Hidenori Noguchi
National Institute for Materials Science
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Featured researches published by Hidenori Noguchi.
Physical Chemistry Chemical Physics | 2001
Shigeru Ikeda; Noboru Sugiyama; Bonamali Pal; Giuseppe Marci; Leonardo Palmisano; Hidenori Noguchi; Kohei Uosaki; Bunsho Ohtani
Photocatalytic reactions by transition-metal (V, Cr, Fe, Co, Cu, Mo, or W) loaded TiO2 (M-TiO2) powders suspended in aqueous solutions of methanol, (S)-lysine (Lys), or acetic acid were investigated. The photoactivities of various samples were compared with the rate constant (kr) of recombination of photoexcited electrons and positive holes determined by femtosecond pump–probe diffuse reflection spectroscopy (PP-DRS). As a general trend, increased loading decreased the rate of formation of the main products (H2 , pipecolinic acid (PCA), and CO2) under UV (>300 nm) irradiation, and the effect became more intense on increasing the loading. In PP-DRS, these M-TiO2 gave similar decays of absorption at 620 nm arising from excitation by a 310 nm pulse (<100 fs). The second-order rate constant (kr) markedly increased with loading, even at a low level (0.3%) and further increased with an increase in loading up to 5%. The photocatalytic activity of platinized M-TiO2 for H2 and PCA production under deaerated conditions depended strongly on kr, but the relation between kr and the rate of CO2 production by unplatinized M-TiO2 under aerated conditions was ambiguous; other factor(s) might control the rate of the latter. These different kr dependences of photoactivity on the reaction kinetics governed by e−–h+ recombination were attributed to the presence of O2 and Pt deposits. A simple kinetic model to explain the overall rate of these photocatalytic reactions is proposed, and the effect of recombination kinetics on photoactivity is discussed.
Physical Chemistry Chemical Physics | 2003
Shigeru Ikeda; Noboru Sugiyama; Shin-ya Murakami; Hiroshi Kominami; Yoshiya Kera; Hidenori Noguchi; Kohei Uosaki; Tsukasa Torimoto; Bunsho Ohtani
The molar amounts of defective sites (Md) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. Measurements of pH dependence of typical anatase and rutile TiO2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO2 in ranges of 0–0.35 V for anatase and 0–0.25 V for rutile. A linear relation of Md with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that Md could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between Md and the specific surface area suggests that the surface area was not directly reflected on Md. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and Md revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.
Journal of the American Chemical Society | 2014
Kohei Uosaki; Ganesan Elumalai; Hidenori Noguchi; Takuya Masuda; Andrey Lyalin; Akira Nakayama; Tetsuya Taketsugu
Boron nitride (BN), which is an insulator with a wide band gap, supported on Au is theoretically suggested and experimentally proved to act as an electrocatalyst for oxygen reduction reaction (ORR). Density-functional theory calculations show that the band gap of a free h-BN monolayer is 4.6 eV but a slight protrusion of the unoccupied BN states toward the Fermi level is observed if BN is supported on Au(111) due to the BN-Au interaction. A theoretically predicted metastable configuration of O2 on h-BN/Au(111), which can serve as precursors for ORR, and free energy diagrams for ORR on h-BN/Au(111) via two- and four-electron pathways show that ORR to H2O2 is possible at this electrode. It is experimentally proved that overpotential for ORR at the gold electrode is significantly reduced by depositing BN nanosheets. No such effect is observed at the glassy carbon electrode, demonstrating the importance of BN-substrate interaction for h-BN to act as the ORR electrocatalyst. A possible role of the edge of the BN islands for ORR is also discussed.
