Effect of pH on MnO_x/GAC catalyzed ozonation for degradation of nitrobenzene

The effect of pH on MnO_x/GAC heterogeneous catalytic ozonation was investigated. Nitrobenzene was used as a model refractory organic pollutant. It was found that in MnO_x/GAC catalytic ozonation, the degradation efficiency of nitrobenzene was higher under low pH conditions (pH 2.74-3.52) than that under high pH conditions (pH 6.72-9.61). This result was different from the case of ozonation alone, in which higher pH had positive effect on the degradation of nitrobenzene due to the formation of hydroxyl radical. In the presence of MnO_x/GAC catalyst, ozone decomposition was accelerated, and higher pH condition favored ozone decomposition. It was assumed that hydroxyl radicals might not be the dominating active species in the catalytic oxidation, for the presence of t-butanol did not have any influence on MnO _x/GAC heterogeneous catalytic ozonation. Adsorption of organic micropollutants on MnO_x/GAC catalyst was an important step and would have direct influence on the effectiveness of catalytic oxidation. It was assumed that the organic pollutants might be further decomposed on the surface of catalyst.