Chloride-doped ZnO thin films prepared by spray pyrolysis: Effects on microstructural, optical, and photocatalytic properties

This study discusses the effects of chloride doping on the photocatalytic properties of ZnO thin films, evaluated under UV-A radiation (365 ± 5 nm) using acetaminophen as a model reactant. Zinc oxide (ZnO) thin films doped with chloride anions were prepared by spray pyrolysis. The films were homogeneous, stable to hydrodynamic forces, and photocatalytically active. The doping procedure affected the photoactivity of the semiconductor, its light absorption properties and the morphology of the surface, and promoted a redshift of the absorption edge. The microstructure of the films showed a positive correlation between the concentration and the degree of particle agglomeration; however, the higher content of chloride also promoted higher porosity. The undoped ZnO films exhibited the best photocatalytic performance under the investigated conditions. By comparing this work with the recent literature on the use of ZnO in the photocatalytic oxidation of acetaminophen, it was found that the synthesized ZnO films have better energetic efficiency (EE0,med = 9.91 kWh L−1) and provide similar quantum yields (φmed = 6.84 × 10−4 mol E−1). Finally, a segregation study indicates that grain-boundary segregation has a strong impact on photocatalytic efficiency, offering a sustainable and low cost alternative for designing ZnO-based photocatalysts.