Unlocking the Exceptional Activity of CuS in Fenton-Like Reactions via a Novel Hydroxide–Sulfur Interaction

Promoters have been explored to improve Fenton-like reactions for wastewater treatment, yet they are often costly and may cause secondary pollution. This study demonstrates that alkali (OH–), as an inexpensive and environmentally friendly chemical, acts as an efficient promoter for copper sulfide (CuS) by inducing polarization of the disulfide bonds in CuS. OH– substantially enhanced the generation of hydroxyl and sulfate radicals in the CuS/peroxymonosulfate (PMS) system, achieving a >100-fold increase in the apparent degradation rate of sulfamethoxazole (SMX). With OH– assistance, a CuS-packed continuous-flow reactor demonstrated long-term stability (≥800 h), sustaining >95% SMX removal, <1% residual PMS, <0.03 mg/L Cu2+ leaching. Final effluent pH remained stable at 6–9, meeting all applicable discharge standards. Furthermore, the OH–/CuS/PMS system significantly reduced the toxicity of actual wastewater. Density functional theory calculations revealed that the interaction between OH– and disulfide bonds in CuS enhanced the electron spin density and improved the 3d orbital energy level of CuS, promoting electron transfer from CuS to PMS. This work presents a cost-effective Fenton-like system that achieves robust pollutant degradation while ensuring exceptionally low metal dissolution and a consistently discharge-compliant effluent pH (6–9), collectively underscoring its viability for sustainable wastewater remediation.