Boosting the Photoreactivity of g-C3N4 towards CO2 Reduction by Polymerization of Dicyandiamide in Ammonium Chloride

As a typical organic semiconductor photocatalyst, graphitic carbon nitride (g-C3N4) suffers from low photocatalytic activity. In this paper, g-C3N4 was prepared by polymerization of dicyandiamide (C2H4N4) in the presence of ammonium chloride (NH4Cl). It was found that the addition of ammonium chloride can greatly improve the photocatalytic activity of g-C3N4 towards CO2 reduction. The optimal photocatalyst (CN-Cl 20) exhibited a CO2-to-CO conversion activity of 50.6 μmolg−1h−1, which is 3.1 times that of pristine bulk g-C3N4 (BCN) that was prepared in the absence of any ammonium chloride. The enhanced photoactivity of g-C3N4 was attributed to the combined effects of chloride modification and an enlarged specific surface area. Chloride modification of g-C3N4 can not only reduce the bandgap, but also causes a negatively shifted conduction band (CB) potential level, while ammonia (NH3) gas from the decomposition of NH4Cl can act as a gas template to exfoliate layered structure g-C3N4, improving the specific surface from 6.8 to 21.3 m2g−1. This study provides new ideas for the synthesis of highly efficient g-C3N4-based photocatalytic materials for CO2 conversion and utilization.