Preparation Of Carbon Nano-tubes/TiO₂/chitosan Film And Photocatalytic Oxidation Of Indoor Benzen

At present, the pollution of indoor air has considerably been taken attention abroad as an important environmental problem. Benzene as ubiquitous pollution species in the air is considered to cause cancer by international agency for research on cancer. The effective treating process for decomposing benzene has been increasingly concerned. Photocatalysis as advanced oxidation technology, the use of photocatalytic oxidation of electron-hole pairs and a series of reactive oxygen species can remove most of refractory organic pollutants. It has proved very effective in environmental destruction of VOCs. Photocatalytic active catalyst of carbon nanotubes/TiO2/chitosan (CNTs/TiO2/CS) film was prepared. Degradation mechanism and kinetic model of CNTs/TiO2/CS film for indoor benzene were studied, and experimental study to verify the validity of the model. The influence of the indoor air conditions such as pollutant initial concentration, volumetric flow rate of the pollutant, relativity humidity and irradiance is considered in this model. It combines model of IAQ and model of building materials dissemination of VOCs, and performance of household cleaning air conditioning was studied. The main contents and results in this thesis can be summarized as follows:Different carbon nanotubes content of carbon nano-tube/TiO2(CNTs/TiO2) nanocomposites were prepared using a conventional sol-gel method. To further obtain a uniform catalyst film, chitosan (CS) was used as a crosslinker for the CNTs/TiO2composite. Characterization results show that TiO2particle covered carbon nanotubes surface and CNTs/TiO2composite dispersed in the chitosan matrix. The photocatalytic degaradation of benzene was chosen as a model reaction to evaluate the photocatalytic activities of the catalyst film. An optimum of the synergetic effect was found for a carbon nanotubes doped with2%(weight ratio)(CNTs(2%)/TiO2/CS). The intermediates of the photocatalytic degradation were investigated by FT-IR and GC/MS, of which ethyl acetate and hendecene were two major products and minor intermediate products were acrolein4-carbonyl-methyl-acetophenone,12-alkane,2,4di tert butylphenol and21-alkane. According to the analysis data of FT-IR and GC/MS, the photocatalytic degradation mechanism of the composite film was illuminated.The kinetic equation of photodegradation benzene was established based on elementary reactions of the reaction of the photocatalytic oxidation of benzene. The light intensity of the catalyst surface was calculated by the LSSE light radiation model. A model of photocatalytic oxidation of gas phase benzene was build together with the law of conservation of mass by a flat-plate reactor as photocatalytic oxidation reactor. The influence of the indoor conditions such as light intensities, relativity humidity, flow rates and initial concentrations is considered in this model.The influences of single factor and multi-factor were completed by experimental study on light intensities, relativity humidity, flow rates and pollution initial concentrations. The good agreement between the predictions from the model and the experimental results indicates the validity of the proposed kinetic model. A synergetic effect was found for photocatalytic oxidation benzene among the concentration field, radiation field and fluid mass transfer. Using multivariate analysis method, the relations of geological and influence factors of photodegradation of benzene are set up on light intensity, relativity humidty, flow rate and pollutant initial concentration. The degree effect of different factors is studied by multi-factor sensitivity analysis, and the influence of flow rate is more pronounced for photodegradation of indoor benzen.The effect of the efficiency of photocatalytic purifiers on concentration of VOCs· in indoor was investigated by considering the VOCs emission model of building materials and IAQ model. The results show that:When the purification efficiency of clean air conditioning is more than40%, it is small for influence degree of the purification efficiency on concentration distribution of indoor VOCs. For return air of air-conditioning and wind speed, it is linear relationship between the logarithm of purification time and purification efficiency. Compare to indoor wind speed, effect of return air is significant. These studies provide a theoretical reference design for household cleaning air-conditioning.