Polarization Reorientation of Carbon Nitride Induced by a Local Bridge Donor for Boosting Photocatalytic H2 Evolution Integrated with Selective Amine Oxidation

Abstract

Polymeric carbon nitride (PCN) has attracted much attention in the field of photocatalysis, but the use of PCN is often confined to internal structures with highly symmetrical heptazine units bridged by N atoms. Accurate tuning of the positions of heteronuclear atoms is a meaningful strategy but remains a big challenge. Herein, a catalyst with P═N bonds accurately embedded among the heptazine units was prepared using a straightforward polymerization method. According to density functional theory simulation and experimental data, the embedded P═N chains act as donor units that cause a profound redistribution of the symmetric electron cloud density of heptazine, which significantly promotes local charge polarization and leads to a strong built-in electric field. The consequence is enhanced exciton dissociation, charge separation, and surface activation. In the photocatalytic oxidation of benzylamine over the optimized PCN under visible light irradiation without the use of a solvent and co-catalyst, the hydrogen production rate is 388 μmol·g–1·h–1 and the selectivity to N-benzylidenebenzylamine is >99%. In this paper, we propose a tractable strategy to precisely tune the position of heteroatoms, providing an efficient catalyst for hydrogen production together with the simultaneous generation of value-added imines.