Catalytic Ozonation Of Organic Pollutants Over MnCeO_x Composites And MnO_x/TNT Oxide

Water pollution is very serious in our country, and more and more researchers have involved in the study of dealing with the water pollution. People pay close attention to the advanced oxidation technologies because it can produce a large number of free radicals. The advanced oxidation technologies include photochemical oxidation, catalytic wet oxidation, ozone oxidation, electrochemical oxidation, etc. Ozone oxidation method has many advantages, including decomposing refractory organics, fast and complete reaction, no secondary pollution produced, etc. In this work,MnCeO_X、Mn/TNT oxides were synthesized by environmentally friendly methods and characterized by XRD, TEM, XPS, FTIR and N2 adsorption-desorption techniques. The kinetics and mechanism of organic pollutants degraded on the typical catalysts were also studied. The results are listed as follows.(1) Preparation and catalytic ozonation performance of MnCeO_XMnCeO_X composites were prepared by a redox-precipitation method. We investigated the catalytic activity of MnCeO_X composite when it is in different proportion of manganese and cerium, different p H value, different calcination temperature and so on, and found the best condition of the preparation of MnCeO_X composite catalyst with redox process: 2:8 of the Ce/Mn mole ratio of reactants, 60°C of the reaction temperature, p H = 6, 2-hour mixing reaction, 350°C of 4-hour calcination in muffle furnace. The obtained catalysts were characterized by BET, XRD, TEM, SEM etc. techniques, and their catalytic performance for ozonation of antipyrine(AP) was studied by semi-batch experiments. Results show that the catalyst has the stronger ability of electron transfer, can effectively promote the decomposition of ozone into hydroxyl radical. The TOC removal efficiencies were above 80%. The final intermediate in the catalytic ozonation of AP was oxalic acid,and the intermediate mainly removed by hydroxyl radical.At low p H, organic matter and active sprcies reaction played an important role on the surface of the catalyst.(2) Preparation and catalytic ozonation performance of MnO_X/TNTManganese oxide supported on titanate nanotube(TNT) was prepared by an impregnation method and used as catalyst for ozonation of p-nitrophenol(PNP) in aqueous solution.Characterized by XRD, TEM, XPS, FTIR and N2 adsorption-desorption techniques. Results show that the synthesized catalyst exhibited high activity for the mineralization of PNP with ozone, and about 95% of total organic carbon was removed at 45 min. The degradation of PNP was mainly due to the oxidative process in solution, and hydroxyl radical reaction played an important role for the degradation of its ozonation products(formic acid and oxalic acid). The mesopores containing active components could serve as nanoreactors that facilitate the reactions between organic molecules and oxidative species, the highly dispersed Mn Ox accelerated the decomposition of adsorbed ozone into hydroxyl radicals. The negatively charged surface and surface acid sites of the support favored the adsorption of ozone, while the highly dispersed Mn Ox accelerated the decomposition of adsorbed ozone into hydroxyl radicals,thus improving the utilization rate of ozone and the mineralization rates of organic pollutants.(3) Mechanism and catalytic ozonation performance of MnO_X/TNT In this chapter we used Mn/TNT as catalyst for ozonation of salicylic acid(SA) in aqueous solution.Experiment results show that under the condition of acid, the mineralization of salicylic acid(SA) rate is more than 90%, and the catalyst has good recycling effect. In order to explore the mechanism of salicylic acid(SA) degradation further, we added different macromolecular organic acids such as citric acid, ascorbic acid, fulvic acid, small molecule inorganic acids such as oxalic acid, formic acid, succinic acid, benzene content such as toluene, phenol, gallic acid and explored their effects on catalytic ozonation salicylic acid by high performance liquid chromatograph. In addition the several common ions such as Na +, K +, Ca 2+ and Cl-, NO3-, CO32-, etc. were also added. We explored its catalytic ozonation degradation effect of salicylic acid mineralization rate by TOC analyzer.