Constructing carbon-defect-rich g-C₃N₄/In₂S₃ 2D vertically stacked Z-scheme heterojunction for ultrafast photocatalytic Cr(VI) reduction

2D/2D face-to-face heterojunctions in photocatalyst could promote the migration and separation of carriers to improve photocatalytic properties, however, the accumulation of nanosheets leads to carrier transport needs to pass through a long and winding channel. To further solve this matter, we altered parallel stacking of 2D materials to vertical stacking model, and constructed g-C₃N₄/In₂S₃ 2D vertically stacked Z-scheme heterojunction with carbon defects for accelerating the separation and migration of carriers. The optimized 10CNIS photocatalyst exhibits an incredibly rapid photocatalytic conversion of Cr(VI) to Cr(III) under optical light within only 2 min with rate constant of k = 2.054 min⁻¹, nearly 128.4 and 5.1 times faster than pristine g-C₃N₄ (0.016 min⁻¹) and In₂S₃ (0.405 min⁻¹). Through mechanism investigation, we demonstrated that the 2D vertically stacked Z-scheme structure could effectively provide more diffusion paths for carriers and simultaneously maintain higher redox ability, which greatly promotes the mobility and reducibility of charge, improves the separation of photoexcited electron-hole pairs. In addition, carbon defects in-situ constructed in the g-C₃N₄ could partly diminish the surface inertness of g-C₃N₄ and enhance its interaction with desired reactants. This study offers an imaginative inspiration for developing special 2D vertically stacked Z-scheme photocatalysts to handle the environmental pollution issues.