Photocatalytic conversion of H2S using NiS2/CdS0.90Se0.10 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 CdS1-xSex 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 CdS0.90Se0.10 (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 (S2O32-) titration confirmed the concurrent conversion of H2S to S2O32-. 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.