Decolorization of methyl orange by MnO2/organic acid system: The role of Mn(III)

Abstract

Decolorization of methyl orange (MO) by MnO2 was investigated with and without small molecules of organic acids such as formic acid. It was found that the decolorization could be significantly improved by MnO2 with the assistance of organic acids. The effect of various conditions was investigated on MO decolorization by using different crystal types of MnO2 and changing the types of organic acids. One of the optimum treatment conditions was δ-MnO2/formic acid system, which led to the removal efficiency of 90.6% at 30 min. The pseudo-second-order kinetic rate constant of δ-MnO2/formic acid was 0.1626. A reasonable decolorization mechanism involving Mn(III) species was proposed and the mechanism was validated by simple detection of ionic species such as, Mn(II) and Mn(III) during the reaction. The δ-MnO2/formic acid process designed here may lead to a new advanced oxidation technology based on the in-situ generation of active Mn(III) species and their ability for oxidation.