Efficient catalytic aerobic oxidation of chlorinated phenols with mixed-valent manganese oxide nanoparticles

Abstract

BACKGROUNDMixed-valence manganese oxide nanoparticles (nano-MnOx) were prepared by the oxidation of Mn (II) with Mn-oxdizing bacteria Pseudomonas sp. G7. The chlorophenols transformation process was studied in detail. RESULTSThe materials were characterized by XRD, TEM-EDX, and XPS measurements. The characterization showed that mixed valence of Mn (II), Mn (III), and Mn (IV) existed in nano-MnOx-1 with the initial Mn (II) dosage of 0.4 mmol L-1. The catalyst was found to be highly effective, stable for catalytic aerobic oxidation of chlorophenols without any Mn (II) release from the catalyst throughout the reaction. Moreover, chlorinated phenols including 2-chlorophenol, 2, 4-dichlorophenol and 2, 4, 6-trichlorophenol, were partly converted into small organic acids. The formation of superoxide radicals (O-2(center dot-)) predominantly came from the interaction of oxygen in air with the reduced manganese in nano-MnOx on the basis of the studies of electron spin resonance and all other information. CONCLUSIONThe mixed valence in nano-MnOx-1 enhanced the formation of O-2(center dot-), resulting in the inhibition of Mn (II) release, maintaining the catalyst stable. Degradation of the tested chlorinated phenols was ascribed to the oxidation of Mn (III/IV) and O-2(center dot-) in nano-MnOx-1 suspension. This finding indicates the potential of nano-MnOx for the elimination of unbiodegradable chemicals in water. (c) 2013 Society of Chemical Industry