Preparation and photocatalytic activity of ZnO/TiO2/SnO2 mixture

ZnO/TiO2/SnO2 mixture was prepared by mixing its component solid oxides ZnO, TiO2 and SnO2 in the molar ratio of 4ː1ː1, followed by calcining the solid mixture at 200–1300 °C. The products and solid-state reaction process during the calcinations were characterized with powder X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and Brunauer–Emmett–Teller measurement of specific surface area. Neither solid-state reaction nor change of crystal phase composition took place among the ZnO, TiO2 and SnO2 powders on the calcinations up to 600 °C. However, formation of the inverse spinel Zn2TiO4 and Zn2SnO4 was detected at 700–900 and 1100–1200 °C, respectively. Further increase of the calcination temperature enabled the mixture to form a single-phase solid solution Zn2Ti0.5Sn0.5O4 with an inverse spinel structure in the space group of Oh7-Fd3m. The ZnO/TiO2/SnO2 mixture was photocatalytically active for the degradation of methyl orange in water; its photocatalytic mass activity was 16.4 times that of SnO2, 2.0 times that of TiO2, and 0.92 times that of ZnO after calcination at 500 °C for 2 h. But, the mass activity of the mixture decreased with increasing the calcination temperature at above 700 °C because of the formation of the photoinactive Zn2TiO4, Zn2SnO4 and Zn2Ti0.5Sn0.5O4. The sample became completely inert for the photocatalysis after prolonged calcination at 1300 °C (42 h), since all of the active component oxides were reacted to form the solid solution Zn2Ti0.5Sn0.5O4 with no photocatalytic activity.

Graphical abstractComparison of the photocatalytic activities of ZnO, TiO2, SnO2 and ZnO/TiO2/SnO2 after the calcination at 500 °C for 2 h. Loading of the photocatalysts: 2.5 g/L; concentration of methyl orange: 20 mg/L .Figure optionsDownload full-size imageDownload as PowerPoint slide