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

The efficient conversion of CO 2 to carbon-neural fuels by photocatalysts can effectively address the increasingly prominent challenges of environmental pollution and energy shortage. TiO 2 is considered a promising photocatalyst. However, its disadvantages, such as poor adsorption of CO 2 and low carrier separation efficiency, inhibit its performance and selectivity in photocatalytic CO 2 reduction. Herein, K + -modified anatase TiO 2 ultrathin nanosheet photocatalysts were obtained via a reverse etching method using K 2 Ti 8 O 17 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 μmol·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 CH 4 was systematically investigated. The test results showed that during treatment with formic acid, a large amount of K + from the layered K 2 Ti 8 O 17 were removed and the original structure was destroyed. Therefore, highly dispersed TiO 2 nanosheets were obtained, with a small amount of K + remaining on the TiO 2 surface. The well-defined rectangular shapes of TiO 2 reduce the transmission distance of photogenerated carriers, whereas the presence of K + increase the chemisorption of CO 2 molecules, thereby activating CO 2 , promoting the conversion of bridge *CO to -CHO, and increasing CH 4 production. This study provides insightful references for the preparation and modification of traditional photocatalysts for photocatalytic CO 2 reduction reactions.