Photocatalytic activity of hydrothermally synthesized tantalate pyrochlores for overall water splitting

Tantalate and niobate pyrochlores, Ca2M2O7 (M = Nb, Ta) and A2Ta2O6 (A = Na, K), were prepared by a hydrothermal method. These oxides were crystallized directly from tantalum or niobium alkoxide in the presence of sodium, potassium or calcium cation in basic solutions at temperatures between 373 and 448 K, and their crystallinity was improved by calcination in air. Stoichiometric liberations of H2 and O2 were achieved over tantalate pyrochlores loaded with a small amount of nickel oxide (NiO) as a catalyst for H2 production, while the NiO-loaded niobate pyrochlore showed no photocatalytic activity. The photocatalytic functions of the tantalate pyrochlores were attributed to their energy levels of the bottom of conduction bands being much more negative than those of the niobate pyrochlores.