Synergistic roles of Ag+and Ag0 in TiO2:Ag photocatalyst for enhanced solar-driven degradation of mixed dye pollutants

The degradation of organic dyes is not only an environmental concern but also a platform for exploring charge-carrier dynamics in photocatalytic nanomaterials. Here, we investigate the impact of Y, Au, and Ag doping on the electronic and optical properties of hydrothermally synthesized TiO₂ nanoparticles and their relation to solar-driven photocatalysis. Among the samples, TiO₂:Ag exhibits the most pronounced activity, achieving >93 % removal of rhodamine B, methyl orange, and methylene blue in both single- and mixed-dye systems under natural sunlight (∼830 W/m²). This superior performance originates from the coexistence of Ag⁺ dopants and plasmonic Ag⁰species: Ag⁺introduces intermediate states that narrow the bandgap and extend visible-light absorption, while metallic Ag⁰forms Schottky junctions and supports localized surface plasmon resonance, thereby enhancing charge separation and prolonging carrier lifetimes. The synergy between Ag⁺and Ag⁰establishes a fundamental mechanism for efficient photocarrier generation, transport, and utilization in semiconductor photocatalysts. These findings provide physics-based insight into dopant–plasmon interactions and band-structure engineering, offering generalizable design principles for visible-light-active photocatalysis and optoelectronic applications.