Ti³⁺ Defective SnS₂/TiO₂ Heterojunction Photocatalyst for Visible-Light Driven Reduction of CO₂ to CO with High Selectivity

In recent years, defective TiO₂-based composite nanomaterials have received much attention in the field of photocatalysis. In this work, TiB₂ was used as a precursor to successfully prepare Ti³⁺ defective TiO₂ (TiO₂-B) with a truncated bipyramidal structure by a one-step method. Then, the SnS₂ nanosheets were assembled onto the as-prepared TiO₂-B through simple hydrothermal reaction. TiO₂-B exhibits strong visible light absorption properties, but the recombination rate of the photo-generated electron-hole pair was high and does not exhibit ideal photocatalytic performance. Upon introducing SnS₂, the heterojunction catalyst SnS₂-Ti³⁺ defective TiO₂ (SnS₂/TiO₂-B) not only possesses the strong light absorption from UV to visible light region, the lowest photo-generated charge recombination rate but also achieves a more negative conduction band potential than the reduction potential of CO₂ to CO, and thereby, exhibits the significantly enhanced selectivity and yield of CO in photocatalytic CO₂ reduction. Notably, SnS₂/TiO₂-B produces CO at a rate of 58 µmol·h⁻¹·g⁻¹ with CO selectivity of 96.3% under visible light irradiation, which is 2 and 19 times greater than those of alone TiO₂-B and SnS₂, respectively. Finally, a plausible photocatalytic mechanism on SnS₂/TiO₂-B was proposed that the electron transfer between TiO₂ and SnS₂ follows the Z-scheme mode. Our results present an effective way to gain highly efficient TiO₂ based photocatalysts for CO₂ reduction by combining different modification methods of TiO₂ and make full use of the synergistic effects.