Cyano group modified carbon nitride with enhanced photoactivity for selective oxidation of benzylamine

Polymeric graphitic carbon nitride (g-C3N4) is a promising photocatalyst but suffers from the high recombination rate of photogenerated carriers. Many strategies for introducing active “sites”, such as heteroatom doping and defect creation, which can hinder recombination by capturing the separated electrons or holes, have been developed to solve the problem. As a polymeric organic material, it is possible to alter the electron structure and improve the charge separation by introducing organic groups with different electronegativities or conjugation properties to the side chains. Herein, we report a facile and efficient CN group modification strategy using the thermal condensation of the thiocyanuric acid (TA) precursor. The sulfur content in the precursor forms CNS and then transforms to CN. The CN group introduced catalyst exhibits enhanced light absorption and a low carrier recombination rate based on optical and photoelectrical measurements. This is due to the formation of a CN group related midgap state between the bandgap of g-C3N4, according to a density functional theory (DFT) calculation. The CN groups can also loosen the stacking texture of g-C3N4 and result in a thinner layer structure during the post-thermal treatment, which can shorten the distance of photogenerated carrier transfer from the bulk to the surface. The CN group introduced photocatalyst is efficient for the selective oxidation of benzylamine to imine, even under green light irradiation. This result demonstrates that the introduction of an electron rich conjugation group such as CN into the edge chain of polymeric carbon nitride is efficient for better photoactivity.