Abstract: This study aims to construct a composite photocatalytic system with both strong reductive electron retention capability and efficient charge separation properties for the highly selective conversion of carbon dioxide to methanol. Graphitic carbon nitride was prepared via thermal polymerization, and molybdenum diselenide was in-situ loaded through a one-step solvothermal method to fabricate composites with different loading ratios. Combined with structural characterization, photoelectric property measurements and energy band analyses, the interfacial charge transfer mechanism and reaction pathways were systematically investigated. The results showed that the composite with 70 wt% molybdenum diselenide exhibited the optimal performance, with a gaseous methanol yield of 14.433 μmol g-1 h-1 and a selectivity of 69.3%, and the total yield reached 76.248 mmol g-1 h-1, approximately 15 times higher than that of pure graphitic carbon nitride. Mechanistic analysis confirmed that the system retained strong reductive electrons in the conduction band of molybdenum diselenide via a direct Z-scheme heterojunction, and promoted the multi-electron proton-coupled reaction process. This work provides a design strategy combining interface engineering and energy band modulation for highly selective photocatalytic CO2 reduction to methanol, which is of great theoretical significance and application value for the optimization of artificial photosynthesis systems.

Key words: Photocatalysis, Carbon Dioxide Reduction, Molybdenum Selenide, Carbon Nitride