Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO2 Reduction with Nearly 100% CO Selectivity

Single metal atom photocatalysts have received widespread attention due to the rational use of metal resources and maximum atom utilization efficiency. In particular, N-rich amorphous g-C 3 N 4 is always used as a support to anchor single metal atoms. However, the enhancement of photocatalytic activity of g-C 3 N 4 by introducing a single atom is limited due to the bulk morphology and the excess defects of amorphous g-C 3 N 4 . Here, we report crystalline g-C 3 N 4 nanorod supported copper single atoms by molten salts and the reflux method. The prepared single Cu atoms/crystalline g-C 3 N 4 photocatalyst (Cu-CCN) shows highly selective and efficient photocatalytic reduction of CO 2 under the absence of any cocatalyst or sacrificial agent. The introduction of single Cu atoms can be used as the CO 2 adsorption site, thus increasing the adsorption capacity of Cu-CCN samples to CO 2 . Theoretical calculation results show that reducing CO 2 to CH 4 on Cu-CCN samples is an entropy-increasing process, whereas reducing CO 2 to CO is an entropy-decreasing process. As a result, the Cu-CCN samples exhibited enhanced photocatalytic CO 2 reduction with nearly 100% selective photocatalytic CO 2 to CO conversion. The mechanism of photocatalytic CO 2 reduction over Cu-CCN samples was proposed based on in situ Fourier transform infrared spectra, X-ray absorption spectroscopy, and density functional theory calculation. This work provides an in-depth understanding of the design of photocatalysts for enhancing active sites of the reactants.