A highly efficient Z-scheme B-doped g-C3N4/SnS2 photocatalyst for CO2 reduction reaction: a computational study

Abstract

A Z-scheme heterostructure is a kind of highly efficient photocatalyst that can not only reduce the forbidden band width of the semiconductor but also promote the redox reaction in the photocatalytic system. Herein, calculations on the work function and charge density difference by density functional theory (DFT) methods prove that g-C₃N₄/SnS₂ and B-doped g-C₃N₄/SnS₂ are Z-scheme heterostructures. Compared to g-C₃N₄, the Z-scheme heterostructures show narrower band gaps, and red-shifted and stronger light absorption with remarkably improved photocatalytic activity. The reaction free energy for each step of the CO₂ reduction process was calculated to further evaluate the photocatalytic activity of g-C₃N₄/SnS₂ and B-doped g-C₃N₄/SnS₂. The products of CO₂RR catalyzed by g-C₃N₄/SnS₂ are CH₃OH and CH₄, which are in good agreement with experiments, and the rate-determining step is CO₂ → COOH* with a ΔG of 1.10 eV. For B-doped g-C₃N₄/SnS₂, the optimal path is CO₂ → COOH* → CO* → HCO* → CHOH* → CH* → CH₂* → CH₃* → CH₄, and the rate-determining step is CH₂* → CH₃* with a ΔG of 0.40 eV. The results show that the CO₂ reduction activity of B-doped g-C₃N₄/SnS₂ is better than that of g-C₃N₄/SnS₂. Therefore, the Z-scheme B-doped g-C₃N₄/SnS₂ heterostructure is predicted to be a promising catalyst for CO₂ reduction to CH₄.