Polymer Chemistry | 2010
Yohei Tateishi; Naoki Kai; Hidenori Noguchi; Kohei Uosaki; Toshihiko Nagamura; Keiji Tanaka
The local conformation of poly(methyl methacrylate) (PMMA) chains at the nitrogen (N2) and water interfaces was studied by infrared-visible sum-frequency generation (SFG) spectroscopy. Although SFG spectra in the C–H region for PMMA at the N2 interface have been hitherto reported, the peak assignments are not in accord with one another. Thus, we first made accurate assignments of SFG peaks using films, which had been well annealed at a temperature above the glass transition temperature for a long time, of three different deuterated PMMAs as well as normal protonated PMMA. At the N2 interface, hydrophobic functional groups such as α methyl, ester methyl and methylene groups were present. While the α methyl group was oriented along the direction parallel to the interface, ester methyl and methylene groups were oriented normal to the interface. Quantitative discussion concerning the orientation of the functional groups of PMMA at the N2 interface was aided by a model calculation. Once the PMMA film contacted water, the carbonyl groups of the PMMA side chains were oriented to the water phase to form hydrogen bonds with water molecules, resulting in the migration of ester methyl into the internal region of the film. Concurrently, the methylene groups became randomly oriented at the water interface and/or in part migrated into the internal region. Interestingly, the α methyl groups still existed at the water interface oriented along the parallel direction. The outermost region of PMMA in water can consist of hydrophilic and hydrophobic domains with sub-nanometre scale. Water molecules H-bond to themselves near the hydrophobic domains, leading to the formation of an ice-like structure of water molecules. However, water molecules adjacent to the hydrophilic domains H-bond with carbonyl groups.
Applied Physics Letters | 2013
Takuya Masuda; Hideki Yoshikawa; Hidenori Noguchi; Tadahiro Kawasaki; Masaaki Kobata; Keisuke Kobayashi; Kohei Uosaki
In situ electrochemical X-ray photoelectron spectroscopy (XPS) apparatus, which allows XPS at solid/liquid interfaces under potential control, was constructed utilizing a microcell with an ultra-thin Si membrane, which separates vacuum and a solution. Hard X-rays from a synchrotron source penetrate into the Si membrane surface exposed to the solution. Electrons emitted at the Si/solution interface can pass through the membrane and be analyzed by an analyzer placed in vacuum. Its operation was demonstrated for potential-induced Si oxide growth in water. Effect of potential and time on the thickness of Si and Si oxide layers was quantitatively determined at sub-nanometer resolution.
Research on Chemical Intermediates | 2007
Shin-ya Murakami; Hiroshi Kominami; Yoshiya Kera; Shigeru Ikeda; Hidenori Noguchi; Kohei Uosaki; Bunsho Ohtani
Electron-hole recombination in nano-sized titanium(IV) oxide (TiO2) particles with various physical properties, which have been shown to be highly active photocatalysts, was evaluated by quantitative analysis of reduced titanium species (Ti3+), which might be formed at crystalline defective sites in TiO2 particles through photo-irradiation in the presence of a hole scavenger under deaerated conditions. These highly active photocatalyst samples were synthesized by hydrothermal crystallization in organic media (HyCOM method) and post-calcination. The Ti3+ density decreased with increasing calcination temperature (Tc), and a linear correlation was observed between the Ti3+ density and rate constant for electron-hole recombination evaluated by femtosecond pump-probe diffuse reflection spectroscopy. Reaction rate (RAg) and the amount of silver ions (Ag+) adsorbed on TiO2 particles ([Ag+]ads) were measured for photocatalytic silver metal deposition along with oxygen formation from an aqueous Ag+ solution under deaerated conditions, and the slope of the RAgversus [Ag+]ads plot was determined. Kinetic investigation of this reaction showed that the reciprocal of the slope was approximately related to the ratio of the rates for electron-hole recombination and electron trapping (kr/ke ratio). The kr/ke ratio decreased as Tc increased, and the logarithm of the kr/ke ratio was linearly related with Ti3+ density. These two parameters were used as a measure for the recombination properties of TiO2 photocatalysts with various physical properties.
Journal of the American Chemical Society | 2008
Hidehiko Asanuma; Hidenori Noguchi; Kohei Uosaki; Hua-Zhong Yu
Nucleic acids possess charged phosphate groups in their backbones, which require counterions to reduce the repulsive Coulombic interactions between the strands. Herein we report how different mono- and divalent metal cations influence the molecular orientations of DNA molecules on silicon surfaces upon immobilization and hybridization. Our sum frequency generation (SFG) spectroscopy studies demonstrated that the degree of conformational variation of DNA self-assembled monolayers on silicon depends on the type of metal cations present. The molecular orientation change of immobilized single-stranded oligonucleotides correlates with DNA-cation affinity (Mg(2+) > Ca(2+) > K(+) approximately Na(+)): metal cations with the strongest affinity disrupt the structure of the underlying linker monolayer the most. Upon hybridization the trend is reversed, which is attributed to the greater ability of divalent cations to mask the negative charges on the DNA backbone. These findings provide useful information for the construction of more sensitive DNA biosensors, particularly the optimization of on-chip hybridization performance.
