Enhancing CO Selectivity in CO₂ Photoreduction via Local Hydrophobic Modifications in S-Scheme Heterojunctions

To address the challenge of competitive H 2 O adsorption in photocatalytic CO 2 reduction, localized hydrophobicity-modified S-scheme heterojunctions (WS/o-CN) were synthesized by combining WS 2 and g-C 3 N 4, which was modified by the addition of CTAB. Structural characterization and contact angle testing confirmed the formation of S-scheme heterojunctions and the specific structural role of CTAB. The optical, electrochemical properties, and gas adsorption capacity of the catalysts were analyzed, followed by in situ XPS and fs-TA tests to investigate the energy band structure and electron transfer paths. These results showed that localized hydrophobic modification reduces the surface proton concentration while maintaining efficient electron–hole separation in the S-scheme heterojunction. Testing the photocatalytic activity of WS/o-CN showed that the yield of CO reached 23.24 μmol g –1 h –1 with a high selectivity of 74.7%. Combined with molecular dynamics simulations and in situ DRIFTS tests, the results demonstrated that the introduction of the nonpolar long carbon chain CTAB effectively inhibits the adsorption of heterogeneous H 2 O on the catalyst surface while enhancing the maximum adsorption of CO 2 . The localized hydrophobicity reduces the proton concentration on the surface of g-C 3 N 4, which in turn suppresses the absorption of photogenerated electrons by the HER reaction. This facilitates the efficient and selective conversion of CO 2 to CO. This study highlights a surface engineering strategy that couples electronic structure optimization with interfacial wettability control, providing valuable insights into the design of selective and efficient photocatalysts for CO 2 -to-CO conversion.