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

BACKGROUND Mixed‐valence manganese oxide nanoparticles (nano‐ MnO x ) were prepared by the oxidation of Mn ( II ) with Mn‐oxdizing bacteria Pseudomonas sp. G7 . The chlorophenols transformation process was studied in detail. RESULTS The 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‐ MnO x ‐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 •‐ ) predominantly came from the interaction of oxygen in air with the reduced manganese in nano‐ MnO x on the basis of the studies of electron spin resonance and all other information. CONCLUSION The mixed valence in nano‐ MnO x ‐1 enhanced the formation of O 2 •‐ , 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 •‐ in nano‐ MnO x ‐1 suspension. This finding indicates the potential of nano‐ MnO x for the elimination of unbiodegradable chemicals in water. © 2013 Society of Chemical Industry