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

Niobium(v) oxide (Nb2O5) powders were synthesized by the solvothermal react ion 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 m(2) 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 s pectrum 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 wa ter used in the synthetic procedure induced crystallization of Nb2O5 into t he TT-phase. The surface area of the solvothermal products decreased with i ncreases in the amount of water used, indicating growth of particles via wa ter-induced extension of the Nb-O-Nb network. These Nb2O5 particles were pl atinized 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 t han that of the crystalline Nb2O5 samples or other amorphous Nb2O5 samples supplied as niobic acid (Nb2O5. nH(2)O) 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 c onditions. The amorphous Nb2O5 samples, especially catalysts prepared by th e solvothermal method, exhibited a rate of carbon dioxide formation much hi gher than that of the crystalline Nb2O5 samples also used in this photocata lytic reaction system.