Boosting photocatalytic stability: hydrophilic Sr-doped ZnO thin films prepared via the SILAR method for enhanced performance over multiple cycles

Abstract This study deals with the synthesis and characterization of Sr-doped ZnO thin films with different concentrations (1, 3, 5, and 7 wt. %) using the SILAR method (Successive Ionic Layer Adsorption and Reaction). The main objective is to evaluate the effectiveness of the films as photocatalysts for the degradation of methylene blue under natural sunlight conditions. X-ray diffraction analysis confirms the polycrystalline nature of the films, with the crystallite size increasing with increasing Sr doping along the (100) plane. Morphological changes on the film surfaces are revealed by scanning electron microscopy and correlate with the increasing Sr content. Energy dispersive X-ray spectroscopy (EDX) confirms that there are no impurities in all films. 3D surface topography shows that higher Sr doping leads to an increase in average roughness and root mean square (Rq) values. Measurements of the water droplet contact angle (WDCA) indicate the hydrophilicity of the surface. Optical analysis shows that the absorption capacity of the films increases with Sr doping and shifts slightly towards longer wavelengths. Additionally, the band gap energy (Eg) shows a linear increment with higher Sr dopant concentrations. The unique contribution of this work lies in the careful investigation of the photocatalytic degradation of methylene blue using Sr-doped ZnO films as photocatalysts under natural sunlight. In particular, the films doped with 5 wt. % Sr show exceptional performance, achieving degradation rates of 94.82%, 94.61%, and 93.48% for the first, second, and third cycles, respectively. The novelty of these results lies in the successful synthesis of Sr-doped ZnO thin films by SILAR, the comprehensive characterization of their properties and the remarkable photocatalytic efficiency observed under real sunlight conditions. This work provides valuable insights into the potential application of these unique films for the efficient degradation of methylene blue, thus contributing to the further development of environmentally friendly photocatalytic materials.