Design And Synthesis Of New Mesoporous Materials And Their Function

Mesoporous materials are a kind of porous inorganic materials with the pore size between 2 - 50 nm, which can be applied in the fields of catalysis, adsorption, sensor, etc., due to their highly ordered pore structures and very large specific surface area. Up to date, various researchers have synthesized more and more mesoporous materials with different compositions, meso-structures, novel properties by the supermolecule assembly concept. The applications are based on the properties. We might obtain the aimed functional materials, only when the synthesis or its mechanism was in control. Thus it can be seen that to understand accurately the synthesis process and to design the aimed novel materials are the main tasks in this field in the future.This thesis is divided into two major parts: (i) mechanisms - the influence of the reaction conditions and a hard spheres packing mechanism; (ii) designable synthesisa kind of nano-sized silica hollow spheres and their biomedical applications.By our understandings of the formation mechanism of the mesoporous materials, by soft-templated assembly, the electric matching effect between the soft-templating agents and the inorganic species is very crucial. Most researchers consider that the templating mechanism of the non-ionic templating agents is also the electric matching effect. However, it is not very similar with that of the cationic templating agents, the nonionic surfactants and the inorganic species are interacting by the "ionic bridge" (-EOH⁺)(X^-)(H₂⁺OSi-). As the bridge, the inorganic anions play a very important role in the system. And the ions, especially the anions, affect the micelles' hydrophilic/hydrophobic properties and change the meso-structures effectively. To have a systemic view on the ionic effect is much important and valuable. We employed a very "sensitive balance" (KIT-6 system), and improved it by finely adjusting the acidity, to compare the ionic effect (meso-structure transformation from Ia3d to p6m) of the popular ions (Cl^-, Br^-, NO3^-, and HSO₄^-). We consider that, the surfactant micelles' hydrophilic/hydrophobic properties in the acidic condition are the result of the two contrary effects: dehydration effect and radii effect. By the interaction of the two different effects, we find and report the sequence in the synthesis condition: SO₄^2- (HSO₄^-) > NO₃^-> Br^-> Cl^-. Maybe the SO₄^2- (HSO₄^-) anion has a much stronger dehydration effect, it seems to be the most hydrophobic. The other three have the similar dehydration effect, so their hydrophilic/hydrophobic properties are mainly determined by their radii effects. However, the radii effect is weaker than the dehydration effect, so we have to compare them by a finely adjusted "sensitive balance". By this method, we have determined the hydrophilic/hydrophobic sequence in the self-assembly condition, which is quite valuable for the meso-structure controlling and our further researches.Since the mesoporous materials was invented, the mechanisms are always the hotspot for the researchers. Up to now, the interaction of the inorganic species and the surfactant templating agents are determined to cause the self-assembly in the aqueous solution system. In the soft-templating system, the LCT (Liquid crystal template) and the CSA (Cooperative self-assembly) are representative of the mechanisms.Icosahedral (ICO) crystals are very charming due to its unusual 5-fold symmetry, and some researchers discovered that ICO is also a stable status for the packing of a small quantities of solid particles. We have concluded a new kind of mechanism - Hard spheres packing (HSP) by our experiments, and we detailedly discussed it and proved it to be truth. Furthermore, the ICO mesoporous materials with 5-fold symmetry of both the macro-scale and the meso-scale have been found and reported. In our view on it, our proposed HSP mechanism is different from the well accepted LCT and CSA formation mechanisms. To be simple, the LCT is an "assembly before condensation" process and the CSA is an "assembly during condensation" process. In either the CSA or the LCT mechanism the micelles are embedded in the final liquid crystal phase with the inorganic species as the continuous phase, which generally leads to monomodal mesopores after the surfactants are removed. In contrast, the HSP pathway is an "assembly after condensation" process.By our understanding of the HSP, we controlled the conditions and obtained a kind of mono-dispersed composite micelles. And the composite micelles can be dispersed to be sol, due to their size is similar to the surfactant micelles'. DMDMS is employed to prevent the inter-particle aggregations. The nano-sized silica particles, with the biocompatible silica shells, are < 30 nm and can facilitate the endocytosis of the living cell's plasma membrane. A kind of nano-sized silica hollow spherical particles can be obtained, by removing the surfactant cores from the composite micelles. And the hollow cores can be fully impregnated with the antibacterial Ag or the bioactive Pt, etc., to form the nano-sized cores with the protective silica shells. And it is proved that the nano-sized silica hollow spherical particles are well biocompatible by the FITC-loaded nano-particles' penetrating the living cell's plasma membrane. The nano-sized silica hollow spherical particles may be a new kind of wonderful and valuable materials in applications, owing to its large cage (-13 nm) for delivery; its micropores in the shell for release; its modifiable shell for special functionalizations.