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.