Rich Sulfur Vacancies and Reduced Schottky Barrier Height Synergistically Enable Au/ZnIn2S4 with Enhanced Photocatalytic CO2 Reduction into CO

Abstract

Constructing the plasmonic metal/semiconductor heterostructure with a suitable Schottky barrier height (SBH) and the sufficiently reliable active sites is of importance to achieve highly efficient and selective photocatalytic CO₂ reduction into hydrocarbon fuels. Herein, we report Au/sulfur vacancy-rich ZnIn₂S₄ (Au/V_SR-ZIS) hierarchical photocatalysts, fabricated via in situ photodepositing Au nanoparticles (NPs) onto the nanosheet self-assembled ZnIn₂S₄ (ZIS) micrometer flowers (MFs) with rich sulfur vacancies (V_S). Density functional theory (DFT) calculations confirm that for the Au/V_SR-ZIS system, the Au NPs serve as the reaction sites for H₂O oxidation, and the V_SR-ZIS MFs serve as those for CO₂ reduction. The rich V_S in the Au/V_SR-ZIS hybrid can reduce its SBH so as to boost more hot electrons in the Au NPs across its Schottky barrier and then inject into the conduction band (CB) of the V_SR-ZIS MFs. In addition, V_S can also act as the electron sink to trap the photogenerated electrons, retarding the recombination of photogenerated carriers. The two merits effectively enhance the photogenerated electron density in the surface of V_SR-ZIS MFs, availing CO₂ photoreduction. In addition, the introduction of rich V_S in the Au/V_SR-ZIS hybrid can offer more active sites, benefiting the CO₂ adsorption and accelerating the desorption of CO* from the surface of the photocatalyst. Therefore, under visible light illumination with no sacrificial reagent, the optimum photocatalyst (Au/V_SR-ZIS-0.4) presents the enhanced and selective CO₂ photoreduction into CO (8.15 μmol g^–1h^–1 and near 100%), which are superior to those of most of ZIS-based and plasmon-based photocatalysts. The photocatalytic activity is about 40.0-fold as high as that of the Vs-poor-ZIS (V_SP-ZIS) MFs. This work contributes a viable strategy for designing highly efficient plasmonic photocatalysts by using the synergism of the anion vacancies and the optimized SBH induced by them.