Constructing multifunctional novel noble-metal free NiS/ZnS/g-C₃N₄ ternary nanocomposites for highly active superior photocatalytic water splitting

Ultrasound-assisted wet-impregnation approach and cation-exchange hydrothermal method are employed effectively to develop the ternary nanocomposites NiS/ZnS/g-C₃N₄ (NZ-CN) with promising photocatalytic hydrogen (H₂) generation activity. Several analytical techniques are utilized to characterize the as-synthesized NiS/ZnS/g-C₃N₄ nanocomposites to study their physical and chemical characteristics. The H₂ production activity of the synthesized photocatalysts was tested using a 250 W halogen lamp with Na₂S (0.25 M) and Na₂SO₃ (0.35 M) as sacrificial reagents. The optimized NZ-CN7.5% (3% NiS/ZnS/7.5% g-C₃N₄) catalyst displayed an exceptional H₂ generation rate of 8624 μmol h⁻¹ g⁻¹, exceeding both, pristine g-C₃N₄ (by 22.1 times) and 3% NiS/ZnS (by 3 times). This represents the highest reported rate of H₂ evolution for a graphitic carbon nitride (g-C₃N₄) based ternary nanocomposite under simulated solar radiation. By reusing the used NZ-CN7.5% (3% NiS/ZnS/7.5% g-C₃N₄) photocatalyst in four consecutive runs, the stability of the catalyst was investigated, and their individual activity in the H₂ production activity was assessed. This study provides valuable insights for designing efficient noble metal-free g–C₃N₄–based photocatalysts, which can significantly contribute to the transition to solar-driven hydrogen generation. Further, we proposed a plausible mechanism for the photocatalytic H₂ generation process over the NiS/ZnS/g-C₃N₄ photocatalyst.