Yoriko Matsuoka

Visible light-sensitive mesoporous N-doped Ta2O5 spheres: synthesis and photocatalytic activity for hydrogen evolution and CO2 reduction

Crystallized mesoporous tantalum pentoxide spheres (CMTS) with particle diameters of ca. 100–500 nm and composed of Ta2O5 nanocrystals were synthesized for the first time by a combination of the sol–gel process and heat-treatment with the aid of carbon reinforcement. The specific surface area of the CMTS was up to 105 m2 g−1 and the pore diameter was controllable in the range of 5.6–17 nm by changing the crystallization temperature. Visible light-sensitive p-type N-doped Ta2O5 (N-CMTS) containing 5 at% N was successfully obtained by treatment of CMTS with ammonia, while retaining the mesoporosity and morphology of CMTS. N-CMTS exhibited excellent photocatalytic activity for hydrogen evolution and CO2 reduction (with ruthenium-complex) under visible light irradiation (≥410 nm) due to their larger surface area and controlled morphology compared with previously reported N-doped Ta2O5 fine particles.

Nitrogen and transition-metal codoped titania nanotube arrays for visible-light-sensitive photoelectrochemical water oxidation.

Vertically aligned titanium dioxide nanotube (TNT) arrays codoped with nitrogen and 3d transition metals were successfully fabricated using anodization and nitridation processes. The codoping of N and Fe yielded the highest visible-light-induced photoelectrochemical water oxidation due to bandgap narrowing of impurity levels by N and Fe.

An ideal nanostructure of polymer/BaTiO3 dielectric materials with high reliability for breakdown strength: isolated and uniformly dispersed BaTiO3 nanoparticles by thick polymer shells

Poly(methyl methacrylate)s (PMMAs) with various chain lengths were grafted onto barium titanate (BT) particles using surface-initiated polymerization. The obtained core–shell particles were blended with additional PMMA to yield nanocomposites where the BT particles could not approach each other due to the PMMA shells (PMMA-BT). It was confirmed that the BT particles were uniformly dispersed in PMMA-BT by SEM observation. Reliability of the dielectric properties of PMMA-BT was evaluated under an alternating current electric field at 50 Hz using 16 specimens, and compared to that of conventional nanocomposites prepared by blending PMMA with the unmodified BT nanoparticles. The homogeneous distribution of the BT particles for PMMA-BT had no great influence on the reliability of complex relative permittivity while it improved the reliability for the dielectric breakdown strength EDB. The superior reliability for the EDB of PMMA-BT would result from the absence of percolation of the BT particles in the PMMA-BT system. This finding demonstrates that the nanostructure where the BT particles are isolated and uniformly dispersed by polymer shells is ideal for high EDB reliability.

Highly crystalline β-FeOOH(Cl) nanorod catalysts doped with transition metals for efficient water oxidation

The application of the water oxidation reaction to extract electrons from water molecules is important for the future sustainable synthesis of useful chemicals such as hydrogen and organic compounds. Therefore, a cost-effective oxygen evolution reaction (OER) in alkaline, neutral or acidic solution is required, based on the use of catalysts incorporating earth abundant elements. This work demonstrates that β-FeOOH(Cl) nanorod catalysts with high crystallinity and small size (an average diameter of 3 nm and a length of 15 nm) provided the best performance in the OER activity among Fe-based oxide and (oxy)hydroxide catalysts. The pristine β-FeOOH(Cl) nanorods with the high crystallinity are realized by a new process enabling one-pot, fast, and room temperature synthesis, which is the key to forming colloidal suspensions of the highly crystallized pure-phase β-FeOOH(Cl) nanorods. The versatility of this process also enabled doping of a wide variety of transition metals. Doping of Ni2+ (at 1.2 at%) improved the OER activity and shifted the threshold potential in the negative direction by 100 mV in an alkaline electrolyte, which was comparable to that of conventional IrOx colloidal nanoparticles.

SPONTANEOUS FORMATION OF MULTIPLE LAND-AND-GROOVE STRUCTURES OF SILICA THIN FILMS

We found spontaneous formation of microscopic multiple land-and-groove structures of silica thin films. Silica and nickel were simultaneously deposited onto glass substrates from two opposite oblique directions to form columnar structures of silica among which nickel nanoparticles were embedded. Then nickel was dissolved in hydrochloric acid solution. After the dissolution of the nickel particles the columns of silica became very unstable and coalesced to form the multiple land-and-groove structures. The grooves are oriented to the direction perpendicular to the two deposition directions. The distances between the neighboring grooves are fairly uniform, and can be controlled between several hundred nanometers and several microns by changing the film thickness and the ratio of the nickel deposition rate to the silica deposition rate. The process found here may propose a new class of micro fabrication techniques in contrast to the artificial photolithography.