Degradation of Tetracycline in Wastewater by Persulfate Activated by Sulfidated Nanometer Zero-valent Iron

Sulfidated zero-valent iron (S–nZVI) has been extensively utilized in wastewater treatment in recent years due to its superior electron transfer efficiency and selectivity. Integrating S–nZVI with advanced oxidation technology enhances the catalytic performance of the material, leading to efficient pollutant degradation. This study employs thiourea as the sulfur source to prepare highly active S–nZVI and constructs an S–nZVI-activated per-disulfide PDS oxidation system to achieve efficient tetracycline degradation. The composition and surface morphology of S–nZVI is characterized using scanning electron microscopy (SEM), X–ray diffraction (XRD), specific surface area (BET), and X–ray photoelectron spectroscopy (XPS). The effects of the molar ratio (S/Fe), vulcanization time, S–nZVI dosage, PDS concentration, initial pH of the solution, and coexisting ions on tetracycline (TC) degradation are examined. Active species quenching experiments and electron paramagnetic resonance (EPR) experiments explore TC degradation by both free radical and non-radical active species, while liquid chromatography-mass spectrometry (LC–MS) analyzes the potential pathways of tetracycline degradation. Test results indicated that vulcanization modification increases the specific surface area of nano-zero-valent iron (nZVI), and iron (Fe) and sulfur (S) are uniformly distributed on the surface of the material. The impact of S/Fe on TC degradation is minimal, and the degradation rate correlates positively with the dosage of S–nZVI and PDS concentration but shows a decreasing trend with prolonged vulcanization time. The S–nZVI/PDS system exhibits an enhanced TC degradation effect across a wide pH range (pH=5～9). The presence of different anions in the reaction solution variably inhibits the degradation rate of TC, with HCO−3 having the most significant effect. At a S/Fe ratio of 0.028, a vulcanization time of 2 h, an S–nZVI dosage of 1 g/L, a PDS concentration of 2 mmol/L, and an unadjusted initial pH, the degradation rate of TC reaches 94.6% after 120 min of reaction. In addition to common free radicals (SO·−4 and HO · ), the active species in the S–nZVI/PDS system include the non-radical active substance Fe(Ⅳ), which has a minor effect on TC degradation. The primary pathways of TC degradation involve specific functional group cleavage and ring-opening reactions, ultimately leading to oxidative degradation into CO2 and H2O. © 2024 Sichuan University. All rights reserved.