Zhizhong Sun

Influencing mechanism of temperature on the degradation of nitrobenzene in aqueous solution by ceramic honeycomb catalytic ozonation

The heterogeneous catalytic ozonation of nitrobenzene in aqueous solution has been carried out at different reaction temperatures in a semi-continuous batch reactor where ceramic honeycomb has been used as a catalyst. The experimental results indicated that the presence of ceramic honeycomb catalyst significantly improved the degradation efficiency of nitrobenzene compared to the results from non-catalytic ozonation, and the adsorption of nitrobenzene on the catalytic surface has no significant effect on its degradation efficiency. The degradation of nitrobenzene followed the pseudo-first-order kinetic model in both the processes of ozone alone and ozone/ceramic honeycomb. With the increase of reaction temperature from 278K to 328K, the degradation efficiency of nitrobenzene, the reaction rate constants, the utilization efficiency of ozone, the formation of hydroxyl radicals (*OH) and the removal of total organic carbon (TOC) all increased in the process of ozone/ceramic honeycomb. The enhancement of reaction rate constant and the enhancement of *OH formation exhibited a good correlation in the reaction temperature scope of 278-328K.

Preliminary kinetic study on the degradation of nitrobenzene by modified ceramic honeycomb-catalytic ozonation in aqueous solution

The kinetics of degradation of nitrobenzene in aqueous solution was investigated in the processes of ozone alone, ozone/ceramic honeycomb (CH), ozone/modified ceramic honeycomb (MCH). The results indicated that all reactions followed the pseudo-first-order kinetic model, and the degradation rate of nitrobenzene was accelerated in the presence of CH or MCH catalyst, and the more pronounced degradation rate was achieved in O(3)/MCH system. Under the experimental conditions of reaction temperature 293 K and initial pH 6.87, the rate constants were determined to be 5.21 x 10(-2)min(-1) for O(3) alone, 7.99 x 10(-2)min(-1) for O(3)/CH and 15.45 x 10(-2)min(-1) for O(3)/MCH. The influencing factors, such as applied ozone concentration (0.987-2.732 mg L(-1)), initial concentration of nitrobenzene (50-250 microg L(-1)) and amount of catalyst (0-5 blocks) could yield respectively the positive effect on the pseudo-first-order rate constants for degradation of nitrobenzene in the three processes mentioned above. The results suggested that the modification process promoted the catalytic activity of raw CH catalyst, namely the impregnation of metals (Mn, Cu and K) maybe enhance the initiation of hydroxyl radical (OH).

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.