Recent modification, mechanisms, and performance of zinc oxide-based photocatalysts for sustainable dye degradation

The textile industry, which has crucial social and economic roles, faces sustainability challenges due to the generation of abundant wastewater contaminated by dyes. A wide range of photocatalysts has been developed to degrade dyes to reduce chemical and energy consumption in the treatment of dye-contaminated wastewater. This review mainly focuses on the photocatalytic mechanism and past studies of low-cost zinc oxide (ZnO) photocatalysts with various dopants to degrade dye degradation performance. Unlike previous reviews, this review delves deeply into property changes and possible mechanisms of ZnO-based photocatalysts induced by various dopants. ZnO-based photocatalysts are commonly doped with other semiconductors, metals, and non-metallic dopants. Semiconductor dopants such as titanium dioxide (TiO 2 ), graphitic carbon nitride (g-C 3 N 4 ), and iron oxide (Fe 2 O 3 ) significantly modify the band gap and broaden the spectral response range of ZnO photocatalysts. Metallic dopants, including silver (Ag), copper (Cu), and cobalt (Co), introduce plasmonic effects that enhance the electrical conductivity and photocatalytic activity. Conversely, non-metallic dopants, especially carbon nanomaterials and sulfur (S), enable the adjustment of the band gap and surface properties of ZnO. Photocatalytic coating and thin films should be developed for photocatalyst reuse in future works.