Synthesis, Functionalization And Application Of Mesoporous Silica Materials

Silica-based mesoporous materials possess high surface area, large pore volume,steady framework, easy modified internal surface and defined pore structure. Theyalso have many other advantages, such as high thermal and mechanical stability, lowreactivity and non-toxicity. Since the first synthesis of mesoporous material ofMCM-41in1992by American Mobil Company, mesoporous materials have been theresearch focus in many fields and have found wide applications in catalysis, heavymetal adsorption, biological molecules immobilization and drug delivery. Silica-basedmesoporous materials contain plenty of hydroxyl groups; the interaction with guestmolecules is the driving force to hold the guest molecules being in the pores of thematerial. However, only hydroxyl at the surface is not enough for immobilizingvarious molecules due to the diversity of guest molecules. In order to extend theapplication fields, the surface modification of mesoporous materials is very necessary.The grafting of organic functional groups such as amino, sulfhydryl and alkyl, wouldnot only increase the species of active groups on the surface of mesoporous materials,but also enhance the surface character and reactivity of materials. This modificationcould be a platform for further adding other functional groups to the mesoporousmaterials.Mesostructure cellular foam （MCF） is a new-type materials which have thebiggest pore sizes of the existing mesoporous materials. The large spherical cells areinterconnected by windows, holding a narrow pore size distribution. It possesses openpore structure with other features such as easy synthesis and good thermo-stability.MCF has the prodigious superiority and has been used for catalysis carrier,immobilization of large biological molecules and controlled drug delivery. In thisresearch work, a series of functionalized MCF materials were synthesized via graftingorganic functional groups on the surface of MCF. The resulting MCF materials weresuccessfully used for the adsorption and release of drug molecules and the separationof chiral drugs. The following are the detailed results:First, we synthesized MCF materials using P123as surfactant template. （3-aminopropyl） triethoxysilane （APTES） and2,3-epoxypropoxy propyltrimeth-oxysilicane （GPTES） were used to modify MCF to obtain NH₂-MCF andEpoxy-MCF. We then use glucose and glutaral to decorate NH₂-MCF, andβ-cyclodextrin （β-CD） to modify Epoxy-MCF. The resulting modified MCF materialswere obtained: G-NH₂-MCF, CHO-NH₂-MCF and β-CD-MCF. We also preparedaklyl-G-MCF and L-Try-CD-MCF materials by using trmethoxy（octadecyl）silane tomodify G-NH₂-MCF and L-tryptophan to decorate β-CD-MCF. All obtainedmesoporous materials were characterized by FTIR, XRD, TEM and N₂adsorption-desorption. The results demonstrate that the active groups weresuccessfully grafted on the surface of pores. The functionalization did not affect thefeature of mesoporous materials but slightly change the degree of the structure order.The adsorption and release profile of streptomycin sulphate from the abovemesoporous materials including MCF，NH₂-MCF，G-NH₂-MCF，CHO-NH₂-MCFand Aklyl-G-MCF were studied in detail. The results indicated that the adsorptionamounts of streptomycin sulphate on modified mesoporous materials were muchhigher than that on pure MCF materials. It was indicated that the adsorption propertyof mesoporous materials was significantly improved by the functionalization and therelease rate of streptomycin sulphate become slow. The release profile of streptomycinsulphate on G-NH₂-MCF and Aklyl-G-MCF indicated that both hydrophilic andhydrophobic groups slowed the release rate of drug. The release profile ofCHO-NH₂-MCF further revealed that the release rate of drugs have a prodigiouschange upon pH change. The release rate was much faster in lower pHs due to that theSchiff-base interaction between drug and surface became unstable under the acidicconditions.We also investigated the separation of L-and D-glutamic acid using modifiedmesoporous materials including β-CD-MCF and L-Try-CD-MCF. The resultsindicated that the modified mesoporous materials were effective for chiral separationof L-and D-glutamic acid and L-Try-CD-MCF had a better performance thanβ-CD-MCF. The results conclude that chiral molecule modified mesoporous materialshave obvious superiority and prospect to the separation of chiral molecules. In Summary, we have synthetized a series of functionalized MCF materialswhich greatly expand the variety of mesoporous materials. This research providesefficient way for the functionalization of mesoporous materials and enlarging theapplication of mesoporous materials. Some kinds of the modified mesoporousmaterials possess good capacity to control the loading and release of drugs, whichmight be suitable for long-term drug dosage. The other β-CD modified mesoporousmaterials have effect on the separation of chiral molecules such as L-and D-glutamicacids. Our future work will focus on optimizing the separation via changingexperimental condition and functional groups.