Enhanced transformation of phenolic compounds by manganese(IV) oxide, manganese(II) and permanganate in the presence of ligands: The determination and role of Mn(III)

Abstract

In this study, colorimetric methods using diethyl phenylene diamine (DPD), 2,2′-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), and potassium iodide (KI) were adopted to determine manganese(III)-pyrophosphate complex (Mn(III)-PP) in trace levels (10 µM). An ozonation method was developed to measure the concentration of dissolved Mn including Mn(II) and Mn(III) via quantifying permanganate (Mn(VII)) generation during ozonation of dissolved Mn with PP. The ozonation method combined with DPD method were applied to determine MnO2 dissolution kinetics in the presence of oxalic acid through monitoring MnO2 decay and Mn(III)/Mn(II) formation. PP and oxalic acid could enhance the oxidation of bisphenol A (BPA) by MnO2 at acidic pH, while no promoting effects were found at neutral pH. EDTA had enhancing effect on the oxidation of BPA by MnO2 at neutral pH but inhibiting effect at acidic pH. This result indicated high activities of Mn(III)-PP at acidic pH, Mn(III)-oxalic acid at acidic pH, and Mn(III)-EDTA at neutral pH, respectively. Enhancing effect of low concentration of humic acid (HA) on the oxidation of BPA by MnO2 at acidic pH, however inhibiting effect was found with high dosage of HA due to the occupation of HA on the active sites of MnO2. Furthermore, desferrioxamine B (DFO) was observed to accelerate the transformation of hydroquinone (HQ) with Mn(II) at alkaline pH, ascribed to the formation of Mn(III)-DFO from the reaction of oxygen with Mn(II) rapidly. Finally, a Mn(VII)-reducer-PP system for the transformation of phenolic compounds was evaluated. Two effective reducers (i.e., Mn(III) inducers), Mn(II) and bisulfite, could accelerate Mn(III)-PP formation in the initial step, and then promote the oxidation of phenolic compounds by Mn(VII). Transformation of phenolic compounds were enhanced by MnO2(IV), Mn(II) and Mn(VII) in the presence of ligands due to the generation of Mn(III), which reflected the potential application value of Mn(III) in micro-polluted water treatment.