Characteristic mechanism of ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies for the degradation of nitrobenzene in aqueous solution

Ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies was carried out in semi-continuous mode to investigate the degradation efficiency of nitrobenzene in aqueous solution. The combination process can enhance remarkably the degradation efficiency of nitrobenzene compared to the additive effects of single operations, and the degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. The enhancement function is even more pronounced in the presence of ultrasound with orthogonal triple frequencies due to the obvious synergetic effect which can accelerate the transformation and the decomposition of ozone, increase the utilization efficiency of ozone, and enhance the initiation of OH and the formation of H2O2, resulting in the rapid formation of an increasing diversity of byproducts and the higher degree of mineralization of total organic carbon. The investigation of enhanced mechanism indicates the introduction of ultrasound can prevent deactivation by continuously cleaning the surface of catalyst, and can accelerate the cleavage of the bond as well as speed up the diffusion of oxidative intermediate from the heterogeneous surface to the aqueous solution due to the weakening of the bond derived from the ultrasonic shock, leading to the production of the synergetic effect among ozone, ceramic honeycomb and ultrasound.