Ascorbic acid enhanced the zero-valent iron/peroxymonosulfate oxidation: Simultaneous chelating and reducing

Abstract

The activation of peroxymonosulfate (PMS) with zero-valent iron (Fe(0)) generates reactive oxygen species that can effectively degrade aromatic organic contaminants. However, the low conversion rate from Fe(III) to Fe(II) and the aggregation of iron sludge restrict its wide application. In this study, a water-soluble vitamin, ascorbic acid (H2A), was combined with the conventional Fe(0)/PMS system to enhance the degradation of benzoic acid (BA). The removal efficiency of BA in the H2A/Fe(0)/PMS system was improved by 59.4% compared with the conventional Fe(0)/PMS system under the optimal conditions of 0.03 g/L Fe(0), 0.4 mM PMS, 0.1 mM H2A and initial pH of 4.5. This result was mainly credited to the excellent reducing and chelating ability of H2A, which promoted the generation of reactive oxygen species by accelerating the reduction of Fe(III) and forming Fe(III)-ascorbate complexes. Alcohol quenching and electron spin resonance (ESR) experiments demonstrated that the main reactive oxygen species for the degradation of BA in the H2A/Fe(0)/PMS system were •OH and SO4∙-. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) analyzed the surface chemistry and phase transformation of fresh and used Fe(0). Based on the above experimental analysis, the degradation mechanism of BA in the H2A/Fe/PMS system was systematically explored. Common water matrix including Cl-, HCO3-, NO3- and humic acid inhibited the degradation of BA, while SO42- had negligible impacts. In addition, the degradation performance of the H2A/Fe(0)/PMS system in natural water environment and its degradation of various pollutants were also investigated. In summary, this study provides new insights for enhanced removal of refractory organics by improving the conventional Fe(0)/PMS system.