CO₂ Photoreduction Improvement by Carbon Nitride Utilizing the Synergism of Na Ion and Cyano Defects

Conversion of CO₂ to high value products was considered as a focused issue towards carbon neutrality. Photocatalysis held the potential to realize the target, and graphitic carbon nitride (g-C₃N₄) was a competitive candidate. The photocatalytic efficiency of g-C₃N₄ limited by the weak adsorption of CO₂ and easy recombination of charge carriers. Herein, Na ion and cyano defects was induced into g-C₃N₄ simultaneously using NaHSO₃ as alkali molten salt to work out these obstacles. The optimized photocatalyst 3 Na-CN (the weight of NaHSO₃ was 1.5 g) exhibited the highest CO yield (21.5 μmol g^-1 h^-1), which was 5 times than that of pristine g-C₃N₄ (4.29 μmol g^-1 h^-1). By means of experiments and characterization, 3 Na-CN displayed better performance in both light utilization and charge separation, which was reflected by the improved photocurrent response, decreased electrochemical impedance, markedly diminished fluorescence intensity, and shortened fluorescence lifetime. This result could be ascribed to the facilitation of electron-hole separation induced by cyano defects, as well as the enhancement in CO₂ adsorption and activation mediated by the Na ion. This work offers a new perspective on dual modulation of graphitic carbon nitride and paves the way for the design of CO₂ reduction photocatalyst.