Generation Mechanism of the Defects in g-C3N4 Synthesized in N2 Atmosphere and the Method for Improving Photocatalysis Activity

One of the most important methods for modifying semiconductors is defect engineering, but only the right quantity of defects in the right chemical environment can produce desirable results. Heat treatment processes associated with g-C3N4 are occasionally carried out in N-2 atmosphere, however, the catalytic performance of g-C3N4 produced by direct condensation of only nitrogen-rich precursors in N-2 atmosphere is often unsatisfactory. This is typically attributed to the introduction of numerous defects, but the actual relationship between the formation of defects and the N-2 atmosphere is rarely explained, and the resulting quantity of defects is difficult to control. We propose that the melam to melem transition is restricted due to the lack of O-2 during the heat treatment of the nitrogen-rich precursor of g-C3N4 in N-2 atmosphere, which leads to a substantial quantity of defects in the synthesized g-C3N4. To enhance its photocatalytic property, we propose a method to reduce the quantity of defects due to calcinating in N-2 atmosphere by protonating the precursor in a way that increases the polymerization of the product. The test analysis indicated that only a moderate quantity of defects that contribute to electron excitation and enhance the separation efficiency and density of photogenerated carriers were retained, and the hydrogen evolution performance of the prepared catalyst was significantly improved.