Achieving highly efficient and selective CO2 photoreduction to CO over g-C3N4 via micro-environment optimization mediated by HZSM-5 zeolite integration

The most promising and environmentally friendly strategy to address the greenhouse effect is to utilize renewable solar energy and semiconductor photocatalytic technology to convert excessive CO₂ into valuable chemicals. However, the unsatisfactory photoreduction activity and product selectivity of pristine semiconductor remain significant barriers to their large-scale industrial application. In this study, graphitic carbon nitride (g-C 3 N 4 ) was selected as a model photocatalyst, and HZSM-5 zeolite with a high Si/Al ratio of 500 was employed to synthesize g-C 3 N 4 /HZSM-5 composite via a simple thermal polymerization method. The incorporation of HZSM-5 zeolite, characterized by its rich pore structure, significantly increased the composite's specific surface area, thereby reducing the transportation distance of photoexcited charge carriers and enhancing photoelectric conversion efficiency. The pore structure of HZSM-5 zeolite facilitated the enrichment of CO 2 , increasing the local reactant concentration. Additionally, the specific pore micro-environment exhibited a lower adsorption strength for the reduction product (CO), preventing its further conversion into undesired by-products. Furthermore, the weak acidity of the micro-environment contributed to the stabilization of intermediates, such as -HCO 3 and -COOH, promoting specific reaction pathways. As a result, the g-C 3 N 4 /HZSM-5 composite achieved high CO 2 photoreduction activity and CO selectivity (>95 %). This work highlights the potential of designing composite photocatalysts with tailored micro-environments for efficient and selective CO 2 photoreduction.