| The nanometer TiO2, as an important chemical raw material, has its excellent physical and chemical performance and has widely been used in the fields of astronavigation, electronics, metallurgy, chemistry, biology and medicine. The dispute on the method of testing particle size and the attractive potential usage of photocatalysis make the study on the preparation technology of nanometer TiO2 and the method of improving its photocatalysis become one of the highlights in physics, chemistry and material science. The work in this dissertation is focused on exploring an easy-to-operate, low-cost and versatile analysis method of particle size and preparing of TiO2 with modification on its suface. We also research into the preparation of ZnS,ZnO/TiO2 composite particles using three different methods, and make a deep study of the feature, crystal form, composition and photocatalysis performance change of modified nanometer TiO2 and composite particles basing on these methods.The reliablity of particle size measuring is on the premise that the particles are fully separated and have no agglomeration. So we work on the improvement of testing conditions for representative nanometer particles(TiO2?Al2O3?SiO2) in the aspects of sample concentration, dispersion medium, dispersant, ultrasonic treatment time, obtain appropriate experiment conditions after optimization and build up the method to measure ultrafine particle size using centrifugal sedimentation light transmission. By using this method, we have successfully tested the TiO2, SiO2, nano-ultrafine Al2O3 particles, homemade nano-TiO2 samples and super-micro manufactured powders produced by American NANO TEK company, and the experiments indicate that centrifugal sedimentation light transmission method can be applied to testing ultrafine particles about 100nm in diameter. Through the comparison with the results measured by laser scattering and transmission electron micresciopy(TEM), our results are reliable. Compared with other existing methods to measure ultrafine particle siz, it has such adavantages as easy operation and low detection cost, and is worth promoting.We have successfully prepared nano-TiO2 ultrafine particles by thermal decompositon and made surface hardening modification by using dimethyl silicone oil. This modification makes the infra-redspectrum of nano-TiO2 material change around the rang of 1000-550cm-1 and shift to lower frequency, which indicates response spectrum expands to visible light, related bandgap energy bocomes lower and controls the complex of current carriers effectively and improve its photocatalysis efficient. In addition, it makes the aggregates of carriers lower and enhances molecular dispersivity. TiO2 is easily settled in water, but TiO2 modified by dimethyl silicone oil has the character of strong suspension property, and can suspend on methyl orange aqueous solution or surface and superficial layer of other waste water. Besides, it can sufficiently absorb external light source, which is extremely beneficial to directly make use of solar energy. Meanwhile, this modification doesn't have obvious effect on phase, grain size and crystallinity of the material.Compared with non-modified nano-TiO2, the nano-TiO2, which is made surface hardening modification by using dimethyl silicone oil, has the following characters:viscosity rises clearly, and steady suspension liquid is easily obtained; it has strong degradation effect on the VOC in dope. But whether being modified or not doesn't have much effect on th contrast ratio of dope, which has something to do with particle size and distribution of paint.When adding nano-TiO2 modified with special photocatalysis into interior wall ecology dope, the stablity of suspension property can be improved and the new coating will own the advantages of excellent air cleaning, bacteriostatic effect and so on. This effect will play a significant role in the cleaning of harmful gases caused by indoor decoration.By the three methods of physical mixing, homogeneous precipitation and surface precipitation, ZnS/TiO2 composite powders,whose doping molar ratio is 1:10, have been successfully prepared and have been characterized by using such technologies as XRD, SEM, IR and XPS. The differences of photocatalytic degradation of methyl orange among the samples prepared by three methods are explored. Linking with surface constitution, bandgap energy etc., the photocatalytic mechanism of ZnS/TiO2 composite powders is also discussed. The result shows that three kinds of composite powder are mostly spherical shape. The reason for physical mixing preparation of the ZnS/TiO2 composite powders is that after a thorough mixing, more uniform mixing, agglomeration is relatively small. The particle size of the powder prepared by homogeneous precipitation is smaller, only 10.8nm, which is layered reunion. ZnS/TiO2 nano-composite powder prepared by homogeneous precipitation, whose XRD pattern of ZnS crystal form is not clear, the content is very low, and peak may be covered by TiO2 crystal. The bandgap energy of three composite powders can be measured by using solid UV-Vis spectroscopy. The bandgap energy of physical mixing is 2.69 eV; the bandgap energy of surface precipitation is 2.66 eV; and the bandgap energy of homogeneous precipitation is 2.70 eV. The difference among the three methods is small, but they are both clearly smaller than the bandgap energy of a single nanometer TiO2, ZnS powders. The order for the activity of degradation of methyl orange of nano composite powders ZnS/TiO2 prepared by three methods is:surface precipitation>physical mixing> homogeneous precipitation. The bandgap energy determination results of three kinds of composite powders agree with the activity of photocatalytic degradation of methyl orange. Three kinds of composite powders have shown greater photocatalytic activity than a single semiconductor.By the three methods of physical mixing, fractional precipitation and homogeneous precipitation, ZnO/TiO2 composite powders, whose doping molar ratio is 1:10, have successfully been prepared and have been characterized by using such technologies as XRD, SEM, IR and XPS. The differences of photocatalytic degradation of methyl orange among the samples prepared by three methods are explored. Linking with surface constitution, bandgap energy etc., the photocatalytic mechanism of ZnO/TiO2 composite powders is also discussed. The result shows that:the feature, crystal form and composition of three kinds of composite powders have some differences. The experiment results of the methyl orange degradation of ZnO/TiO2 nano-composite powders prepared by using the above three methods show that the activity order is:physical mixing>fractional precipitation> homogeneous precipitation. Three kinds of composite powders have shown greater photocatalytic activity than a single semiconductor. Bandgap energy of three composite powders can be measured by solid UV-Vis spectroscopy. The bandgap energy of physical mixing is 2.81 eV; the bandgap energy of fractional precipitation is 2.87 eV; the bandgap energy of homogeneous precipitation is 2.98eV. Their bandgap energies have some differences, but are clearly lower than TiO2 and ZnO bandgap erengy. The result shows that after doping ZnO, composite powder surface electron-hole pairs on the compound are decreased, And bandgap narrowing will make light absorption efficiency of composite powder increased. The electron spectroscopy of composite powders indicates that Zn:Ti ratio in the ZnO/TiO2 composite powders prepared by physical mixing is the highest. The relative increase in the content of Zn2+ can reduce the composite powder surface electron-hole pairs on the compound, which produces more·OH and O2- on the composite powder surface.·OH and O2-in the catalytic process play a major role. This result is consistent with the low bandgap erengy and high catalytic activity of the ZnO/TiO2 composite powders prepared by physical mixing. Composite powders prepared by different methods have different photocatalytic properties closely related with their form and structure. |
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