Engineering a W18O49/Au/g-C3N4 S-scheme heterojunction for efficient photocatalytic CO2 reduction

Photocatalytic CO 2 reduction (CO 2 PR) offers a promising route for solar-to-fuel conversion and CO 2 valorization. However, practical photocatalytic applications are limited by rapid recombination of photogenerated carriers and restricted light utilization. Herein, a series of Au-modified W 18 O 49 /g-C 3 N 4 (WAC-X) heterojunction photocatalysts were constructed via a hydrothermal-calcination method. The optimized WAC-3 sample delivered CO and CH 4 yields of 114.67 and 85.75 μmol·g −1 ·h −1 , respectively, substantially higher than those of pure g-C 3 N 4 . Systematic characterization supports the formation of a built-in electric field at the heterojunction interface, which facilitates the directional separation of photogenerated carriers while preserving strong redox capability. UV–Vis spectra show broad visible-to-near-infrared absorption dominated by oxygen-deficient W 18 O 49 , whereas a distinct Au LSPR band is not resolved in the ternary composite; therefore, the Au-related plasmonic contribution is discussed cautiously. In-situ DRIFTS identifies *COOH and *CO species associated primarily with the initial CO 2 -to-CO pathway. These results demonstrate improved carrier utilization and surface reaction kinetics in the Au-modified W 18 O 49 /g-C 3 N 4 system.