Electron transfer enhancing Fe(II)/Fe(III) cycle by sulfur and biochar in magnetic FeS@biochar to active peroxymonosulfate for 2,4-dichlorophenoxyacetic acid degradation

Abstract

Abstract A highly active mediator (magnetic FeS@biochar, MFB) for peroxymonosulfate (PMS) activation was prepared by employing FeSO4·7H2O and poplar sawdust as the precursor, for pesticides remediation in soil and groundwater. The magnetic FeS@biochar prepared at 500\xa0°C (MFB-500) did not only showed good performance in activating PMS to degrade 2,4-dichlorophenoxyacetic acid (2,4-D), but also longer lifetime. Due to the introduction of FeS, the defect degree of MFB-500 was higher according to Raman spectra result and favored in PMS activation. The X-ray photoelectron spectroscopy (XPS) and Mossbauer spectra confirmed that sulfur species promoted the regeneration of Fe(II). Moreover, EPFRs also showed an electron shuttle to enhance the recycle of Fe(II)/Fe(III) and increased the PMS activation performance. Electron paramagnetic resonance (EPR) spectroscopy identified SO4•-, •OH and 1O2 as the reactive oxygen species (ROS) in 2,4-D degradation. The optimized reaction parameters of MFB-500/PMS were determined as [MFB-500]\xa0=\xa0700\xa0mg/L, [PMS]\xa0=\xa02.6\xa0mM, [2,4-D]\xa0=\xa00.045\xa0mM. Meanwhile, the interfacial adsorption and catalytic reaction of 2,4-D degradation by MFB-500/PMS is accurately described by a newly mixed order kinetics model with adsorption and decay dominant rate constants kα and kγ, respectively. The effect of pH0 and coexisting anions was also studied, and it was found that acidic conditions are conducive to the degradation of 2,4-D, while alkaline conditions inhibited. Cl-, NO3– and SO42- play a slight inhibitory effect, and HCO3– and H2PO4- will play a significant inhibitory effect. This work provides a promising approach to the rational design of high-performance active mediators for environmental remediation.