| Carbon tetrachloride(CCl4) is one kind of non-flammable volatile organic compounds(VOCs), which has be used as leaching agent of spice, cooking agent of food, extraction agent of drug, degreasing agent of fiber, organic chloride agent, lubricant in metal cutting, and can also be used for synthesizing freon, nylon 7 and nylon 9. Due to stable chemical property and high biotoxicity, CCl4 released into natural environment may cause long-term adverse effects. Moreover, owing to the features of higher volatility and lipid solubility CCl4 could be absorbed into the body through skin and mucosa, resulting in irreversible biohazard to liver and other organs, and causing the seriously adverse effects on human health. So the Environmental Protection Agency of the United States(U.S EPA) has listed it into one of the priority control pollutants. In some developed areas of China, extensive use of CCl4 and long-term excessive emissions of industrial waste water, CCl4 has become one of the main pollutants in water system. The environmental quality standards in China for surface water is GB3838-2002, which clearly put forward that the CCl4 content in drinking water should be limited to 2ug/L. To reduce and eliminate the hazards of CCl4 on the living environment of human beings, the degradation, conversion and replacement for the existing CCl4 should be an advisable and efficient path.This work mainly involves the following contents:(1) Setting up the method of purge and trap–gas chromatography/mass spectrometry(P&T-GC/MS) to measure CCl4 in water. The study involves optimizing capture trap packing, purging time, temperature and quantity of flow, analytical time, temperature and quantity of flow, baking temperature, temperature and quantity of flow, and so on. The researches including injection port temperature of the gas chromatography, chromatography column packing, temperature program, carrier gas flow rate and split ratio are all carried out. A solid foundation for the accurately measuring the content of CCl4 in aqueous solution has been suggested.(2) The photocatalyst, BiOBr, has been synthesized through hydrothermal treatment with the assistance of surfactants, and the resulting products were characterized by x-ray powder diffraction and scanning electronic microscope.(3) The visible light catalytic oxidation of CCl4 in aqueous solution using Bi OBr as catalyst has been made. The detailed investigation of CCl4 degradation process in solution under such conditions as exposure time, p H value, BiOBr catalyst dosage and visible light power has provided us the optimal configuration for these main factors. By orthogonal design method, the optimal scheme of the degradation experiments has been obtained, and experimental results have also been scientifically analyzed. At the optimum conditions, the primary affecting factors for the oxidation degradation of CCl4 solution were further studied.(4) The kinetic constants under different p H values were obtained. The reaction rate constants of CCl4 for the catalytic degradation reaction have been fitted and calculated, and the mechnism of CCl4 degradation reaction under visible light irradiation was briefly explained. |
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