Au Single Atom Supported on TiO2 Drives Hole Mitigation for the Enhanced Photooxidation of Hg0

Abstract

Noble metal-supported TiO2 has excellent photocatalytic activity for the oxidation of Hg0 due to the Mott–Schottky barrier that prevents the recombination of photogenerated hole–electron pairs. However, surface noble-metal atoms usually cause low atomic utilization, of which the inner layer cannot participate in the oxidation and is hence not beneficial for improving the photocatalytic activity. Single-atom-based catalysts (SAC) have an extreme atomic efficiency, reducing the amount of noble metals and significantly improving photocatalytic activity. Herein, 0.1% Au single atom (SA)-doped Ti4+ defect TiO2 (0.1% Au–Ti1-xO2) with Au–(O)4 coordination was used for the photooxidation of Hg0. Second, the influence of the coordination on the separation of photogenerated electron–hole pairs, the transfer direction of charges, and the oxidation of Hg0 was thoroughly explored using transient photovoltage (TPV), in situ X-ray photoelectron spectroscopy (XPS), density functional theory (DFT), etc. Finally, the influence of SO2 and NO on the photooxidation of Hg0 was discussed using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). 0.1% Au–Ti1-xO2 had a much higher photooxidation efficiency of Hg0 than 0.1% Au/TiO2. Moreover, the Au–(O)4 coordination significantly promoted the separation of photogenerated electron–hole pairs by driving the mitigation of photogenerated holes. Additionally, 0.1% Au–Ti1-xO2 exhibited a remarkable resistance to SO2 and NO because Au SA effectively avoided the deposition of nitrates and sulfates. This study provides a valuable surface engineering strategy for the atomic-level dispersion of noble metal-modified TiO2.