Efficient Mn(III)-oxalate generation for diclofenac oxidation by electro-reduction of potassium permanganate in the presence of oxalate

Abstract

Although electrochemical activation of permanganate (E-PM) is a green and efficient method to degrade refractory organics by in-situ generated reactive Mn(III)aq, this process highlights on the presence of promoter and/or stabilizer. Oxalate (OA) is a widespread organic chelate in natural water bodies (with concentrations up to 1 mM), but whose effect on the E-PM process is still unclear. In this study, we found electrolysis and the presence of OA both promote the activation of PM for the degradation of diclofenac (DCF), showing a high synergistic coefficient (3.23) and elevated reaction constant (0.1395 min−1). Nevertheless, this process is highly pH-dependent, behaving decreased reactivity as pH value increasing from 3 to 11. Sufficient concentration of OA (≥0.5 mM in this study) is required for stabilizing Mn(III). UV–vis spectra, visual evidence and quenching experiments identified the presence and dominant role of Mn(III)-OA on the degradation of DCF. Using chronoamperometry, we confirmed Mn(III)-OA was primarily generated from the electro-reduction of PM in the presence of OA at pH 5.