Transition metal phosphosulfides (TMPSs) have gained much interest due to their highly enhanced photocatalytic activities compared to their corresponding phosphides and sulfides. However, the application of TMPSs on photocatalytic CO2 reduction remains a challenge due to their inappropriate band positions and rapid recombination of photogenerated electron–hole pairs. Herein, we report ultrasmall copper phosphosulfide (us-Cu3P|S) nanocrystals anchored on 2D g-C3N4 nanosheets. Systematic studies on the interaction between us-Cu3P|S and g-C3N4 indicate the formation of an S-scheme heterojunction via interfacial P–N chemical bonds, which acts as an electron transfer channel and facilitates the separation and migration of photogenerated charge carriers. Upon the composite formation, the band structures of us-Cu3P|S and g-C3N4 are altered to enable the enhanced photocatalytic CO generation rate of 137 μmol g–1 h–1, which is eight times higher than that of pristine g-C3N4. The unique phosphosulfide structure is also beneficial for the enhanced electron transfer rate and provides abundant active sites. This first application of Cu3P|S to photocatalytic CO2 reduction marks an important step toward the development of TMPSs for photocatalytic applications.

ZnS is one of the promising earth-abundant catalysts for photoreduction reactions. The performance of ZnS in CO2 reduction is, however, limited because of its wide band gap, fast recombination of charge carriers, as well as low product selectivity due to the competing hydrogen evolution reaction (HER). Herein, Cu-doped ZnS containing abundant sphalerite and wurtzite phase (S–W) junctions is prepared and an enhanced photocatalytic activity with high selectivity in CO production is demonstrated. Both experimental and theoretical results reveal that Cu incorporation and the S–W phase junction enhance light absorption and promote photocatalytic activity. The presence of a Cu ion contributes to the CO generation and suppresses the competing HER by enhancing the bonding of the catalyst surface with •CO adsorbates. This work provides useful insights into the modification of CO2 reduction photocatalysts to realize high catalytic efficiency and product selectivity.