Preparation and characterization of ZnO-SiO2 thin films as highly efficient photocatalyst

ZnO doped SiO2 thin films were prepared by the sol-gel method and annealed at different temperatures from 200 to 1100 degrees C. SiO2 matrix is selected as support due to their high flexibility, thermal stability and high porosity and surface areas. The XRD patterns showed that the hexagonal wurtzite structure of the ZnO film was formed for all the prepared samples. TEM images of ZnO synthesized nanoparticles are almost spherical with a relatively narrow size distribution in the range of 5-20 nm according to the annealing temperature. These images clearly show the (0 0 0 1) atomic planes (interplanner distance is 0.52 nm) perpendicular to the c-axis, thus indicating that (0 0 0 1) is the preferred growth direction of these wurtzite-type ZnO. The newly prepared photocatalysts ZnO-SiO2 films have been evaluated by the determination of their photonic efficiencies for degradation of methylene blue. The photonic efficiencies of 10 wt% ZnO-SiO2 increase from 0.9 to 2.3% with increasing annealing temperature from 200 to 600 degrees C and then gradually decrease to 1.56% at 1100 degrees C. The results indicate that 10 wt% ZnO-SiO2 annealed at 600 degrees C showed the highest photocatalytic activity for the MB photodegradation. Our work demonstrates the ability to reduce the working temperature as well as to increase the response of ZnO thin film as a highly efficient photocatalyst, which would be of great merit for commercialized applications. (C) 2013 Elsevier B.V. All rights reserved.