Theoretical design and experimental study a novel direct Z-scheme V2O5/C3N5 heterojunction for efficient photocatalytic hydrogen production

The key to construct an efficient direct Z-scheme heterojunction lies in the selection of two semiconductors with matching Fermi energy levels, visible light response capability and the elaborately designed interface. Herein, a research method that theoretical calculation first and then experimental study was employed to develop an efficient direct Z-scheme V2O5/C3N5 photocatalyst for hydrogen production. First, the theoretical calculations on the V2O5 (110)/C3N5 (001) heterojunction suggested the large interface binding energy between these two components, their visible-light absorption properties and matching Fermi energy levels, and the charge difference density of V2O5/C3N5 allowing the migration path of photogenerated carriers in composite structure, which satisfies the requirements for constructing a direct Z-scheme. Then, the V2O5/C3N5 heterojunction was experimentally constructed by calcining the mixture of 3-amino-1,2,4-triazole and ammonium metavanadate, which Z-scheme charge transfer path was further verified by free radical trapping and in situ irradiated XPS analyses. We also found that N–O bonding was formed between C3N5 and V2O5, which could provide a favorable interface for facilitating the charge transfer within the heterojunction. The optimal V2O5/C3N5-3.7 heterojunction exhibited a H2 yield of 329.9 μmol/h under the visible light irradiation, 19.8 times that of single C3N5, and showed an apparent quantum efficiency of 7.21% at 420 nm. The high charge separation of the V2O5/C3N5 heterojunction is revealed to be mainly responsible for the enhancement in its photocatalytic activity. This work sheds light on the research method that consists of theoretical design first and then experimental study for constructing high-efficiency direct Z-scheme heterojunctions.