Ag-Doped hollow Multi-Shelled structure TiO₂ for highly selective photocatalytic CO₂ reduction

The photocatalytic conversion of CO₂ into valuable CH₄ offers a sustainable solution to pressing environmental and energy challenges. However, this process is hindered by several factors, including the low adsorption and activation of CO₂, rapid recombination of photogenerated charge carriers, and limited selectivity. Herein, hollow multi-shelled Ag-doped TiO₂ (Ag/TiO₂) nanospheres were successfully synthesized for highly selective photocatalytic CO₂ methanation. Time-resolved photoluminescence (TRPL) analysis reveals that Ag doping extends the carrier lifetime from 1.32 ns to 49.11 ns, effectively suppressing recombination. X-ray photoelectron spectroscopy (XPS) confirms that Ag doping leads to a redistribution of electron at Ag and Ti sites, thereby optimizing the adsorption of CO₂ on the catalyst. Density functional theory (DFT) calculations indicate that Ag doping strengthens CO₂ adsorption (the adsorption energy from -1.54 to -2.04 eV) and affects the desorption of intermediates, thereby altering the reaction products to favor the production of CH₄ instead of CO. Moreover, the hollow multi-shelled structure endows Ag/TiO₂ with a large specific surface area (142.4 m²/g), which is conducive to the adsorption and activation of CO₂. Consequently, the CH₄ yield of Ag/TiO₂ reached 89.51 μmol·g^-1·h^-1, which is approximately 6 times greater than that of pristine TiO₂. Additionally, the selectivity for CH₄ improved to 95 %. These findings highlight the potential of Ag-doped TiO₂ for efficient CO₂ photoreduction.