Published papers

Surfactant-free coupling polymerization of pyrrole (Py) and its derivatives, namely, N-methylpyrrole (MPy) and N-ethylpyrrole (EPy), was conducted using solid Fe(NO3)3 in the presence of an aqueous medium, resulting in aqueous dispersions of polymer particles. Dynamic light scattering studies revealed the production of colloidally stable polymer nanoparticles with diameters of 153–206 nm, 262–294 nm and 273–278 nm in aqueous media for the Py, MPy and EPy systems, respectively. The particle sizes of poly(N-methylpyrrole) (PMPy) and poly(N-ethylpyrrole) (PEPy) were larger than those of polypyrrole (PPy), which could be due to the greater hydrophobicity of MPy and EPy than Py. The particles could achieve colloidal stability through an electrostatic stabilization mechanism, as the polymerization process introduces cationic charges to the polymers via doping. Larger amounts of hydroxy and carbonyl groups were introduced into PMPy and PEPy because of the easier overoxidation of MPy and EPy due to their lower redox potentials than that of Py. Furthermore, the resulting particles could adsorb on oil‒water interfaces and work as effective Pickering-type emulsifiers. Suspension polymerization of vinyl monomer-in-water Pickering emulsions stabilized with PPy and PMPy nanoparticles resulted in the production of nanoparticle-coated polymer microparticles with diameters of 25 μm and 154 μm, respectively.

Ultra-small metal particles having band gaps are regarded as a new class of functional materials. We investigated the size dependencies of the band-edge energies on Cu quantum-dots in the size range of 0.7-2.1 nm. The extremely high conduction band-edge energies owing to the strong quantum-size effects were observed for sizes below 1 nm.

Biogenic calcium oxalate monohydrate (COM, CaC2O4·H2O) needle crystals (raphides) having a pointed tip and two tails are arranged as a bundle in grape leaves. In this work, the specific hierarchical architecture was studied at the micrometric and nanometric scales. Raphides were macroscopically characterized as having a twin-like chiral configuration of COM divided by an organic central wall and covered with an organic enveloping membrane. The COM of the raphides has a mesocrystalline structure that consists of small grains ∼10 nm in diameter with a distorted single-crystal nature. The initially produced organic framework was suggested to control the specific crystal growth of COM under the construction of a raphide in a specific cell.

Titania is a competent photocatalyst widely used in environmental purification. Unfortunately, its photocatalytic ability to generate hydrogen by water decomposition without a co-catalyst is poor. Here, an efficient enhancement of noble-metal-free photocatalytic activity was studied on the basis of titania prepared in a supermicroporous silica template using TiCl3 aqueous solution as a precursor. The amount of evolved hydrogen increased sharply by 37 times as the concentration of TiCl3 was increased from 5 to 10 wt%. The existence of two species of titania was determined by XAFS analysis at concentrations of 10 wt% or greater. It is suggested that titania quantum dots inside the supermicropores and titania particles outside the supermicropores were prepared at the optimum precursor concentration and the resultant composite band structures suppressed electron–hole recombination.

We prepared conductive mixtures of Cu1.5Mn1.5O4 and Mn3O4 spinels (CMO–MOs) as positive electrode active materials in rechargeable Mg batteries (RMBs) using a sol–gel complex polymerization method. The CMO–MO spinel mixtures with high specific surface areas above 100 m2 g−1 were obtained with mild calcination in Ar at 300 °C. The conductivity of CMO–MOs was estimated to be approximately 1000 times higher than that of a conventional MgMn2O4 (MMO) spinel powder. The discharge capacities evaluated using 2032-type coin-cell battery with a Mg-alloy negative electrode at room temperature increase with an increase in the specific surface area of the spinel powders. The specific surface area for providing the theoretical capacity of the conductive CMO–MOs was about one-third that of the insulative MMO. High specific surface area and high conductivity are key parameters for the positive active material to realize practical room-temperature operation of RMBs.