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 N₂ atmosphere, however, the catalytic performance of g-C₃N₄ produced by direct condensation of only nitrogen-rich precursors in N₂ 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 N₂ 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 O₂ during the heat treatment of the nitrogen-rich precursor of g-C₃N₄ in N₂ 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 N₂ 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.