Tunable Type-II BiVO4/ g - C3 N4 Nanoheterostructures for Photocatalysis Applications

Bismuth vanadate-graphitic carbon nitride (BiVO4/g-C3N4) heterostructures combining the advantages of bismuth vanadate and graphitic carbon nitride have recently emerged as a promising material system for photocatalytic applications. Further performance improvement will require in-depth understanding and fine tuning the near-edge electronic properties of these heterostructures. We investigate the electronic properties, in particular, the band-edge states, that control the optical and transport properties of BiVO4/g-C3N4 nanoheterostructures using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional approach. Our results demonstrate that BiVO4/g-C3N4 heterostructures have a desired type-II band alignment, which may greatly facilitate rapid separation of photogenerated carriers. We find that the BiVO4 subsystem is responsible for the robust and strong optical absorption observed experimentally. Our calculated absorption edge of about 2.5 eV agrees remarkably well with the experimental value of 2.45 eV. We also investigate the effect of an external electric field on the band-edge states, band alignment, and the optical and fundamental band gaps of the BiVO4/g-C3N4 heterostructures. The band-edge states of the BiVO4 and g-C3N4 subsystems respond very differently to the applied electric field, resulting in electric field-tunable band offsets and band gap of the BiVO4/g-C3N4 heterostructures. The contrasting response of the fundamental and optical gaps to an electric field suggests an alternative avenue for future experimental optimization of the optical absorption and carrier separation dynamics of these heterostructures for photoelectrochemical catalysis applications.