Mesoporous Silica: Synthesis, Morphology Control, Assembly, And Property

Mesoporous materials have been obtained by means of the corporative interaction between inorganic precursors and supra-molecular surfactants through sol-gel process. The unique structure such as extremely high surface area (up to 1000 m²/g), large adjustable pore size (2-50nm), uniform pore arrangement, and narrow pore size distribution have made such materials the focus of great interesting. They could have potential usage in various areas especially as adsorption and separation, ion exchange, catalysis, molecular host, optoelectronic, photo devices, sensing, drug delivery, which have been the focus of the research in the condensed matter physics, chemistry and materials fields since the first discovery of M41S family in 1992. In this paper, the synthesis, morphology control, assembly and property of mesoporous materials have been studied.From the fundamental aspect, the synthesis and morphology control of mesoporous SBA-16 have been investigated.The cubic phase mesoporous materials SBA-16 possess 3-D channel connectivity, SBA-16 is considered to be suitable than SBA-15 in mass transportation process for applications in catalytic and separation technologies. However, compared with SBA-15, limited research papers were published in the application of SBA-16. This is due to the difficulty in the synthesis of the SBA-16 material. It is important to develop the easy synthesis route of the SBA-16 material for its further applications. In this paper, we systematic studied the formation of SBA-16 mesophase. The results show that SBA-16 could be obtained in a molecular ratio of 1TEOS: (2.5-7.5) HCl: (0.002-0.005) F127: (90-220) H₂O at 24-34℃. Moreover, the quality of the SBA-16 can be monitored by the time of the deposition formation.Accompany with the investigation of the formation of the mesophase, the morphology of the SBA-16 have also been controlled. We present a simple synthesis of SBA-16 crystals under static without any salt additives or auxiliary solvent by carefully control of the reaction temperature and reactants ratio. By this simplified synthesis approach, crystal like mesoporous silica SBA-16 with novel decaoctahedronand rhomb-dodecahedron shape, as well as sphere like SBA-16 is obtained. This work show a diversity of single crystal like morphologies which were observed earlier by others. We extended the morphology diversity from ionic template synthetic route to non-ionic tri-block copolymer template route. The formation of SBA-16 with different shapes could be explained by a combination of cooperative templating model for meoporous silica synthesis, corona with hard core model for colloidal like inorganic-organic hybrid and maximizing entropy by minimizing area model for colloidal phase self-organization.From the potential application aspect, assembly of heteropoly acid (HPA) or Fe oxides into mesoporous materials and their property have been explored.The silica surface was first functionalized with an amine ligand and then treated with HPAs. The amines reacted with HPA to result salt (NH3HPA) whose bonds are far strong than hydrogen bonds between silanol group and HPAs, by this chemically bonding, the HPAs were held to the silica surface. Heteropoly acid of Keggin structure tungstovanadogermanic (HsGeWnVO^) has been chemically anchored to the modified SBA-15 surface. The material was characterized by various techs to verify cluster attachment and the structure of the HPA on the support. On the basis of the spectroscopic evidence, HPA clusters were attached firmly to the surface. This material could be useful as heterogeneous catalyst.Instead of the chemically binding of HPA into the channel of the mesoporous materials, the HPA (H5GeWnV04o, H5GeMoWioV04o) have also been physically adsorption onto the surface of mesoporous MCM-41, MCM-48, SBA-15, SBA-16. The material was characterized by IR and XRD to confirm the existence of mesopore and Keggin structure. The results show the dispersion state of HPA is strongly depend on the MPS type. The protonic conductivity of the HPA/MPS materials has also been measured. We could conclude that the conductivity of the HPA/MPS materials are determined by the dispersion state of HPA based the results: SBA-15>SBA-16 >MCM-41>MCM⁴8. Moreover, by carefully control of the molecular ratio of HPA and MPS, the conductivity of HPA/MPS could sometime higher than HPA itself.Beside the HPA, the Fe oxides have also been used as guest materials in the hostmesoporous materials. The Fex0y/SBA-15 mesoporous molecular sieves have been prepared by pH-adjusting method and used as the catalysts for CVD growth of carbon nanotubes. The results show the carbon nanotubes grow outside of the pore of the mesoporous Fex0?/SBA-15 mesoporous molecular sieve. The straighter, uniformed and open carbon nanotubes with the higher degree of graphitization could be obtained, which is different to results from others. The diameter of carbon nanotubes will be large with the increase of the Fe content in the SBA-15 mesoporous molecular sieve.Heteropoly acids are referred as 'supper solid acid'. As an extending study of their catalysis and protonic conductivity property, the usage of HPA as photo catalyst has also been studied. A series of titanium dioxide materials composited with Keggin type HPA [Xn+W,204o](8'n) (XW12; Xn+=P5+, Si4+, Ge4+) were prepared by sol-gel method. The prepared composites showed higher photocatalytic activity as a photocatalyst for X-3B degradation than pure TiC>2, pure HPA or mechanically mixture of TiC>2 and HPA. Among the three HPA-TiO2 hybrid materials, the reactivity is as follows: PW12 > SiV/12 > GeV/12. For the same POMs with different weight loading, the reactivity followed the order: 30 wt % > 15 wt % > 45 wt %.