3 on exposure to air, and the resulting surface exhibited a broad photoabsorption in the range from 1 to 5 eV. We examined photoinduced reaction of methylene blue (MB) on the material. It was found that the partially and fully oxidized surface nanostructures were able to promote a decolorization of MB under photoirradiation even with the near-infrared light (< 1:55 eV), whose energy is lower than the band gap of WO3. The reaction rate was varied with the fraction of W and WO 3 on the surface layers, that is, the partially oxidized sample promoted the reaction at a higher rate than the fully oxidized one. It is also found that the reaction rate decreased with time, which would be caused by the products accumulation on the surface and the surface oxidation. © 2014 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2014.343

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CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：The Surface Analysis Society of Japan  

<p>  The PC liposomes constructed with one lipid bilayer have been fabricated without using chloroform solution and phosphate-buffer saline. After reaction promotion, the Au NPs covered with PC molecules exist on the outside of the liposome membrane. The thickness of the liposome membrane is estimated to be approximately 5 nm.</p>

DOI： 10.1384/jsa.20.230

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

Ag loaded Ga2O3 (Ag/Ga2O3) has exhibited photocatalytic activity for CO2 reduction with water to produce COas well as for water splitting to H2 and O2. In-situ FT-IR measurements have shown CO3 stretching vibration bandsassignable to carbonate and bicarbonate species when CO2 molecules chemisorbed on the catalyst surface. Thesespecies change to bidentate formate species under photoirradiation. It subsequently converts to CO by interactingwith water molecules, not chemisorbed OH on the catalyst surface. This result suggests that formate species isan intermediate of the photocatalytic CO2 reduction. On the other hand, Au loaded Ga2O3 (Au/Ga2O3) hasproduced H2 predominantly with a very small amount of CO formation, since the less amount of CO2 moleculeschemisorb on Au/Ga2O3. FT-IR measurements of the Ag/Ga2O3 with high Ag loading have shown carbonatespecies due to the adsorption of atmospheric CO2 on hydroxyl group. The carbonate species is too unstable underphotoirradiation to convert into formate species, but is stabilized as CO2-3 species by the reaction with water.XANES analysis has revealed that atomically dispersed Ag metal species may be effective for the adsorption ofCO2 and the subsequent conversion into formate species to promote the photocatalytic CO2 reduction. © 2014 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2014.299

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CiNii Research

出版者・発行元：20th World Hydrogen Energy Conference, WHEC 2014  

The hydrogen storage property of the nanoparticles composed of the Mg and Pd atoms (Mg-Pd NPs) has been investigated by QCM technique without the exposure to the air. We have also studied the chemical state of the Mg-Pd NPs by XPS and XAFS. The Mg-Pd NPs can store the hydrogen under the room temperature and 1 atm of H2 gas. However, the release of the hydrogen has not been observed. XAFS study has revealed that the irreversible change of the Mg-Pd NPs has caused the inhibition of the release of hydrogen.

Scopus

出版者・発行元：20th World Hydrogen Energy Conference, WHEC 2014  

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 the 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. The XPS results show that the Mg and the Ni nanoparticles as prepared sample possess almost clean surface. However, this materials has not been hydrogenated under hydrogen atmospheric pressure at 303 K. The QCM results indicate that the hydrogen storage ability of this materials has been lost by the adsorption of residual gases even under vacuum condition in several hours after the end of fabrication. The XPS results after hydrogen exposure show that 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.

Scopus

出版者・発行元：20th World Hydrogen Energy Conference, WHEC 2014  

The hydrogen storage property of the binary nanoparticles composed of Mg and Pd has been investigated by QCM technique without the exposure to the air. The two types of nanoparticles have been fabricated by the gas evaporation method with He gas. The one is the nanoparticles composed of the both Mg and Pd atoms (Mg-Pd NPs) and the other one is the composite of the each Mg and Pd nanoparticles (Mg NPs-Pd NPs). We have also studied the chemical state of the nanoparticles by XPS and XAFS. Both the Mg-Pd NPs and the Mg NPs-Pd NPs can store the hydrogen under the room temperature and 1 atm of H2 gas. However, the releases of the hydrogen have not been observed about the both samples. XAFS study has revealed that the irreversible change of the Mg-Pd NPs has caused the inhibition of the release of hydrogen. On the other hand, it seems that the Mg NPs-Pd NPs cannot release the hydrogen due to the stability of the MgH2 or the low hydrogen diffusion property inside of the MgH2.

