Hybrid Ag@TiO₂ core-shell nanostructures with highly enhanced photocatalytic performance

A new synthetic approach has been developed to prepare silver@titanium dioxide (Ag@TiO₂) core-shell nanostructures with controllable size, shape, crystal phase and function at ambient conditions (e.g. in water, ≤100 ° C). This approach shows a few unique features, including short reaction time (a few minutes) for forming core-shell nanostructures, no requirement of high temperature calcinations for generating TiO₂ (e.g. at ∼100 ° C in our case), tunable TiO₂ shell thickness, high yield and good reproducibility. The experimental results show that the Ag@TiO₂ core-shell nanostructures exhibit excellent photocatalytic activity compared to the commercial TiO₂ (P25) and Ag-doped TiO₂ nanocomposite in the degradation of organic dye molecules (e.g. methyl orange) with ultraviolet (UV) irradiation. This could be attributed to the large surface area of TiO₂ nanoparticles for maximum harvesting of UV light, mixed anatase and rutile crystalline phases in the TiO₂ shell and the effective charge separation between Ag and TiO₂ that can reduce the possible recombination of electron-hole (e^--h⁺) pairs within TiO₂ generated under UV radiation. To further understand the charge separation situation within Ag-TiO₂ composites, theoretical simulation (e.g. density functional theory, DFT) was employed in this study. The DFT simulation results indicate that for the Ag@TiO₂ core-shell nanostructures, photo-generated electrons transfer readily from the external TiO₂ layer to the internal Ag layer with heavy accumulation compared to those doping Ag on TiO₂ surfaces, which may reduce the recombination of e^--h⁺ pairs and thus enhance the photocatalytic efficiency. The findings may open a new strategy to synthesize TiO₂-based photocatalysts with highly enhanced efficiency for environmental remediation applications.