Synthesis Of Mesoporous Silica Nanoparticles And Study Application In Acid-Base Catalysis Reaction

Extensive research efforts have been devoted to synthesize mesoproous materials due to their potential applications in many fields sue as catalysis, adsorptions support for novel metals, and also the design of hybrid materials. Recently, mesoporous silica nanoparticles with dimensions smaller than100nm, also called colloid mesoporous silicas become another hot topic in the community of mesoporous materials due to their short diffusion length, high surface areas and large pore volume. However, the synthesis, collection, surfactant extaction and subsequent surface functionalization remain intellectual challenges. Based on the abundant literature investigations and our preliminary studies on the synthesis of mesoporous porous matreials, in thsis report, a new way was developed to synthesize mesoporous silica nanoparticles with tuned pore shapes and particle size, and its intrinsinic physical and chemical properties were investigated by a combined of characterization techniques, such as X-ray diffraction (XRD), N2adsorption, infrared spectrography (FT-IR), thennogravimetry (TG), Solid state NMR (13C CP MAS NMR and29Si CP MAS NMR) scanning electron microscope (SEM), transmission electron microscope (TEM) and chemical element analysis etc. The main results are listed as follows:I. Using novel surfactant cetyltrimethylammonium tosylate (CTATos) as templates, organic compound triethanolamine (TEAH3) as alkaline source. Under the condition of low surfactant concentration (CTATos:TEOS=0.06:1), Mesoprous silica nanoparticles which can be easily separated by filtration have been successfully synthesized. The synthesis mechanism is deeply studied by changing the type of surfactants, the kind of organic compound amine and the ratio of organic compound amine and tetraethyl orthosilicate (TEOS). The results of high resolving power scanning electron microscope (SEM), transmission electron microscope (TEM) and Nitrogen absorption show that the dimensions of single scattered nanoparticles synthesized are smaller than100nm. The surface area and the pore volume reach770m2/g and0.52cm3/g respectively. In particular, the structural channel completely depends on the ratio of the organic compound and the silica source. The worn-like channel can be accessed under high ratio while the straight trumpet-like type can be accessed when the ratio is lower. In addition, the dispersibility of mesoporous silica nanoparticles shows its strong solvent effect. The Tyndall effect indicated that MSNs can be easily dispersed in protic solvents, such as ethanol and isopropanol, and difficultly in non-protic solvents, such as toluene and cyclohexane.â…¡. Mesoporous silica nanopartilces (MSNs) with large inner surface and outer surface, large pore volume and abundant surface silanol hydroxyl is an excellent supporter. The chapter explored the desperation of organic functionalized molecules in the channel, the surface chemical bonds between the organic molecules and surface silanol hydroxyl and the distribution of surface groups using N-(2-aminoethyl)-3-amino-propylsilyl (AAPMS) as probe molecule with different solvents. The combined characterizations of X-ray diffraction (XRD), N2adsorption, infrared spectrography (FT-IR), thermogravimetry (TG), Solid state NMR (13C CP MAS NMR and29Si CP MAS NMR) and chemical element analysis show that MSNs have higher loading via non-protic solvents (toluene and cyclohexane) after functionalization, which resulted in pore blockage with a lower surface area and pore volume. MSNs have lower loading via protic solvents (ethanol and isopropanol) after functionlaizaton while with a higher surface area and pore volume interestingly. In the meantime, the organic group dispersed in the nanochannel uniformly. Apparently, it is the strong H-bonding between protic solvent and organic groups that prevent the condensation of slilyl reagents, which make the nanoparticles an excellent supporter.III. The functionlization of the inner surface and the outer surface of mesoporous silica nanoparticles is particularly studied by post-grafting technique. By changing the types of organic molecules and their sequences of grafting, the activity effect is related with the type, the size and the acid-base property of organic molecules, with one pot "deacetalization-Knoeveriagel cascade reaction" acting as probe reaction. The combined characterizations of infrared spectrography (FT-IR), thermogravimetry (TG) and Solid state NMR (I3C CP MAS NMR and29Si CP MAS NMR) indicate that different acid groups (R-SO3H) and alkaline groups (R-NH2) can be effectively grafted to the inner surface and the outer surface with the post-grafting technique. The test of activity reaction shows that there is a lower or none reaction activity in the course of employing flexible chain molecules (N-(2-aminoethyl)-3-amino-propylsilyl,-AAP) and there is nearly100%conversion using rigid chain molecules (p-toluidine,-PTA). It indicated that groups with flexible chains will be easily neutralized which largely decreased the reaction activity and that groups with rigid chains can effectively prevent the neutralization so that the catalyzed reaction can take place.