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：公益社団法人 日本表面真空学会  

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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CiNii Research

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 Applied Physics  

It has been found recently that low-energy helium (He) plasma irradiation to tungsten (W) leads to the growth of W nanostructures on the surface. The process to grow the nanostructure is identified as a self-growth process of He bubbles and has a potential to open up a new plasma processing method. Here, we show that the metallic nanostructure formation process by the exposure to He plasma can occur in various metals such as, titanium, nickel, iron, and so on. When the irradiation conditions alter, the metallic cone arrays including nanobubbles inside are formed on the surface. Different from W cases, other processes than growth of fiberform structure, i.e., physical sputtering and the growth of large He bubbles, can be dominant on other metals during irradiation; various surface morphology changes can occur. The nanostructured W, part of which was oxidized, has revealed a significant photocatalytic activity under visible light (wavelength >700 nm) in decolorization of methylene blue without any co-catalyst. © 2013 American Institute of Physics.

DOI： 10.1063/1.4798597

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

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 Catalysis  

Photocatalytic steam reforming of methane (PSRM; 2 H 2O (g) + CH 4 → 4 H 2 + CO 2) was examined over metal-loaded K 2Ti 6O 13 photocatalysts. Although the production rate was improved by loading Pt cocatalyst on the K 2Ti 6O 13 photocatalyst, unfavorable formation of CO and gradual deactivation of photocatalyst were observed. On the other hand, a Rh-loaded K 2Ti 6O 13 sample showed two times higher activity than the Pt-loaded one did, and promoted the PSRM selectively without deactivation for many hours. In the highly active Rh-loaded photocatalyst, the Rh cocatalyst existed as a mixture of small metallic rhodium and large rhodium oxide particles. The photocatalytic activity tests for hydrogen evolution and oxygen evolution from each aqueous solution of sacrificial reagent (methanol and silver nitrate, respectively) revealed that the metallic rhodium particles and the rhodium oxide particles could function as cocatalysts preferably for reduction and oxidation, respectively. Also on a Na 2Ti 6O 13 photocatalyst, a mixture of rhodium metal and oxide similarly enhanced the photocatalytic activity. Thus, it is suggested that the Rh cocatalyst on these alkaline titanates bifunctionally promoted the PSRM. © 2012 American Chemical Society.

DOI： 10.1021/cs2006229

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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 Catalysis B: Environmental  

Photocatalytic hydrogen production from aqueous ethanol was investigated over Au-loaded titanium oxide under visible light (510-740. nm) irradiation. Hydrogen was constantly produced through the present plasmonic photocatalysis. In this system, Au nanoparticles with larger particle size were essentially effective for the reaction due to the high efficiency for the localized surface plasmon resonance (LSPR). Further, Au nanoparticles with short rod-like shapes were more effective for the reaction than those with spherical shape because of the higher efficiency for the electron transfer from the Au nanoparticle to the conduction band of titanium oxide. On the other hand, aggregates of the Au nanoparticles were not appropriate for the reaction, which derived from the low efficiency of the electron transfer. Finally, titanium oxide containing anatase phase with larger particle size was most preferred for the reaction. © 2011 Elsevier B.V..

DOI： 10.1016/j.apcatb.2011.12.029

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者  

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Web of Science

出版者・発行元：NANOCON 2012 - Conference Proceedings, 4th International Conference  

The chemical state around the Mg and Pd atoms in the Mg-Pd nanoparticles has been investigated by the Mg K- and Pd L3-edges NEXAFS techniques under in-situ condition. The Mg-Pd nanoparticles possess metallic Mg and Pd states and the surface of the Mg-Pd nanoparticles is partly oxidized. Moreover, both the Mg K- and Pd L3-edges NEXAFS spectra show that the Mg-Pd alloy phases are formed in the Mg-Pd nanoparticles. The variation of the chemical states around the Pd atom after the cycles of the exposure to the H2 gas has been also investigated by the Pd L3-edge NEXAFS technique. The Mg-Pd alloy phases dissociate by the cycles of hydrogenation and dehydrogenation.

Scopus

出版者・発行元：NANOCON 2012 - Conference Proceedings, 4th International Conference  

We have revealed the radiation damage for the cys/Au NPs/Ni sample by the X-ray irradiation at the energy regions of N and O K-edges NEXAFS. The Au NPs colloidal solution is fabricated by the solution plasma method, and the adsorption reaction between the Au NPs and L-cysteine is promoted under water environment. About the cys/Au NPs/Ni sample after the X-ray irradiation, the radiation damages appear at N and O K-edges NEXAFS, S2p XPS and N1s XPS spectra. It is found that the L-cysteine adsorbates desorb from the Au NPs surface. This desorption occurs by means of the electron bombardment of secondary electrons excited from the Au NPs surface.

