Optimal thickness and annealing temperature for enhancement of structural, optical, and photocatalytic properties of ZnO thin films

Abstract

Thin films of ZnO, with distinct thicknesses, were deposited on soda-lime glass substrates by sol–gel spin-coating as a cost-effective method without any evacuation facilities. The nanocrystalline structure of the deposited films was indexed by the atomic force microscope and X-ray diffraction techniques. The average grain size increases with the increase of the film thickness and annealing temperature. The energy-dispersive X-ray technique has been used to check the atomic ratios of Zn and O with the film thickness and heat treatment for homogeneous ZnO films. ZnO films show elevated transmission in the visible spectrum as a transparent semiconductor material. Optical constants, like absorption coefficient, optical band gap, and refractive index, were obtained by the Swanepoel method. All thin film samples were applied for photodegradation of reactive orange 96 (RO96) to evaluate the effect of thickness and annealing temperature on the ZnO film’s photocatalytic activity. ZnO 4L (400 °C, 3 h) film possesses the highest rate of photodegradation about 0.1 min⁻¹ for RO96 with high stability and reusability.