Sub-Band Assisted Z-Scheme for Effective Non-Sacrificial H2O2 Photosynthesis.

ABSTRACT

Photosynthesis of H2O2 from earth-abundant O2 and H2O molecules offers an eco-friendly route for solar-to-chemical conversion. The persistent challenge is to tune the photo-/thermo- dynamics of a photocatalyst toward efficient electron-hole separation while maintaining an effective driving force for charge transfer. Such a case is achieved here by way of a synergetic strategy of sub-band-assisted Z-Scheme for effective H2O2 photosynthesis via direct O2 reduction and H2O oxidation without a sacrificial agent. The optimized SnS2/g-C3N4 heterojunction shows a high reactivity of 623.0 µmol g-1 h-1 for H2O2 production under visible-light irradiation (λ > 400 nm) in pure water, ≈6 times higher than pristine g-C3N4 (100.5 µmol g-1 h-1). Photodynamic characterizations and theoretical calculations reveal that the enhanced photoactivity is due to a markedly promoted lifetime of trapped active electrons (204.9 ps in the sub-band and >2.0 ns in a shallow band) and highly improved O2 activation, as a result of the formation of a suitable sub-band and catalytic sites along with a low Gibbs-free energy for charge transfer. Moreover, the Z-Scheme heterojunction creates and sustains a large driving force for O2 and H2O conversion to high value-added H2O2.