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

It was found that nitrogen-doped TiO2 revealed significant improvement in high photocatalytic reactivity under visible-light [Asahi et al, Science 293, 269-271 (2001).] To investigate the optimal local concentration of doped nitrogen for visible-light response, N+-implanted TiO2 samples were examined by means of X-ray absorption near edge structure (XANES) and electron energy loss spectroscopy (EELS). Depth-resolved N K-edge in EELS revealed two types of chemical state of nitrogen, depending on the concentration, which was consistent with the XANES results. We found that the local nitrogen concentration effective for visible-light response was less than &#61566;1 at%. Further, we visualized the spatial distributions of the different chemical states of nitrogen by energy-filtering TEM (EFTEM). It was also found that the photocatalytic active state was offset by the coexisting photocatalytic inactive state.

担当区分：筆頭著者  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

Direct evidences of hydrogen loosely trapped between graphene layers in nanostructured graphite prepared by mechanical milling in a hydrogen atmosphere are presented, based on a combinational study of FT-IR, electron diffraction (ED) and electron energy-loss spectroscopy (EELS). The FT-IR spectrum of nanostructured graphite exhibited a new broad absorption band at very low frequencies around 660 cm-1, which almost disappeared by annealing up to 800 K. ED and plasmon peaks in EELS detected the unusual shrinkage and subsequent expansion of the fragmented graphene interlayer distance by hydrogen incorporation and desorption with annealing, well correlated with the change in intensity of the 660 cm-1 IR band. All the present results support our previous studies

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Energetic nitrogen ion was injected into a TiO2 photocatalyst in order to investigate the optimal local concentration of doped nitrogen for visible-light response. N+-implanted TiO2 samples promoted the photocatalytic activity under visible-light irradiation. N K-edge XANES of the highest activity sample indicated that N replaces the O sites near the surface, whereas in the samples of higher N+ fluence, N-O and/or N-N species formed. Depth-resolved N K-edge ELNES revealed the two types of N, depending on the concentration, and we found the local N concentration effective for visible-light response was less than ~1 at%. Further, the spatial distributions of the different chemical states of N by energy-filtering TEM (FETEM) supported these findings.

記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

In order to examine x-ray absorption near-edge structures (XANES) of disordered solid solutions of metal oxides, a combined approach of a first principles sipercell method and a cluster expansion method is developed. Zn-L3 edge XANES are measured on a series of Mg1-xZnxO with a rocksalt structure in the range of x = 0.025-0.3 using synchrotron source. A first principles orthogonalized linear combinations of an atomic orbital method is employed to obtain a theoretical spectrum of a given model. A Zn-2p core hole is included in the calculation, and a set of 128 atom supercells is used. Theoretical XANES of disordered solid solutions are obtained as a weighted sum of theoretical spectra for four ordered structures, with the weighting factors determined by the cluster expansion method. The dependence of the spectral shape on the solute concentration is reproduced only when the averaged environment of solute atoms as determined by the solute concentration solution is confirmed by the Monte Carlo calculations.

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

We propose novel methods of depth-resolved EELS (DREELS) and chemical state mapping, and the techniques were applied to the cross-sectional TEM (XTEM) sample of N+ implanted TiO2 catalyst. The methods successfully extracted the depth dependence of the N-K ELNES and the spatial distributions of the constituent chemical states separately.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：日本語  

記述言語：日本語  

担当区分：筆頭著者   記述言語：日本語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

A technique has been proposed to increase the efficiency of hydrogen production from water by γ-ray radiolysis as an effective use of radioactive waste. This is possible by putting special metal structures into water to enhance the conversion of MeV range γ-ray to low-energy electrons which escape from metal into water. The experimental results showed that hydrogen production could be significantly enhanced by carefully controlling the thickness of metal components and the proximity with adjacent metal components.

担当区分：筆頭著者   記述言語：日本語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

This is a proposal attempting to convert g-ray energy into electric energy via differentiated secondary electron generation by g-ray interacting with two different metal components. In this preliminary study, the maximum generated electric current and power were respectively 0.58 mA and 0.093 mW.

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

X-ray absorption technique was applied to analyze the local structures of fused and synthesized silica glasses before and after the irradiation in a nuclear reactor. Si K-edge EXAFS revealed changes in the SiO4 tetrahedron structure by the irradiation, i.e. a distorted tetrahedron in the silica glass returned to more regular one but the connection between neighboring tetrahedrons became looser.

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have proposed a technique to enhance the decomposition of carbon dioxide by gamma-ray irradiation. This is possible by putting metal components into carbon dioxide CO2 gas to promote the conversion of gamma-ray to lower-energy electrons through Compton, photoelectron, and cascading electron knock-on events in metals.

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：日本語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

DOI： 10.11316/jpsgaiyo.56.2.4.0_801_3

CiNii Research

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：日本語  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

記述言語：英語   掲載種別：研究論文（学術雑誌）  

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

総ページ数：x, 341p   記述言語：日本語

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