Regulating the redox centers of Fe through the enrichment of Mo moiety for persulfate activation: A new strategy to achieve maximum persulfate utilization efficiency

Persulfate Fe-based catalytic oxidation is considered as one of the most attractive strategy for the growing concerns of water pollution. However, the undesirable Fe^III/Fe^II redox cycle restrict them from attending the sustainable activity during practical applications. This study was intended to develop a new strategy to regulate the redox cycles of Fe^III/Fe^II by introducing the second redox center of MoS₄²⁻ in the interlayers of Fe-based layered double hydroxide (FeMgAl–MoS₄ LDH). Based on the first-order kinetic model, the fabricated FeMgAl–MoS₄ catalyst was 10–100 fold more reactive than the bench marked peroxymonosulfate (PMS) activators including FeMgAl LDHs and other widely reported nano-catalysts such as Co₃O₄, Fe₃O₄, α-MnO₂, CuO–Fe₃O₄ and Fe₃O₄. The enhanced catalytic activity of FeMgAl–MoS₄ LDH was related to the continuous regeneration of active sites (Fe^II/Mo^IV), excellent PMS utilization efficiency and generation of abundant free radicals. Moreover, the FeMgAl–MoS₄/PMS system shows an effective pH range from 3.0 to 7.0 and the degradation kinetics of parahydroxy benzoic acid (PHB) were not effected in the presence of huge amount of background electrolytes and natural organic matters. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR), chemical scavengers, XPS analysis and gas chromatography couple with mass spectrometer (GC-MS), a degradation pathway based on dominant free radicals (•SO₄⁻ and •OH), passing through the redox cycles of Fe^III/Fe^II and Mo^VI/Mo^IV was proposed for PMS activation. We believe that this strategy of regulating the redox center through MoS₄²⁻ not only provides a base to prepare new materials with stable catalytic activity but also broaden the scope of Fe-based material for real application of contaminated water.