Tsutomu Aida

Correlation between Chemical Dopants and Topological Defects in Catalytically Active Nanoporous Graphene.

The interplay between chemical dopants and topological defects plays a crucial role in electrocatalysis of doped graphene. By systematically tuning the curvatures, thereby the density of topological defects, of 3D nanoporous graphene, the intrinsic correlation of topological defects with chemical doping contents and dopant configurations is revealed, shining lights into the structural and chemical origins of HER activities of graphene.

Laser-Doppler vibrating tube densimeter for measurements at high temperatures and pressures

A laser-Doppler vibrometer was used to measure the vibration of a vibrating tube densimeter for measuring P-V-T data at high temperatures and pressures. The apparatus developed allowed the control of the residence time of the sample so that decomposition at high temperatures could be minimized. A function generator and piezoelectric crystal was used to excite the U-shaped tube in one of its normal modes of vibration. Densities of methanol-water mixtures are reported for at 673 K and 40 MPa with an uncertainty of 0.009 g/cm3.

Electric Properties of Dirac Fermions Captured into 3D Nanoporous Graphene Networks.

Nanoporous graphene- based electric-double-layer transistors (EDLTs) are successfully fabricated. Transport measurements of the EDLTs demonstrate that the ambipolar electronic states of massless Dirac fermions with a high carrier mobility are well preserved in 3D nanoporous graphene along with anomalous nonlinear Hall resistance and exceptional transistor on/off ratio. This study may open a new avenue for device applications of graphene.

Green solvent for green materials: a supercritical hydrothermal method and shape-controlled synthesis of Cr-doped CeO2 nanoparticles.

This paper describes a supercritical hydrothermal synthesis method as a green solvent process, along with products based on this method that can be used as green materials that contribute to solving environmental problems. The first part of this paper summarizes the basics of this method, including the mechanism of the reactions, specific features of the supercritical state for nanoparticle synthesis, the continuous flow-type reactor and applications; this provides a better understanding of the suitability of this method to synthesize green materials. The second part of the paper describes the method used to synthesize Cr-doped CeO2 nanoparticles, which show an extremely high oxygen storage capacity, suggesting their high potential as an environmental catalyst. Transmission electron microscopy and scanning electron microscope images showed octahedral Cr-doped CeO2 nanoparticles with sizes of 15–30 nm and cubic Cr-doped CeO2 nanoparticles with sizes of 5–8 nm. Octahedral Cr-doped CeO2 nanoparticles exposing (111) facets and cubic Cr-doped CeO2 nanoparticles exposing (100) facets were determined by high-resolution transmission electron microscopy and selected area electron diffraction. The X-ray diffraction peaks shifted to a high angle because the radius of the Cr ion is smaller than that of the Ce ion.

MD Simulation of the Self-diffusion Coefficient and Dielectric Properties of Expanded Liquids—I. Methanol and Carbon Dioxide Mixtures

Methanol can dissolve considerable amounts of CO2 under pressure. When this occurs, viscosity decreases and volume increases, which is a typical feature of expanded liquids. In this study, molecular dynamics (MD) simulations were conducted for methanol and CO2 mixtures at 50°C and high pressures to explore features of the expanded liquid state in terms of solution structure. Radial distribution function for methanol–methanol molecules showed that methanol molecules formed hydrogen bonds and nearest hydrogen bonds distance was not changed. The self-diffusion coefficients of both methanol and CO2 were found to decrease monotonically from the pure CO2 side and then not to change appreciably at methanol mole fractions higher than about 0.5. It should also be noted that the simulation results could qualitatively present the dielectric spectroscopy results reported in the literature. These results showed that methanol molecules make hydrogen bond networks and hydrogen bond networks surrounded CO2 molecules at mole fractions higher than about 0.5. Further addition of CO2 into methanol caused the hydrogen bond networks to break up and to form smaller hydrogen bond aggregates.

X-ray detection capabilities of plastic scintillators incorporated with hafnium oxide nanoparticles surface-modified with phenyl propionic acid

We synthesized plastic scintillators incorporated with HfO2 nanoparticles as detectors for X-ray synchrotron radiation. Nanoparticles with sizes of less than 10 nm were synthesized with the subcritical hydrothermal method. The detection efficiency of high-energy X-ray photons improved by up to 3.3 times because of the addition of the nanoparticles. Nanosecond time resolution was successfully achieved for all the scintillators. These results indicate that this method is applicable for the preparation of plastic scintillators to detect X-ray synchrotron radiation.