Synthesis of hierarchical SnS₂@SnO₂ heterojunction on carbon-fiber cloth for efficient removal of Cr(VI) ions from aqueous solution

A novel three-dimensional (3D) carbon fiber (CF) cloth@SnS₂@SnO₂ heterostructure photocatalyst has been synthesized via a facile two-step method, which involves a solvothermal preparation of SnS₂ nanosheets (about 20 nm in thickness) on the surface of CF cloth substrate and a subsequent in situ growth of SnO₂ nanoparticles (20 ~ 50 nm in diameter) on the surface of SnS₂ nanosheets by thermal oxidation annealing in air. Compared with CF cloth@SnS₂ and CF cloth@SnO₂, CF cloth@SnS₂@SnO₂ exhibits superior photocatalytic activity and excellent stability in the reduction of toxic Cr(VI) ions in aqueous solution. The reduction constant of Cr(VI) ions for CF cloth@SnS₂@SnO₂ is 22 times and 53 times that of CF cloth@SnS₂ and CF cloth@SnO₂, respectively. We speculate that the improved photocatalytic activity of CF cloth@SnS₂@SnO₂ is mainly ascribed to the formation of type-II heterojunction between SnS₂ and SnO₂ as well as the excellent electrical conductivity of CF cloth, which promotes the separation and transport of photogenerated carriers. In addition, the hierarchical 3D nanostructure with abundant reactive sites and the enhanced absorption of Cr(VI) ions due to the formation of oxygen vacancies on SnO₂ nanoparticles also contributed to the improved photocatalytic activity for CF cloth@SnS₂@SnO₂. Therefore, CF cloth@SnS₂/SnO₂ heterojunction can be used as an efficient, stable and recyclable photocatalyst, which has great potential in the practical application of wastewater treatment.