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

Abstract

Tantalum(V) oxide (Ta2O5) powders were synthesized by a solvothermal reaction of tantalum pentabutoxide (TPB) in toluene at 473–573 K in the presence of water. Ta2O5 powder with a large surface area (>200 m2 g−1) was obtained at 473 and 523 K, and its X-ray diffraction patterns showed no clear peaks of crystallites, while crystalline β-phase Ta2O5 was obtained in the solvothermal process at 573 K. Post-calcination of the amorphous Ta2O5 at 973 K also induced crystallization into the β-phase. These amorphous and crystalline Ta2O5 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 β-phase samples exhibited negligible rates of hydrogen evolution, whereas crystalline β-phase samples formed by post-calcination showed higher activity. Calcination of amorphous Ta2O5 prepared by hydrolysis of TPB under atmospheric pressure also increased the rate, which is, however, ca. one third of that of Ta2O5 obtained ia 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 Ta2O5 exhibited a higher rate of CO2 formation than other Ta2O5 samples. Photoirradiation at >200 nm onto an aqueous 2-propanol suspension of platinized Ta2O5 under deaerated conditions yielded hydrogen and acetone in an early stage, but CO2 was liberated by prolonged irradiation, suggesting that decomposition of acetone to CO2 proceeds even under deaerated conditions.