Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO 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-CN is always used as a support to anchor single metal atoms. However, the enhancement of photocatalytic activity of g-CN by introducing a single atom is limited due to the bulk morphology and the excess defects of amorphous g-CN. Here, we report crystalline g-CN nanorod supported copper single atoms by molten salts and the reflux method. The prepared single Cu atoms/crystalline g-CN photocatalyst (Cu-CCN) shows highly selective and efficient photocatalytic reduction of CO under the absence of any cocatalyst or sacrificial agent. The introduction of single Cu atoms can be used as the CO adsorption site, thus increasing the adsorption capacity of Cu-CCN samples to CO. Theoretical calculation results show that reducing CO to CH on Cu-CCN samples is an entropy-increasing process, whereas reducing CO to CO is an entropy-decreasing process. As a result, the Cu-CCN samples exhibited enhanced photocatalytic CO reduction with nearly 100% selective photocatalytic CO to CO conversion. The mechanism of photocatalytic CO reduction over Cu-CCN samples was proposed based on 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.