The interfacial charge transfer in triphenylphosphine-based COF/PCN heterojunctions and its promotional effects on photocatalytic hydrogen evolution

In this study, the novel triphenylphosphine-based covalent organic frameworks (P–COF-1) were firstly introduced into polymeric carbon nitride (PCN) to fabricate P–COF-1/PCN heterojunctions via intermolecular π-π interaction. The photocatalytic H2 production rate over the 9% P–COF-1/PCN heterojunctions is ca. 12 times as much as that of pure PCN. The photoelectrochemical measurements and theoretical calculation results show that due to the well-matched band structure between P–COF-1 and PCN, the photo-generated electrons tend to migrate from P–COF-1 into the conduction band of PCN through the interface of heterostructures. In addition to the π→π∗ electron transition of conjugated tri-s-triazine units in the 9% P–COF-1/PCN with band gap energy of 2.53 eV, the lone pair electrons of P transition to the π∗ orbitals of P–COF-1 (n→π∗) with lower band gap energy of 1.82 eV results in the effective separation of photo-generated carriers and more visible light absorption, and thus enhanced the photocatalytic hydrogen evolution.