Photocatalytic Nanomaterials for the Degradation of Organic Pollutants in Wastewater: A Review of Mechanisms, Efficiencies, and Synergistic Approaches

Industrial and municipal wastewater contains high levels of persistent organic pollutants, which represent a severe threat to the environment and water security. Therefore, developing new and innovative treatment technologies that are capable of fully mineralizing these pollutants is needed. Heterogeneous photocatalysis using semiconductor nanomaterials has become one of the most promising advanced oxidation processes to address this problem by providing sustainable, environmentally friendly methods for degrading organic pollutants under solar irradiation. The comprehensive review provides an overview of photocatalytic nanomaterials for the treatment of wastewater, systematically reviewing their mechanism, materials used, and the various means of enhancing their performance through synergism. The review will first discuss the principles of the photocatalytic process using semiconductors with respect to the band structure, charge carrier dynamics and generation of reactive oxygen species (ROS) followed by a critical analysis of the factors affecting the efficiency of photocatalytic reactions. The materials covered will include benchmark metal oxides such as TiO₂, ZnO, WO₃, and Fe₂O₃ and visible-light-active materials such as metal sulfides, bismuth-based compounds, and graphitic carbon nitride. Each photocatalyst will be analyzed for advantages and disadvantages as well as efficiencies as they relate to the degradation of pollutants. Finally, the review will cover the development of synergistic enhancements to address the inherent limitations of photocatalytic materials, which include but are not limited to metal and non-metal doping, Type-II and Z-scheme heterojunctions, carbon-based nanocomposites, and integration with adsorption, Fenton chemistry and photo electrocatalysis. Finally, current challenges impeding practical implementation—scalability, stability, selective degradation, and the need for techno-economic and life cycle assessments—are critically examined, alongside future directions encompassing machine learning-guided material discovery, novel photocatalysts, and process integration. By synthesizing recent literature and identifying key research priorities, this review aims to guide the rational design of efficient, stable, and scalable photocatalytic systems for real-world water purification.