Influence of annealing temperature on the photocatalytic efficiency of sol-gel dip-coated ZnO thin films in methyl orange degradation

• ZnO thin films were deposited on glass and Si wafers by sol-gel method. • ZnO films annealing conditions affect structural and photocatalytic activity. • The highest photocatalytic activity was observed to ZnO films heat treated at 450 °C. • A > 90% MO degradation was obtained after 300 min of solar radiation exposure. ZnO thin films on glass substrates and silicon wafers were prepared by the sol-gel dipcoating technique and annealed at temperatures ranging from 300 - 550 °C. X-ray diffraction (XRD) and Raman analysis confirm the hexagonal wurtzite structure of ZnO. Scanning electron microscopy (SEM) examination confirmed that the films were homogeneous, crack-free and with a uniform distribution of nano-sized spherical grains. The decomposition of methyl orange (MO) using a solar simulator was used to determine the photocatalytic activity of the thin films. The annealing temperature was found to have a significant influence on the structure, morphology, and photocatalytic performance of ZnO thin films. The best photocatalytic activity under solar irradiation was shown by the ZnO thin film annealed at 450 °C. The enhanced photocatalytic performance of the films can be attributed to their optimized crystallinity, surface roughness and morphology, which provide more active sites for the photocatalytic reactions.