Synthesis and photocatalytic property of triple-layered perovskite compounds, A2Ca4TaxNb6-xO20 (A = K, H; x = 0, 2, 3, 4, and 6)

New layered perovskites, K2Ca4TaxNb6-xO20 (x = 0, 2, 3, 4, and 6), were synthesized by a conventional solid-state reaction. The crystal structures were refined from powder X-ray diffraction (XRD) patterns as new members of the Dion-Jacobson-type series. Based on K2Ca4TaxNb6-xO20, new reduced layered perovskites, H2Ca4TaxNb6-xO20 (x = 0, 2, 3, 4, and 6), were synthesized by an ion exchange reaction from the parent potassium compounds, K2Ca4TaxNb6-xO20. The interlayer distances, band gap energies, and photocatalytic activities of H2Ca4TaxNb6-xO20 depended on the x value (the ratio of Ta to Nb). When x = 2, H2Ca4Ta2Nb4O20 showed the best photocatalytic activity. Using H2Ca4Ta2Nb4O20 as a catalyst, the photocatalytic H2 evolution rate reached 8.5 mmol h-1 g-1 in 10 vol.% methanol aqueous solution under irradiation with wavelength more than 290 nm from a 100-W mercury lamp