2D/2D Coupled ZnIn₂S₄/TiO₂Heterojunction and Its Enhanced Photocatalytic Reduction of CO₂

As a typical photocatalytic material, titanium dioxide (TiO2) has been widely applied in environmental remediation and energy conversion due to its excellent chemical stability, non-toxicity and low cost. However, its wide bandgap structure restricts light absorption to ultraviolet wavelengths, and severe recombination of photogenerated electron-hole pairs in bulk materials limits quantum efficiency. Here, a hydrothermal method was used to construct a novel 2D/2D coupled ZnIn2S4 (ZIS)@TiO2 composite material. This heterojunction consists of ultrathin TiO2 nanocages composited with ZIS nanosheets, exhibiting a unique hollow core-shell morphology. ZIS-T20 catalyst with composite 20 mg TiO2 nanocages demonstrates significantly enhanced light absorption across a broad wavelength range of 400-720 nm. Under influence of the built-in electric field, photo-generated electrons cannot migrate from conduction band (CB) of ZIS to that of TiO2, whereas the transfer of holes from valence band (VB) of ZIS to that of TiO2 proceeds unimpededly. This spatial separation effect preserves electrons with high reduction potential in ZIS, overcoming inherent drawback of reduced redox capability in conventional type-I heterojunctions. In photocatalytic CO2 reduction (PCR) reaction, ZIS@TiO2 exhibits improved performance, achieving CO and CH4 production rates of 58.87 and 12.03 μmol·g-1·h-1, respectively, with CO selectivity as high as 83.03%. Compared to individual components, the CO yield is 6.15 and 1.96 times higher than that of pristine ZIS and TiO2, respectively. This work not only provides a new strategy for designing efficient 2D/2D heterojunction photocatalysts, but also offers valuable insights into understanding interfacial charge transfer mechanisms.