Bisulfite triggers fast oxidation of organic pollutants by colloidal MnO2.

Abstract

Colloidal MnO2 is the most reactive phase of Mn(IV) while HSO3- is a common reductant in water treatment. This study shows that the presence of HSO3- resulted in significant increase in the decomposition rate of organic contaminants by colloidal MnO2. The degradation rate of contaminants in the MnO2/HSO3- process dropped with elevating pH and a proper MnO2/HSO3- molar ratio was critical for efficient decomposition of contaminants. The time-resolved spectroscopy of manganese species, the influence of pyrophosphate on UV absorbance spectra, and the relative rate constants of contaminants oxidation in MnO2/HSO3- process suggested that the synergetic effect of HSO3- and colloidal MnO2 arose from the generation of Mn(III)aq, which could oxidize contaminants rapidly. The presence of pyrophosphate, ethylenediaminetetraacetic acid, and humic acid depressed the degradation of contaminants in MnO2/HSO3- process by complexing with Mn(III)aq, buffering the solution or competing with contaminants for Mn(III)aq, and/or inhibiting the consumption of bisulfite. However, Ca2+ and Mg2+ accelerated the oxidation of contaminants in MnO2/HSO3- process by enhancing the reduction of MnO2 by HSO3-. The good negative correlation of the O/N or H Mulliken charges of organic contaminants with their removal in MnO2/HSO3- process suggested that organic contaminants were oxidized by Mn(III)aq via electrophilic attack.