Enhancing the Photocatalytic Activity and Antibacterial Efficiency of TiO₂ Nanosheets via Doping with Ag, Cu, or Ce

TiO2 nanomaterials are well-known for their effective photocatalytic properties, with broad practical applications. In this study, to suppress electron–hole recombination and enhance photocatalytic performance, we synthesized highly ordered TiO2 nanosheets with exposed [001] facets and subsequently doped them with Ag, Cu, or Ce via photodeposition. Electron spin resonance analysis confirmed that all doped TiO2 nanosheets produced higher amounts of reactive oxygen species compared to undoped TiO2 nanosheets, indicating improved charge separation induced by metal dopants. To further evaluate their photocatalytic performance, we conducted methylene blue degradation assays and antibacterial tests against Streptococcus mutans. Ag-doped TiO2 nanosheets showed UV-induced methylene blue desorption in the methylene blue degradation assays. This behavior is attributed to the trapping of low-energy electrons by Ag, which weakens the interaction with adsorbed methylene blue and facilitates rapid back-electron transfer upon UV irradiation, ultimately leading to methylene blue photodesorption. In antibacterial tests, Cu-doped TiO2 nanosheets exhibited markedly enhanced photocatalytic antibacterial efficiency. This enhancement is attributed to the presence of CuO, which forms a p–n heterojunction with TiO2, thereby promoting effective charge separation and facilitating photocatalytic oxidation processes. These findings provide deeper insight into the physicochemical and photochemical roles of Ag, Cu, and Ce dopants in modulating surface adsorption and charge dynamics in TiO2-based materials. While Ag, Cu, and Ce serve as electron sinks facilitating charge separation, they can also lower electron energy, impeding electron transfer to O2. Notably, CuO’s formation of a p–n heterojunction with TiO2 creates more efficient photocatalytic pathways. Overall, this study advances our understanding of metal-doped TiO2 photocatalysts and supports their potential applications in dental materials, environmental remediation, and biomedical devices.