Synthesis, Mesostructure, and Photocatalysis of a Highly Ordered and Thermally Stable Mesoporous Mg and Ta Mixed Oxide

An ordered (2D-hexagonal) mesoporous Mg and Ta mixed oxide (Mg-Ta oxide) is successfully prepared. The mesoporous Mg-Ta oxide is stable after calcination at 773 K for 30 h, and has a BET surface area of 123 m2 g-1, pore size of 5.0 nm, and wall thickness of 2.8 nm. Removal of the template by washing in water results in a wormhole-like microporous material with a BET surface area of 424 m2 g-1. The ordered mesoporous structure is not achieved after aging alone (313 K), but becomes complete through structural rearrangement in the initial stage of calcination (<423 K) for template removal. The presence of the template during calcination is found to be indispensable, and the ordered mesoporous material is not obtained when the template is removed by washing with water prior to calcination. Although the inorganic phase is amorphous, the photocatalytic activity for overall water decomposition over the 2D hexagonal mesoporous Mg-Ta oxide is much higher than over crystallized MgTa2O6. The highest activity (ca. 100 (mu)mol h-1 for H2 and 50 mol h-1 for O2) is attained by loading with 0.1 wt % NiO followed by reduction and reoxidation pretreatment.