Abstract

Niobium(V) oxide (Nb₂O₅) powders were synthesized by the solvothermal reaction of niobium(V) pentabutoxide (NPB) in toluene at 573 K in the absence or presence of water. Nb₂O₅ powder with a large surface area (>200 m² g⁻¹) was obtained in the absence or presence of only a small amount of water. Its X-ray diffraction (XRD) pattern showed no clear peaks, and the Raman spectrum suggested formation of an Nb–O–Nb network, i.e., an amorphous Nb₂O₅ structure without long-range order. A further increase in the amount of water used in the synthetic procedure induced crystallization of Nb₂O₅ into the TT-phase. The surface area of the solvothermal products decreased with increases in the amount of water used, indicating growth of particles via water-induced extension of the Nb–O–Nb network. These Nb₂O₅ particles were platinized and then used for photocatalytic dehydrogenation of methanol in an aqueous solution under deaerated conditions. The amorphous Nb₂O₅ produced by the solvothermal process exhibited a rate of hydrogen evolution higher than that of the crystalline Nb₂O₅ samples or other amorphous Nb₂O₅ samples supplied as niobic acid (Nb₂O₅·nH₂O) and those prepared by hydrolysis of NPB under atmospheric conditions. Photocatalytic mineralization of acetic acid in aqueous solution was also conducted with bare Nb₂O₅ under aerated conditions. The amorphous Nb₂O₅ samples, especially catalysts prepared by the solvothermal method, exhibited a rate of carbon dioxide formation much higher than that of the crystalline Nb₂O₅ samples also used in this photocatalytic reaction system.