Pyrochlore-like K₂Ta₂O₆ synthesized from different methods as efficient photocatalysts for water splitting

Pyrochlore-type K₂Ta₂O₆ with a high dielectric constant, which may lead to facile charge separation, is a prospective medium for photocatalytic water splitting. We synthesized K ₂Ta₂O₆ catalyst powders using sol-gel (SG) and hydrothermal (HT) methods. The Rietveld refinement simulation of the X-ray diffraction data shows that the SG catalyst has a lower density of ionic vacancy states and a more flattened Ta-O-Ta bond angle than the HT catalyst. Photoluminescence analysis indicates that the flattened Ta-O-Ta bond angle of the SG catalyst facilitates charge separation to suppress intrinsic recombination emission, and the lower vacancy density leads to a suppressed extrinsic defect emission. The SG catalyst has a higher photocatalytic water splitting activity, which is more than twice that of the HT catalyst under mercury lamp irradiation. The higher charge separation efficiency and lower electron-trapping vacancy density are responsible for the higher photocatalytic activity. The K₂Ta₂O₆ SG catalyst shows an apparent photocatalysis quantum yield which is superior to that of the well-documented NaTaO₃ catalysts. Our results suggest that K ₂Ta₂O₆ is a promising catalyst for use in photon energy conversion in various applications.