Photocatalytic conversion of H2S using NiS2/CdS0.90Se0.10 Schottky heterojunction in NaOH/Na2SO3 solution

Treating H 2 S in a NaOH/Na 2 SO 3 solution simultaneously transforms it into H 2 /Na 2 S 2 O 3 . • Precise control of the Se/S atomic ratio in CdS 1− x Se x solid solutions enables continuous bandgap tuning. • The construction of a NiS 2 /CdS 0.90 Se 0.10 Schottky heterojunction enhances interfacial charge separation efficiency. • Investigation of the compositional evolution of CdS 0.90 Se 0.10 under varying alkaline conditions and its intrinsic mechanism underlying enhanced hydrogen evolution activity. Photocatalytic conversion of toxic hydrogen sulfide (H 2 S) waste gas into high-purity hydrogen (H 2 ) 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- x Se 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 H 2 evolution. Subsequently, a Schottky junction was constructed by depositing NiS 2 cocatalyst onto the surface of CdS 0.90 Se 0.10 (CSS). The 2 wt % NiS 2 /CSS composite delivered a H 2 evolution rate of 3.5 mmol g −1  h −1 in an H 2 S-saturated solution (0.2 M NaOH, 0.6 M Na 2 SO 3 ), corresponding to a 2.9-fold enhancement over pristine CSS. Electrochemical characterization showed that incorporation of the NiS 2 cocatalyst reduced the charge-transfer resistance and H 2 evolution overpotential, and increased the electrochemically active surface area. Fourier transform infrared spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, and thiosulfate (S 2 O 3 2− ) titration confirmed the concurrent conversion of H 2 S to S 2 O 3 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 H 2 S, thereby providing experimental evidence for the valorization of sulfur-containing wastes and H 2 production. This study reports a CdS 1- x Se x /NiS 2 photocatalytic system that achieves efficient, alkaline-mediated conversion of toxic H 2 S into high-purity H 2 and S 2 O 3 2− , while simultaneously suppressing photocorrosion and enhancing charge separation. It establishes a robust, sulfur-centered strategy for H 2 S valorization. Download: Download high-res image (310KB) Download: Download full-size image