Solvothermal synthesis of tantalum(V) oxide nanoparticles and their photocatalytic activities in aqueous suspension systems

Tantalum(v) oxide (Ta(2)O(5)) powders were synthesized by a solvothermal reaction of tantalum pentabutoxide (TPB) in toluene at 473-573 K in the presence of water. Ta(2)O(5) powder with a large surface area (> 200 g(-1)) was obtained at 473 and 523 K, and its X-ray diffraction patterns showed no clear peaks of crystallites, while crystalline beta -phase Ta(2)O(5) was obtained in the solvothermal process at 573 K. Post-calcination of the amorphous Ta(2)O(5) at 973 K also induced crystallization into the beta -phase. These amorphous and crystalline Ta(2)O(5) particles were platinized and then used for photocatalytic production of hydrogen from 2-propanol in aqueous solution under deaerated conditions by irradiation at a wavelength > 300 nm. As-synthesized amorphous and crystalline beta -phase samples exhibited negligible rates of hydrogen evolution, whereas crystalline beta -phase samples formed by post-calcination showed higher activity. Calcination of amorphous Ta(2)O(5) prepared by hydrolysis of TPB under atmospheric pressure also increased the rate, which is, however, ca. one third of that of Ta(2)O(5) obtained via the solvothermal route. Mineralization of acetic acid under aerated conditions was conducted as a test reaction for photocatalytic decomposition of organic compounds. Also, in this reaction system, bare (not platinized) solvothermal Ta(2)O(5) exhibited a higher rate of CO(2) formation than other Ta(2)O(5) samples. Photoirradiation at > 200 nm onto an aqueous 2-propanol suspension of platinized Ta(2)O(5) under deaerated conditions yielded hydrogen and acetone in an early stage, but CO(2) was liberated by prolonged irradiation, suggesting that decomposition of acetone to CO(2) proceeds even under deaerated conditions.