Recent progress of Ag/TiO2 photocatalyst for wastewater treatment: Doping, co-doping, and green materials functionalization

Surface modification via doping or functionalization is one of the most commonly applied approaches for addressing the innate limitations of TiO2 photocatalysts. Amongst numerous dopants, silver (Ag) has been regarded as an efficient strategy to retard electron holes recombination due to the formation of the Schottky barrier on the TiO2 interface and extending absorption to the visible region. This review primarily focuses on discussing and evaluating the recent progress in the modification of Ag/TiO2 via co-doping with non-metals and transition metals, as well as the synthesis strategies that have been applied in engineering the materials. The effects of doping and co-doping on the induced chemical and physical properties, photocatalytic performance, stability, and recyclability aspects have also been highlighted. This review also examines the potential improvement of Ag/TiO2 through the addition of green materials such as plant-based materials (cellulose-derived composites, chitosan, alginate), ceramic materials (clay, kaolin bentonite), and also ionic liquid green solvent. Recommendations for further research opportunities, limitations, and challenges have also been suggested.