Mechanism of influence of initial pH on the degradation of nitrobenzene in aqueous solution by ceramic honeycomb catalytic ozonation

The influences of initial pH on the degradation efficiency of nitrobenzene in aqueous solution were investigated with a semicontinuous batch reactor in the processes of ozone alone, ozone/ceramic honeycomb, and adsorption of ceramic honeycomb. The results indicated that initial pH significantly affected the concentrations of offgas, residual ozone, and the utilization efficiency of ozone. The experiments also detected the generation of hydroxyl radicals ((OH)-O-center dot),the removal of TOC, and the formation and evolution of byproduct at different initial pHs in the ceramic honeycomb catalytic ozonation process. It was found,that the systems of different initial pHs exhibited the different extent of the conversion of pH, the leaching of effective components, and the establishment of pH at the point of zero charge (pH(PZC)) in the catalytic oxidation process. The experimental findings presented a good correlation between initial pH and terminal pH and the establishment of pH(PZC) with terminal pH, and indicated the relationship between the absolute value of the difference between terminal pH and terminal pH(PZC) (A) and the density of surface hydroxyl groups. Based on the correlation between the density of surface hydroxyl groups in the neutral state and A, possible mechanism of influence of initial pH on the degradation of nitrobenzene in aqueous solution by ceramic honeycomb catalytic ozonation was proposed, suggesting that the conversion of initial pH determines the establishment of pH(PZC), and the synergistic effect of pH(terminal) and pH(PZC) (terminal) affects the density of surface hydroxyl groups,in the neutral state, which controls the concentration of (OH)-O-center dot, determining the degradation of nitrobenzene and the formation of byproduct