Tantalate and mobate pyrochlores, Ca2M2O7 (M = Nb, Ta) and A(2)Ta(2)O(6) (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 H-2 and O-2 were achieved over tantalate pyrochlores loaded with a small amount of nickel oxide (NiO) as a catalyst for H2 production, while the NiO-loaded mobate 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. (c) 2005 Elsevier B.V. All rights reserved.