Sol–gel synthesis of ZnO–SiO2 thin films: impact of ZnO contents on its photonic efficiency

Highly crystalline ZnO–SiO2 films obtained by a sol–gel method at different ZnO contents were deposited on silicon substrate (P(100)) using spin coating process. The XRD results revealed that the strong ZnO(100) peak is grown with highly c-axis oriented film and the crystallinity is progressively improved with increasing ZnO contents. SEM micrographs of the films deposited on silicon substrate show a homogeneous and uniformity structure at different ZnO content. The prepared ZnO–SiO2 films are compared with either a film prepared from a commercial photocatalysts Hombikat UV-100 or Pilkington Glass Activ™ by the determination of their photonic efficiencies for degradation of methylene blue. The photocatalytic efficiency of the 10 wt% ZnO–SiO2 film was found to be about four times higher than film prepared from UV-100 or Pilkington Glass Activ™. The photocatalytic efficiencies of ZnO–SiO2 films are increased with increasing ZnO content from 1 wt% to 10 wt% ZnO and then decreased at 15 wt% ZnO. The order of photocatalytic efficiencies of ZnO–SiO2 films at different ZnO content and commercial photocatalysts after 6 h illumination were as following: 10 wt% ZnO > 15 wt% ZnO > 1 wt% ZnO > as-prepared 10 wt% ZnO–SiO2 film > UV-100 > Pilkington Glass Activ™, which suggested that the ZnO–SiO2 films are photoactive than commercial photocatalysts. The improved efficiency and potentially the low-cost synthesis suggest that this material might be practically useful as a photocatalyst film.