Novel solvothermal synthesis of niobium(v) oxide powders and their photocatalytic activity in aqueous suspensions

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.