New approach for designing wrinkled and porous ZnO thin films for photocatalytic applications

Abstract

A new template-free, porous, and wrinkled ZnO thin films were designed by sol-gel dip-coating technique for enhancing the photocatalytic degradation of organic pollutants in water. The spontaneous formation of such nanostructure represents a certain type of instability-driven organization under intrinsic stress, such as thermal compression. The surface evolution was tracked by in situ thermo-ellipsometry technique through the changes in the film's thickness and refractive index. The engineered nanostructure was obtained by a pre-heat treatment at 150 ⁰ C in the infrared chamber of the dip-coater followed by a post-annealing in the air at 450 ⁰ C for 1 h. A wrinkled structure with a porosity of ∼ 22–25% and an average pore Ferret diameter of ∼24 nm were revealed, promoting the adsorption of pollutants onto the films' surface. The photocatalytic activity of ZnO films was tested via the degradation of methylene blue probe molecule under two different irradiation sources. A high removal efficiency above 92% and degradation rate constants of 0.0049 min−1 and 0.0121 min−1 were registered under UVA and visible light respectively.