Effect of thermal program on structure–activity relationship of g-C3N4 prepared by urea pyrolysis and its application for controllable production of g-C3N4

Highlights: • Obtaining g-C₃N₄ with specific property purposedly by adjusting the heating process. • Elucidating the structure-activity relationship of g-C₃N₄ to achieve rational production. • Determining the crucial effect of heating rate on structure and performance of g-C₃N_4. • Realizing the performance enhancement of g-C₃N₄ as photocatalyst, adsorbent and lubricant. • Providing a referable strategy for customized production of g-C₃N₄ as mass product in industry. Graphitic carbon nitride (g-C₃N₄) can be easily prepared by urea pyrolysis; however, its properties are greatly affected by the thermal program used in the pyrolysis process, especially the heating rate, owing to the complexity of the pyrolysis reaction. In this work, the effects of three main parameters—pyrolysis temperature, heating time, and heating rate—on the structure and performance of g-C₃N₄ are systematically investigated, and the results are used to guide the controllable production of g-C₃N₄ to obtain suitable properties for application as a photocatalyst, adsorbent, or lubricant. The results show that urea pyrolysis follows the same reaction path regardless of the parameters. However, the polymerization reaction rate significantly affects the structure, morphology, and surface composition of g-C₃N₄, indicating a clear structure–activity relationship. Rapid heating produces g-C₃N₄ with loose thin layers, a larger surface area, more amino defects, and more conjugated structure; these characteristics promote adsorption and photocatalysis. Slow heating produces g-C₃N₄ with a higher polymerization degree, more complete layer structure, and tighter layer spacing, which is suitable for lubrication. A high pyrolysis temperature and long heating period further enhance the performance of g-C₃N₄. This study provides a reference for large-scale controllable production of g-C₃N₄ by urea pyrolysis.