Synthesis, characterization and photocatalytic activity of KAl0.33W1.67O6 and Sn0.5Al0.33W1.67O6xH2O

Nano sized defect pyrochlore, KAl0.33W1.67O6 (KAW), is prepared through sol-gel method. Divalent tin-doped KAW is obtained at room temperature by ion exchange method using acidified SnCl2 and parent KAW. These materials are characterized by powder X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive spectra (SEM-EDS), Raman Spectroscopy and X-ray photo electronic spectroscopy. The composition of tin-doped KAW is obtained from chemical analysis, SEM-EDS and TGA methods and written as Sn0.5Al0.33W1.67O6xH2O (x = 1.4-1.5) (SnAW). It crystallizes in cubic lattice with Fd3¯m space group. The band gap energies are found to be 2.82 and 2.21 eV for KAW and SnAW respectively. The observed reduction in the band gap with the introduction of Sn(2+) in defect pyrochlore lattice is due to mixing of 5s state of Sn(2+) with O 2p states leading to an upward shift in the valence band. The Raman spectra of these materials gave more bands than the number expected for defect pyrochlores due to substitutional disorder in 16c sites and displacive disorder of A ions. The photoactivity of SnAW is higher compared to KAW.