Colloids and Surfaces B: Biointerfaces | 2012
Takuya Kondo; Kouji Nomura; Masanobu Murou; Makoto Gemmei-Ide; Hiromi Kitano; Hidenori Noguchi; Kohei Uosaki; Kohji Ohno; Yoshiyuki Saruwatari
A zwitterionic poly(carboxymethylbetaine) (PCMB) brush was prepared on a fused quartz prism by the surface-initiated atom transfer radical polymerization (SI-ATRP) of CMB monomer. The conformation of PCMB brush and the state of water at the surface of the brush were examined using sum frequency generation (SFG) technique. The C-H stretching band of the brush, indicating the gauche defect of the brush, was affected by the contact medium such as dry nitrogen, water vapor-saturated nitrogen and liquid water. The water molecules at the PCMB-water interfaces were not largely oriented in comparison with the interfacial water of both bare and the ATRP-initiator-modified quartz prisms. The similar tendency was previously observed for water in the vicinity of water-soluble zwitterionic polymers and polymer thin films using Raman and attenuated total reflection (ATR) infrared spectroscopies, respectively. The electrical neutralization between neighboring positive and negative charges might diminish the electrostatic adsorption of water molecules to the vicinity of zwitterionic polymer brushes.
Journal of the American Chemical Society | 2010
Kohei Uosaki; Hidenori Noguchi; Rie Yamamoto; Satoshi Nihonyanagi
Interfacial structures of alkylated polyvinylpyridine (Cn-PVP) brushes with various side chain lengths (n = 2, 6, 12) in dry nitrogen, water vapor, liquid water, and aqueous electrolyte solution were investigated by sum frequency generation (SFG) spectroscopy. The SFG spectra of the polymer brushes in the CH stretching region in dry nitrogen revealed that the conformational order of the side chain depended on the chain length. The conformational order of the polymer brush with hexyl, C6, side chain, was very high, and the side chain was almost in all-trans conformation with the tilt angle of methyl group being ca. 34° with respect to the surface normal. Significant contribution from CH stretching of methylene group was observed in the SFG spectra of the polymer brush with the shorter, ethyl, C2, or longer, decyl, C12, side chains. Relative intensity of CH stretching of methylene group to that of methyl group, that is, degrees of gauche defects, increased significantly upon in contact with water vapor at all the brushes, and essentially no CH stretching peaks were observed when the brushes were in contact with liquid water, showing almost completely disordered conformational structure. These conformation changes were very fast, suggesting that the changes were related to the orientation change of the side chains. SFG spectra of the brush/water interface in the OH stretching region were dominated by OH stretching vibration of ice-like water. The higher was the electrolyte concentration, the lower was the OH intensity, reflecting the reduction of the double layer thickness in solution of higher electrolyte concentration.
Energy and Environmental Science | 2015
Rajesh Kodiyath; Gubbala V. Ramesh; Eva Koudelková; Toyokazu Tanabe; Mikio Ito; Maidhily Manikandan; Shigenori Ueda; Takeshi Fujita; Naoto Umezawa; Hidenori Noguchi; Katsuhiko Ariga; Hideki Abe
Novel intermetallic TaPt3 nanoparticles (NPs) are materialized, which exhibit much higher catalytic performance than state-of-the-art Pt3Sn NPs for electrooxidation of ethanol. In situ infrared-reflection-absorption spectroscopy (IRRAS) elucidates that the TaPt3 NPs cleave the C–C bond in ethanol at lower potentials than Pt NPs, efficiently promoting complete conversion of ethanol to CO2. Single-cell tests demonstrate the feasibility of the TaPt3 NPs as a practical energy-extraction catalyst for ethanol fuels, with more than two times higher output currents than Pt-based cells at high discharge currents.