Advances in Composite Photocatalysts for Efficient Degradation of Organic Pollutants: Strategies, Challenges, and Future Perspectives

The persistent release of synthetic dyes such as methylene blue (MB) into aquatic environments poses a significant ecological hazard due to their chemical stability and toxicity. In recent years, the application of engineered composite photocatalysts has emerged as a potent solution for efficient dye degradation under visible and UV light. This review comprehensively summarizes various advanced composites, including carbon-based, metal-doped, and heterojunction materials, tailored for MB degradation. Notably, composites such as TiO2/C-550, WS2/GO/Au, and MOF-derived α-Fe2O3/ZnO achieved near-complete degradation (>99%) within 30–150 min, while others, like ZnO/JSAC-COO− and Ag/TiO2/CNT, displayed enhanced charge separation and stability over five consecutive cycles. Band gap engineering (ranging from 1.7 eV to 3.2 eV) and reactive oxygen species (·OH, ·O2−) generation were key to their photocatalytic performance. This review compares the structural attributes, synthetic strategies, and degradation kinetics across systems, highlighting the synergistic role of co-catalysts, surface area, and electron mobility. This work offers systematic insight into the state-of-the-art composite photocatalysts and provides a comparative framework to guide future material design for wastewater treatment applications.