Insight into the effective electrocatalytic sulfide removal from aqueous solutions using surface oxidized stainless-steel anode and its desulfurization mechanism

The electrochemical oxidation removal method is effective for hydrogen sulfide (H2S) from wastewater. In this study, a surface corrosion treatment was used to achieve the Ni content regulating in the oxide film of the AISI 304 stainless steel (SS) surface. This made the low-cost SS substrate into a highly efficient electrochemical sulfide removal anode. The X-ray photoelectron spectroscopy (XPS) and linear sweeping voltammetry (LSV) results indicated the higher Ni content in the oxide film of surface-oxidized stainless steel (SOSS) attributed to the higher sulfide removal potential. Sulfide removal experiments results further demonstrated it, and the results showed that SS-150 (with 150 s anodic pretreatment) anodes reached the highest Ni content (about 69 %) and resulted in the best sulfide removal efficiency, achieving about 97 % within 48 h, which was increased by about 20 % compared to the untreated SS. Moreover, this study also demonstrated a strategy for in situ recovery of deposited sulfur on the anodes by cathodic recovery under −0.38 V vs. RHE to alleviate the electrode sulfur loaded problem which was the common issue limiting the sulfide removal process. Besides, the mechanism analysis by density functional theory (DFT) revealed that NiOOH was the main active site for SS-150 to obtain the faster sulfide removal rate, and the Mulliken charge population further illustrated the oxidation reaction of sulfide. The process shows the potential of the modified SS for continuous removal of hydrogen sulfide as sulfur from wastewater and recovery of the loaded sulfur through periodic shifting between anode sulfide oxidization and cathode-loaded sulfur restoration.