Electrostatic potential of the incorporated asymmetry molecules induced high charge separation efficiency of the modified carbon nitride copolymers

Although the carbon nitrides copolymers (CNs) exhibit enhanced photocatalytic performance, the essential reason remains unclear. Systematic research on incorporated molecules with structure similarity but different natures helps gain a fundamental understanding of CNs photocatalyzed reactions. A series of dihydroxyl-N-heterobenzene with a different number of N atoms and at different positions of the six-member ring are selected for constructing CNs. Structural identifications demonstrate N-heterobenzene links with heptazine of CN networks at the hydroxyl sites in the synthesized CNs. The theoretical calculation reveals that the electrostatic potential (ESP) of asymmetry pyridine strongly induces the HOMO and LUMO separation, located at different heptazine units. This is significantly different from the traditional heterojunction or D-A system. A kinetics study of CNs/triethanolamine system for photocatalysis was carried out with photovoltage spectra of CNs series. The linear- relationship between extraction charge and H2 generation rate suggests a Volmer-Heyrovsky mechanism which is commonly acknowledged for electrocatalysis but barely mentioned in photocatalysis. [Display omitted] •Modified polymeric carbon nitrides with clear chemical structures are synthesized and characterized.•High charge separation efficiency is dominated contributor for photocatalytic activity enhancement.•The electrostatic potential of the incorporated molecules induces spatial charge separation.•The photocatalytic H2 production process follows the Volmer-Heyrovsky Mechanism for the carbon nitride/triethanolamine system.