Near-Infrared Photothermal Effect Boosting Photocatalytic CO2 Reduction by Black Ga-Doped Carbon Nitride

Efficient use of solar energy for photocatalytic reduction of CO₂ into CO, especially in the visible and NIR ranges, remains challenging. Herein, we report a unique gallium-doped carbon nitride (DFCN-Ga) with effective photothermal conversion. The dandelion flower-like morphology with a black appearance was successfully modified using a template-free solvothermal method. The catalyst was characterized by various methods, which showed that it had a cluster structure with overlapping petal-like sheets, a large specific surface area (105.6 m²/g), and a wide light absorption range (300–1500 nm, as determined by UV–vis DRS spectra). Different illumination conditions were set up to evaluate DFCN-Ga’s photothermal-catalytic activity for CO₂ reduction. Under full-spectrum light, without external heating, the yield of CO (98.2 μmol·h^–1·g^–1) with DFCN-Ga as the catalyst under simulated solar light was 16.1 times higher than that achieved with graphitic carbon nitride (GCN). The results showed that infrared light effectively enhanced the catalysts’ photocatalytic activity. To investigate the reaction pathway, the density functional theoretical method was used to study the role of structural changes in the photocatalytic reaction. It was found that DFCN-Ga could effectively separate HOMO and LUMO orbitals, lower the free energy of *COOH formation, and significantly increase the rate of CO₂ to CO photocatalytic reduction. Our research provides a unique approach to the synthesis and application of high-efficiency catalysts with full-spectrum activity.