Research On Synthesis And Controlled Release Of Hollow Mesopores Materials

Materials constitute the substantial basis of human social life, and its development contributes to the transition of times, hence advancement of human material civilization and society as a whole. Nowadays, material, along with energy and information, supports the modern science and technology. Now material , important foundation of revolution of modern technology, provides essential condition for exploitation of new energy, space technology, and micro-electron technology. Hollow spherical mesoporous material, a new material, possess such characteristics as good surface permeability, low density, and high mechanical stability. In recent years, synthesis of hollow spherical mesoporous materials, through various approaches, has become the frontier and focus of material chemistry research. There appeared a lot of reports in such famous journals periodicals as "Science","Nature","Advanced Materials"and"Chemistry of materials". In particular, application of hollow spherical mesoporous material has been increasingly attracting attention.Inorganic material of hollow spheres, has been utilized widely, such as catalyst, adsorbent, optical fiber, acoustic insulator, artificial battery, drugs delivery, and protection of biologically active agent, and controlled release capsules of various substances. Mesoporous materials, esp. orderly ones, with its application to catalysts, low-dielectric coatings and optical materials, and as molds for new material synthesis, has made itself the focus of material research. Therefore, by simpler and easier methods, combining the advantages of inorganic hollow spherical materials, binary and polybasic composite oxides, with mesoporous structure is significant in the research of material chemistry, also a challenge in material synthesis.Usually, preparing hollow sphere involves molds method, whose synthesis process is complex and experiment index is hard to control.In order to achieve high controllability of release in application, the surface of the material is frequently modified. But most inorganic spheres with hollow structure have less silanol groups after removal of the templates or organic components by calcination because of condensation of silanols group at high temperature, which is unfavorable to further modification of material. Here we present a facile route for preparing solid SiO₂/ Al₂O₃ spheres by using TEOS and aluminum nitrate as silica and alumina sources, in which we combine a sol-gel process with an O/W/O microemulsion.In filter process, hollow spheres are formed by means of boiling water. Although the hollow spheres show somewhat distorted shape the intact hollow structure and mesopores in the shell wall are still obvious. More importantly, a large amount of silanol groups are retained for the absence of calcinations, which offers an opportunity to modify material further, broaden application of material. In this experiment, PEG is introduced as an additive , when the self-assembly process is going, a large amount of uniform mesopores are formed in the shell wall. A series of characterization results show that the particle size of the hollow spheres and pore size of mesopores in the shell wall can be controlled by such factors as emulsion temperature, stirring speed, average molecular weight of PEG, the amount of HNO₃ and Al(NO₃)₃in the precursors, and the oil phse.The particle size of hollow spheres increase along with the increase of stirring speed, and the pore size of mesopores in the shell wall increase along with the increase of average molecular weight of PEG. The sol viscosity is found to have a significant influence on the perfect formation of hollow spheres. The purpose of synthesis of material is to apply it. More and more attention is paid to application of hollow spheres to controlled release. To obtain hollow spheres with ordered mesopores in the shell wall, we present a novel route for combining sol-gel process and O/W microemulsion with hydrothermal technique. We successfully synthesize hollow SiO₂ spheres with ordered mesopores in the shell wall by using CTAB as template. A series of characterization results indicate the sample has cubic symmetry structure. Furthermore the hollow SiO₂ spheres is intended to carry avermectin drug as controlled release carrier. Results show that the hollow SiO₂ spheres have a strong ability to adsorb avermectin,which can elevate the drug adsorption rate greatly with a 68 percent drug-carrying rate. The adsorption, a physical process, does not convert the property. The release span of avermectin controlled release agent lasts more than 28 days in solution medium by continuously stirring, which shows that the new hollow SiO₂ controlled release agent with a good release effect can prolong the effective time of drug. Therefore it is expected to an ideal controlled release carrier of new generation for farm insecticide.