| Transparent mesoporous gel monoliths formed by the templation of surfactant, showed potential applications in the design of novel optical devices, such as lenses, chromophores, laser devices, non-linear optical media, and so on. This is because they can make guest molecules, such as dye molecules, photosensitive molecules, semiconductor particles or conducting nanowires, etc, not assemble to each other at higher concentrations of embedding due to the high transmission, low external surface area and inherently ordered adjustable pore structure.However, nowadays it is reported at home or abroad that most of transparent mesoporous gel materials are made of pure silica framework. It is obvious that the neutral framework structure is against the strong interaction with guest molecules, such as dye molecules, which are doped, tend to be charged or have strong polarity. It is also not conducive to the improvement of the stability of optical material, and difficult to control the distribution and migration of the guest molecules validly in internal channel of gels in order to achieve the control of the optical properties of materials by adjusting the synthetic processHence, the systematic study whose result can control the charge properties of the framework of the hybrid mesoporous gels on doping vario-property of heteroatom in the neutral framework of transparent mesoporous silica gel monoliths has an important theoretical research value and potential industrial application background. Obviously, when metal heteroatoms are incorporated in the synthesis system of pure silica gels in order to improve the charge ability of gel framework, the difficulty of controlling the transparency and integrality of the ultima hybridized gels will be increased.According to the above problems, this paper has made the study on the preparation of controlling the large-size、crack-free and transparent mesoporous silica-alumina gel monoliths. It has made transparent mesoporous silica-alumina gel monolithic material with ratio of gel Si/Al ranging from 3 to 80 in acid medium of nonionic surfactant as template, firstly using the cheap aluminium salt as aluminium source. What’s more, it has made the systematic research on the characterization of synthesized rule that will provide a matrix material with a new load of electrical adjustable for the development of new optical devices. Meanwhile, in comparison to the traditional mesoporous silica-alumina powder materials, gel monolithic material after calcinning and removing template of synthesis sample has better operability and can be applied in acid catalysis areas. The main results are as follows:1. The large-size, crack-free and optical transparent mesoporous silica-alumina gel monoliths with the Si/Al molar ratios ranging from 5 to 80, has been controlled preparation by adjusting the ratio of synthesis and using one-step assembly method, nonionic surfactant P123, F127 or Brij56 as template, TEOS as silicon source, Al(NO3)3·9H2O as aluminuim source, and HCl as hydrolysis catalyst of silicon source in acidic medium under 60℃.Then the synthetic rules has been systematic studied. It showed that with the introduction of Al atoms, it not only reduced the gelation time, but also helped the final gel dry stripping. But the influence on the size of gel pore size was limited. By changing the properties of the template agent used in the study, the specific surface area, pore size and pore volume of mesoporous silica alumina gel can be adjusted in the range of 340.28～758.13 m2/g,2.10～3.70nm and 0.297～0.445 cm3/g, respectively.From the analysis on the 27Al MAS NMR spectrum of synthesized sample of transparent monolithic mesoporous silica alumina gel, it showed that there were mainly four coordination framework and six coordination non-framework Al species in gel with Si/Al=5, and the five coordination Al species in the traditional mesoporous silica-alumina materials with low Si/Al molar ratios did not exist. It was clear that the existence form of the two different forms of Al atoms in gels and their charge which is hoped to be used in the development of novel optical devices would have different impact on the doped guest molecules, and can be adjusted by changing the Si/Al molar ratios of the synthetic system. The study on the NH3-TPD of mesoporous silicon-aliminum gel monoliths calcined removing template revealed that the acidity of samples would gradually enhanced with the increase of Al contents.2. The large-size, crack-free and optical transparent mesoporous silica-alumina gel monoliths with the Si/Al molar ratios ranging from 3 to 80, has been controlled preparation by first directly using the weak acid of aluminum salt solution to induce the hydrolysis of silicon source, using one-step assembly method, nonionic surfactant P123, F127 or Brij56 as template, and TEOS as silicon source under 60℃. Without the corrosive acid as catalyst, it has not only reduced the pollution to the environment and the synthesized costs of materials, but also made the Si/Al molat ratio as low as 3 and ensured the integrity of gels to further expand the adjusting range of gel silica alumina ratio. The results of the system revealed that the mesoporous silica-alumina gels in different synthetic systems had similar pore structure and acidity characteristic. By changing the properties of template, the gel specific surface area, pore size and pore volume can be adjusted in the range of 397.08～758.40 m2/g,2.13～ 3.58nm and 0.177～0.177cm3/g, respectively. The analysis on 27Al MAS NMR spectras of synthesized and calcined samples showed that Al mainly existed in the form of four coordination framework and six coordination non-framework at the lowest ration of Si/Al, and during the calcination, some of the four coordination Al species have the tendency to the six coordination. But compared with adding acid system, the weaker acid will help more Al atoms into gel framework.Through the study, with the high content of Al atoms the doping modification of transparent monolithic mesoporous silica gel was obtained firstly, the mesoporous gel framework components have been enriched, the effective ability of the electrical charge in the gel channel micro zone environment has been achieved, and the controlled preparation technology of large-size and transparent mesoporous gel monoliths and its application scope have been further verified and expanded. The synthesis of transparent mesoporous gel monoliths has provided a various choices for the modification of incorporated dye and the adjustion of optical properties of materials. And the study has an important theoretical research value and potential industrial application background for the development of novel optical devices. |
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