Visible light-sensitive mesoporous N-doped Ta2O5 spheres: synthesis and photocatalytic activity for hydrogen evolution and CO2 reduction

Crystallized mesoporous tantalum pentoxide spheres (CMTS) with particle diameters of ca. 100-500 nm and composed of Ta2O5 nanocrystals were synthesized for the first time by a combination of the sol-gel process and heat-treatment with the aid of carbon reinforcement. The specific surface area of the CMTS was up to 105 m(2) g(-1) and the pore diameter was controllable in the range of 5.6-17 nm by changing the crystallization temperature. Visible light-sensitive p-type N-doped Ta2O5 (N-CMTS) containing 5 at% N was successfully obtained by treatment of CMTS with ammonia, while retaining the mesoporosity and morphology of CMTS. N-CMTS exhibited excellent photocatalytic activity for hydrogen evolution and CO2 reduction (with ruthenium-complex) under visible light irradiation (>= 410 nm) due to their larger surface area and controlled morphology compared with previously reported N-doped Ta2O5 fine particles.