Electro-enhanced heterogeneous activation of peroxymonosulfate via acceleration of Fe(III)/Fe(II) redox cycle on Fe-B catalyst

Abstract

Heterogeneous catalytic oxidation based on iron species for peroxymonosulfate (PMS) activation is considered as one of the most attractive strategies for wastewater treatment. However, the rate-limiting regeneration of Fe(II) from Fe(III) heavily hampers the efficient activation of PMS. In this study, the introduction of electric field to the Fe-supported bentonite (Fe-B) activated PMS process was proposed to enhance the Fe(III)/Fe(II) redox cycle. The Fe-B catalyst performed well in the removal of Acid Orange 7 (AO7) through the synergistic effect of electrolysis and the continuous redox cycle of Fe(III)/Fe(II) for PMS activation. The use of 0.5 g L−1 Fe-B catalyst and 10 mM PMS yielded nearly complete removal of the AO7 (50 mg L−1) in 60 min at 2 mA cm−2 of current density. Based on the results of electron paramagnetic resonance (EPR) spectroscopy, chemical quenching tests, X-ray photoelectron spectroscopy (XPS) analysis, and electrochemical measurements, the decolorization of AO7 was dominantly attributed to surface-bound radicals (SO4•−ads and •OHads) and also the direct electron transfer at DSA anode. Moreover, the electro/Fe-B/PMS system showed an effective pH range from 2.6 to 9.0 and the abatement of AO7 was slightly affected in the presence of natural background anions. This work provides a feasible strategy of PMS activation by cost-effective Fe-B catalyst coupling with electric field and gives an insight into the accelerated oxidation of recalcitrant pollutants.