Synthesis And Study On The Core-shell Structures And Hollow Structures Materials

In recent years, with the development of technology of materials and Compositions, there has been great interest in concerning the synthesis of hollow structured materials with specific structures and different compositions. Composites with core-shell structure not only can combine the advantages of all ingredients, so their properties are better than any ingredient. And the control of their properties is easy because of the core-shell structure. So it has widely applications in many fields and has become a vital part in material research fields. Hollow materials are formed by removal of the core by a solvent or heating. Hollow materials have widely potential applications as delivery vehicles for the controlled release of drugs, dyes due to their special hollow structure. At present, the sol-gel method is the most widely way used to prepare these special particles.In order to improve the integration between magnesium hydroxide and the silane coupling agent, a sol-gel approach was used to prepare the Mg(OH)₂/SiO₂ core-shell composite particles . The influence of pH, temperature, different silicon sources and other factors on the preparation of the composite particles were studied. The measurement of SEM, TEM, EDS, FT-IR were used to characterize the chemical composition, morphology, size and superficial crystal structure of the particles. The results show that, good Mg(OH)₂/SiO₂ particles with core-shell structure can be prepared under the conditions of sodium silicate as silica source, pH 9 and 90℃. There are chemical bonds between Mg(OH)2 and SiO2, a thin film of SiO2 with porous structure were coated on the surface of Mg(OH)2, the contribution rate of BET of the composite caused by SiO2 was 120m2/g.The composite particles modified by the silane coupling agent have a feature of actived index,high specific surface area and good dispersion. Aslo there are chemical bonds between the silane coupling agent and SiO2. Under the condition of silica gel as silica source, Mg(OH)₂/SiO₂ core-shell composite can also be synthesized. High temperatures is preferred. After explained the coating theory and did experimental verification, a theory of adsorption process,"Sol- heterogeneous nucleation- growth-Gel film"was proposed.The pilot experiments on the synthesiz of Mg(OH)₂/SiO₂ core-shell composite is also made. SEM, EDS, FT-IR, BET were used to characterize the chemical composition, morphology, size and superficial crystal structure of the particles. The results show that, there are chemical bonds between Mg(OH)2 and SiO2, a thin film of SiO2 of porous structure was coated on the surface of Mg(OH)2. It is important to make pilot experiments for the further scale-up of this process.On the basis of previous experimental work, alumina hollow structure was prepared with sol-gel method by the use of needle-shaped nano-calcium carbonate and magnesium hydroxide as template. Because it does not exist strong bonding force between alumina nitrate and calcium carbonate, the preparation of alumina tube with alumina nitrate using nano-calcium carbonate as template is not feasible in experimental conditions. The experiments also were done with sodium aluminate as Al source using nano-calcium carbonate as template, and the results showed that there had incomplete tubular structures got in the product, which indicated that there are strong bonding force between sodium aluminate and nano-calcium carbonate. Using the hydrothermal method, we get better products with using sodium aluminate as the source and nano-calcium carbonate as template. And it is necessary to do further experiments to optimize the operation conditions. Using aluminum nitrate as the aluminum source, and magnesium hydroxide as a template by hydrothermal method, hollow sheet structure ofγ-alumina particles was obtained. Using aluminum nitrate as the aluminum source, uniformγ-alumina rod was obtained with the reverse micelles method.