Functional group boosting triazine ring-opening for low-temperature synthesis of heptazine-based graphitic carbon nitride†

Abstract

Graphitic carbon nitride (g-CN) is a promising semiconductor material with diverse applications. It is typically synthesized by thermally polymerizing nitrogen–carbon precursors, like melamine or urea, at elevated temperatures (typically ∼550 °C). However, the high energy consumption associated with these methods poses challenges for scalable and sustainable production. Here we develop a functional group engineering to boost the thermal polymerization reaction to produce g-CN at low temperature. When the functional groups phenyl (–Ph), methyl (–CH₃), and chlorine (–Cl) substitute the amino (–NH₂) group in melamine, the electron density in the triazine ring decreases progressively due to the electron-donating/withdrawing effect. Therefore, the bond energy of –CN– and the stability of the triazine unit would be weakened, consequently boosting the ring-opening reaction. Multiple structural characterization processes confirm that as the withdrawing ability of the functional group increases, the synthesis temperatures of g-CN reduce from about 550 to 300 °C. Our work provides new insights and practical strategies for the sustainable, low-energy synthesis of g-CN, advancing its potential for broader applications.