Photocatalytic conversion of H₂S using NiS₂/CdS_0.90Se_0.10 Schottky heterojunction in NaOH/Na₂SO₃ solution

Photocatalytic conversion of toxic hydrogen sulfide (H₂S) waste gas into high-purity hydrogen (H₂) and value-added sulfur-containing chemicals has emerged as a transformative technological solution for enhancing sustainability in the coal chemical and petrochemical sectors. In this study, a selenium (Se) doping strategy was employed to synthesize CdS_1-xSe_x solid solution photocatalysts, enabling precise band-gap modulation to alleviate rapid charge recombination and photo-corrosion of CdS. At an optimized Se content of x = 0.10, the resulting material exhibits a more negative conduction band minimum, thereby enhancing the thermodynamic driving force for H₂ evolution. Subsequently, a Schottky junction was constructed by depositing NiS₂ cocatalyst onto the surface of CdS_0.90Se_0.10 (CSS). The 2 wt% NiS₂/CSS composite delivered a H₂ evolution rate of 3.5 mmol g^-1 h^-1 in an H₂S-saturated solution (0.2 M NaOH, 0.6 M Na₂SO₃), corresponding to a 2.9-fold enhancement over pristine CSS. Electrochemical characterization showed that incorporation of the NiS₂ cocatalyst reduced the charge-transfer resistance and H₂ evolution overpotential, and increased the electrochemically active surface area. Fourier transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and thiosulfate (S₂O₃^2-) titration confirmed the concurrent conversion of H₂S to S₂O₃^2-. Moreover, the alkaline reaction medium contributed to improved catalyst stability. This synergistic strategy addresses the twin challenges of chalcogenide photocorrosion and decomposition of waste H₂S, thereby providing experimental evidence for the valorization of sulfur-containing wastes and H₂ production.