Ascorbic acid-assisted iron silicate composite activated peroxydisulfate for enhanced degradation of aqueous contaminants: Accelerated Fe(III)/Fe(II) cycle and the interaction between iron and silicate

In this study, an ascorbic acid (AA)-assisted iron silicate composite activated persulfate (ISC/PDS) process was developed for the degradation of sulfamethazine (SMT). Experimental results suggested that AA could significantly enhance SMT degradation by 72.4 % compared with the ISC/PDS process. The enhancement in SMT degradation mainly benefited from the accelerated surface Fe(III)/Fe(II) cycle and the interaction between iron and silicate. It was revealed that the promoted Fe(III)/Fe(II) cycle induced by AA and superoxide radical (O-2(center dot-)) favored the continuous activation of PDS. The formation of Fe - Si binary oxides on the surface of iron silicate composite promoted the electron transfer from iron silicate composite to PDS. Meanwhile, the formation of [Si - Fe(II)] complexes could avoid the rapid and invalid oxidation of soluble Fe(II). The ISC/PDS/AA process was confirmed to be a radical-dominated (i.e., hydroxyl radical ((OH)-O-center dot) and sulfate radical (SO4 center dot-)) oxidation process based on the quenching, electron spin resonance (ESR), and competition kinetics experiments. Additionally, the effects of several key influencing factors on degradation performance were studied. Degradation pathways of SMT and AA and their eco-safety of intermediates were also investigated. This work deepens the understanding of the iron-based catalyst for efficient heterogeneous PDS activation towards water decontamination with the assistance of reductant.