Activation of peroxymonosulfate by molybdenum disulfide-mediated traces of Fe(III) for sulfadiazine degradation

The activation of persulfate by ferrous iron (Fe(II)) is of great interest to the environmental remediation community, but the reduction of ferric iron (Fe(III)) to Fe(II) is slow and the accumulation of iron sludge resulted from the precipitation of Fe(III) is a great concern. Here, molybdenum disulfide (MoS₂) was studied as a co-catalyst to improve the activation of peroxymonosulfate (PMS) by Fe(III) for sulfadiazine (SDZ) degradation and different characterization technologies were used to reveal the reactive species. The results showed that a strong synergy existed between MoS₂ and Fe(III); approximately 94.3% of the SDZ was removed by MoS₂-Fe(III)-PMS after reaction for 30 min, while only 8.5% and 56.4% of the SDZ was removed by Fe(III)-PMS and MoS₂-PMS, respectively. Both hydroxyl radicals and sulfate radicals were generated and the latter was the primary species. In addition to the radicals, singlet oxygen was found to be generated and contributed to the degradation of SDZ. The chemical probe reaction with methyl phenyl sulfoxide showed that the generation of high-valent iron-oxo species was not obvious by MoS₂-Fe(III)-PMS under both acidic and neutral conditions. MoS₂ had good stability. No noticeable deactivation was observed during the 1st to 5th run and no obvious oxidation of surface Mo(IV) occurred. Based on the characterization of catalyst and oxidizing species, a mechanism for the activation of PMS by MoS₂-Fe(III) was proposed. The results from this study are expected to clarify the reactive species and deepen the understanding of MoS₂-promoted persulfate activation by Fe(II)/Fe(III).