Cooperative photocatalytic H2 liberation and benzyl alcohol C–C coupling reactions on Zn2In2S5 embracing Zn/In dual vacancies†

Photocatalytic benzyl alcohol (BA) conversion is a promising approach for coproducing H₂ and value-added chemicals but is subject to low efficiency. Here, a dual defect engineering strategy has been applied to Zn₂In₂S₅, i.e. by constructing both Zn and In vacancies (V_Zn/V_In), which enables efficient BA conversion to H₂ and valuable carbon–carbon (C–C) coupling compounds. Compared with previous strategies using V_Zn defects alone, our dual-defect strategy is more effective at separating photocarriers and thus can provide more usable photocarriers for BA conversion. With the optimized dual-defect content, Zn₂In₂S₅ can deliver an apparent quantum yield (AQY) as high as 8.3% at 420 ± 20 nm for the generation of the C–C coupling compounds. DFT calculations reveal that the V_Zn/V_In dual defects can (1) endow the photogenerated electrons with high mobility and high reducing power, (2) enlarge the energetically downhill step for the formation of ketyl radicals, and (3) lower the energy barriers for the coupling of ketyl radicals. These findings not only expand the toolbox for the design and modification of semiconductor photocatalysts but also provide an in-depth understanding of the role of various defects in photocatalytic BA conversion.