| With the continuous development of modern industry, the number and the type of organic matters enter into water through a variety of ways increased dramatically, the complexity and diversity of organisms, causing serious water pollution, in which toxic and hard degradation organic wastewater pollution is the most serious.TiO2 plays a significant role in the photocatalytic degradation for many environmental pollutants,which become the first choice for wide use in photocatalysis, ion exchange, molecular sieves, adorption and separation applications, photocatalysis has become a new type of environmental pollution control technologies. However, the band gap of TiO2 catalyst is large (Eg=3.2eV for anatase), TiO2 is active only in UV light can only absorb a small fraction of solar energy, which limits its commercial applications. Doping is the core of photocatalytic technology, it is indispensable to improve the photocatalytic activity of TiO2 under visible-light irradiation. Doping is one of the most effectively approaches and it has become a hot research topic. In this thesis, valuable explorations have been carried out on the fabrication, characterization, photocatalytic activity and the kinetic of methyl orange decomposition under the treatment of Pb2+-Si02-TiO2 catalys. The main points could be summarized as follows:(1) In this thesis, using tetrabutyl titanate (TBOT) and tetraetethyl orthosilicate (TEOS), lead nitrate (Pb(NO3)2) as raw materials, hexadecyl trimethyl ammonium bromide (C19H42BrN, CTAB) as template agent, has been successfully synthesized Pb2+ doped composite catalyst by via sol-gel reactions.The effect of Pb2+ doping amount and calcination temperature on the photocatalytic activity was investigated, and determine the best preparation conditions of composite catalyst under simulated sunlight. Then the prepared materials were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Fourier transform infrared spectrophotometer (FT-IR), ultraviolet-visible (UV-Vis), and so on. The experimental results showed that photocatalytic activity of TiO2 are greatly improved after mixing the right amount of Pb2+, Pb2+ doping increases the transformation temperature from anatase into rutile and minimises crystallite size. The optimum doping concentration is 100:1.5 (TiO2/Pb2+ mole percent), the optimum heat treatment temperature is 500℃.(2) Under simulated sunlight, the photocatalytic activities of Pb2+ doped silicon-titanium composite samples were evaluated by the result of photocatalytic degradation of methyl orange as a model reaction. The effects of pH,catalyst dosage, H2O2 amount and other factors on the treating efficiency were discussed.The experimental results showed that the methyl orange decolorization rate can research over 90.00% under the conditions of pH=4, catalyst dosage 3.0g/L, H2O2 amount 3mL/L, reaction time 180min and the concentration of methyl orange 10mg/L, but CODCr emoval effect is not very obvious.In the comparative experiment, photocatalytic properties of SiO2 doped TiO2 compared to Pb2+ doped TiO2 has more significant improvement, the catalytic performance of Pb2+-SiO2-TiO2 is best. It can be seen that appropriate Pb2+ and SiO2 co-doped TiO2 can significantly improve the performance of TiO2 photocatalytic properties. In addition, With the increase of the using frequency, the degradation rate of methyl orange decreased gradually, the first 3 times repeated use, the performance of Pb2+-SiO2-TiO2 composite catalyst reduce not very clear, decolorization rate of methyl orange reduce from 90.66% to 87.23% and lower into 82.3%, After continued use, Pb2+-SiO2-TiO2 catalyst performance has changed dramatically, and the degradation is poor.(3)It is complex to study the kinetics and mechanism for photocatalysis degradation of organic contaminants.The kinetics of methyl orange decomposition was investigated. The higher the concentration of methyl orange, the degradation rate is greater in the same time; the higher the concentration, the degradation which the catalyst has a large amount is better. The results showed that the reaction could be described by Langmuir-Hinshelwood equation (initial concentration 5.0mg/L-20.0mg/L) and was a apparent first-order reaction. |
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