Efficient photocatalytic CO2 methanation via promoted conversion of bridge *CO over surface K+ on ultrathin TiO2

The efficient conversion of CO2 to carbon-neural fuels by photocatalysts can effectively address the increasingly prominent challenges of environmental pollution and energy shortage. TiO2 is considered a promising photocatalyst. However, its disadvantages, such as poor adsorption of CO2 and low carrier separation efficiency, inhibit its performance and selectivity in photocatalytic CO2 reduction. Herein, K+-modified anatase TiO2 ultrathin nanosheet photocatalysts were obtained via a reverse etching method using K2Ti8O17 as the precursor. The selectivity of the optimized photocatalyst for methane was 96.02% in a gas-solid system without additives, with an excellent photocatalytic rate of 42.3 mu mol.g(-1).h(-1), which was 3.39 times higher than that of P25. The effects of K+ on photocatalytic behaviors and the selectivity of CH4 was systematically investigated. The test results showed that during treatment with formic acid, a large amount of K+ from the layered K2Ti8O17 were removed and the original structure was destroyed. Therefore, highly dispersed TiO2 nanosheets were obtained, with a small amount of K+ remaining on the TiO2 surface. The well-defined rectangular shapes of TiO2 reduce the transmission distance of photogenerated carriers, whereas the presence of K+ increase the chemisorption of CO2 molecules, thereby activating CO2, promoting the conversion of bridge *CO to -CHO, and increasing CH4 production. This study provides insightful references for the preparation and modification of traditional photocatalysts for photocatalytic CO2 reduction reactions.