Waste-Derived Photocatalysts for Light-Driven Water Treatment: A Comprehensive Review of Green Materials from Agri-Food, Industrial, and E-Waste

The growing prevalence of emerging contaminants in the aquatic environment poses a critical challenge to global water security. Conventional treatment methods often fail to remove persistent pollutants, necessitating the development of sustainable and efficient alternatives. Heterogeneous photocatalysis, one of the advanced oxidation processes, driven by the light-induced generation of reactive species, has emerged as a promising solution. However, the high cost and environmental footprint of conventional photocatalysts limit large-scale implementation. This review explores the innovative use of waste-derived materials, originating from agricultural residues, industrial by-products, food waste, and electronic waste, as green precursors for photocatalyst synthesis. These materials offer unique structural and chemical properties, including a high surface area, tunable bandgaps, and enhanced stability, while supporting circular economy principles. Recent advances in synthesis strategies, performance optimization, and hybrid system integration are critically analyzed, alongside challenges related to scalability, environmental safety, and process standardization. Waste-to-resource approaches in photocatalysis represent a transformative pathway toward sustainable water treatment and resource recovery.