Preparation, characterization and photocatalytic property of nanosized K–Ta mixed oxides via a sol–gel method

Pyrochlore-type K2Ta2O6 compound cannot be obtained by a conventional solid-state reaction. Here, we report the synthesis of K2Ta2O6 and tetragonal tungsten bronze (TTB)-type K6Ta10.8O30 nanopowders using a facile and low-cost sol–gel method at low temperature. The as-prepared samples were characterized by XRD, TG-DSC, FESEM, UV–vis diffuse reflectance spectrum and XPS. The compound K2Ta2O6 was formed at 700 °C and reached complete crystallization at 750 °C, and decomposed into pure K6Ta10.8O30 with the volatilization of K2O at 900 °C. The transformation of K2Ta2O6 to K6Ta10.8O30 is reported for the first time. The band gap of the pure K2Ta2O6 and K6Ta10.8O30 samples was found to be about 4.16 and 3.63 eV, respectively. The as-prepared K2Ta2O6 sample exhibited an efficient photocatalytic activity for the decomposition of azo dye acid red G (ARG) and 4-nitrophenol (4-NP, a typical persistent organic pollutant) solution under UV irradiation. According to the experimental results, the mechanism of the photocatalytic reaction over K2Ta2O6 was discussed.