A Review of Visible-Light-Active Zinc Oxide Photocatalysts for Environmental Application

Zinc oxide (ZnO) photocatalysts have emerged as a promising material for environmental and energy applications due to their exceptional photocatalytic properties. Initially recognized for their efficiency under ultraviolet (UV) light, recent advancements have focused on enhancing ZnO's visible light activity (VLA) to address its inherent limitations. This review provides an overview of ZnO's structure, electronic properties, and photocatalytic mechanisms. Various strategies for modifying ZnO to harness visible light, including metal and non-metal doping, dye sensitization, and semiconductor coupling, are discussed. Special emphasis is placed on the mechanisms behind visible light absorption and reactive oxygen species (ROS) generation, as deduced through physicochemical and photoelectrochemical analyses. The applications of ZnO in environmental remediation are comprehensively explored, particularly for water treatment, disinfection, and air purification. The photocatalytic degradation of pollutants, including persistent organic compounds, pharmaceuticals, dyes, and pesticides, using ZnO is reviewed and compared with conventional UV-activated ZnO materials. This review underscores the potential of ZnO as an efficient and sustainable solution for environmental purification.