Facile Room Temperature Ion-Exchange Synthesis of Sn2+ Incorporated Pyrochlore-Type Oxides and Their Photocatalytic Activities

Abstract

Ion-exchange reactions of aqueous SnCl(2).2H(2)O solutions with oxides such as H(2)Sb(2)O(6).3.0H(2)O, KSbWO(6), and KTaWO(6).1.0H(2)O resulted in novel Sn(2+) incorporated pyrochlore-type oxides under ambient conditions. Characterization of the Sn(2+) exchanged products by powder X-ray diffraction, EDAX, thermogravimetric analysis, and chemical analysis yielded nominal compositions of Sn(0.92)Sb(2)O(6).2.0H(2)O, K(0.59)Sn(0.20)SbWO(6).1.0H(2)O, and K(0.58)Sn(0.29)TaWO(6).1.0H(2)O. Diffuse reflectance spectra of the oxides incorporated with Sn(2+) ions clearly exhibited red shifts from their respective parent oxides. The observed reduction in the band gaps to an extent of 0.9-1.6 eV was consistent with the Sn(2+) ion-exchange, and indicated the upward shifting of the valence band resulting from the contribution of 5s band of Sn(2+) to the O 2p band. Photocatalytic activities of the synthesized pyrochlore oxides were consistent with their electronic properties and decomposed methyl orange (MO) solutions under visible light. The pseudo first order rate constants of the oxides Sn(0.92)Sb(2)O(6).2.0H(2)O and K(0.59)Sn(0.20)SbWO(6).1.0H(2)O for the decomposition of MO solutions were found to be 1.34 h(-1) and 0.217 h(-1), respectively, and almost a negligible MO decomposition was observed for K(0.58)Sn(0.29)TaWO(6).1.0H(2)O. The photocatalytic efficiencies of the oxides were found to be proportional to the rate of formation of .OH radicals, which was found to vary in the order, Sn(0.92)Sb(2)O(6).2.0H(2)O > K(0.59)Sn(0.20)SbWO(6).1.0H(2)O > K(0.58)Sn(0.29)TaWO(6).1.0H(2)O as determined by the photoluminescence spectra using terephthalic acid.