Pivotal roles of MoS₂ in boosting catalytic degradation of aqueous organic pollutants by Fe(II)/PMS

Despite the success of Fe(II)/peroxymonsulfate (PMS) process in detoxifying organic pollutants, its intrinsic drawback of sluggish Fe(III) conversion to Fe(II) limits its large-scale practical application. Here we report that commercial MoS₂, a common metal sulfide, can be used to unlock this kinetic constrain. Addition of MoS₂ greatly accelerates the reduction of Fe(III) to Fe(II), decomposition of PMS, and thus results in enhanced degradation efficiency of 2,4,6-trichlorophenol (TCP) (>95%) and other biorefractory halogenated organic compounds within 30 min. Mass spectroscopy data indicate that TCP can be destructed into low-molecular-weight organic acids, manifesting its powerful oxidation capacity of MoS₂-assisted Fe(II)/PMS process. Once the Fe(III) in aqueous solution is stabilized by its organic or inorganic ligands, the boosting effects of MoS₂ are largely inhibited and less than 80% of TCP is degraded. Sulfate radicals and hydroxyl radicals are identified as the dominant reactive oxidants in the MoS₂/Fe(II)/PMS process by radical scavenging tests. The unsaturated S on the fresh MoS₂ surface and the exposed Mo(IV) sites are supposed to react with PMS and Fe(III) in the aqueous solution, respectively. No iron oxides and Mo oxides are detected in X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) measurement, indicating the accelerated Fe(II)/PMS process mainly occurs in the homogeneous solution. MoS₂ exhibits excellent recyclability and sustainable reactivity for the degradation of TCP after 5 consecutive runs. Overall, the present study provides a novel strategy to overcome the rate-limiting step of Fe(III)/Fe(II) that is commonly challenging Fe-based advanced oxidation processes (AOPs) and enable Fe(II)/PMS as efficient as typical Co(II)/PMS.