Synthesis And Characterization Of Mesoporous Silica By Using Anionic Surfactant As Template

Following a recommendation by IUPAC, mesoporous materials are the materials with a pore diameter between2-50nm. Mesoporous materials with high surface area and pore volume, ordered mesopores, tunable pore distribution, and superior surface features, which made it play an important role in macromolecular adsorption and separation, drug storage and transportation, especially in catalytic reaction. Surface functionalization of mesoporous silica is especially meaningful, which can combine the functionality of organic groups and thermal stability and robustness of the mesoporous silica skeleton. Functionalized mesoporous materials, will have greater functionality when it has greater amount of functional group. Ordered3D cubic mesoporous silicas are highly interesting and would be more advantageous than those with uni-dimensional mesopores, due to the lower resistance to pore blocking and easier diffusion of the molecules in the pore channels. In addition, it is still a challenge to expand the synthesis routes of mesoporous materials.In this paper, the main targets are development of synthesis route of anionic surfactant template system and synthesis of multi-amine-functionalized3D channel structure mesoporous silica and study its application in adsorption and catalysis. There are three main parts in this thesis.1. Synthesis and formation mechanism of multi-amine-functionalized cubic mesoporous silicaHerein, we report the synthesis of multi-amine-functionalized cubic Fd-3m mesoporous silica by using anionic surfactant N-lauroylsarcosine sodium (Sar-Na) as the template,[3-(2-aminoethyl)aminopropyl]trimethoxysilane (DAPS) or3-[2-(2-aminoethylamino)-ethylamino]propyltrimethoxysilane (TAPS) as the CSDA. Transition of mesophase from low-curvature2D hexagonal P6mm to high-curvature3D cubic Fd-3m was observed when DAPS or TAPS replaces APS as the CSDA in anionic surfactant templated system. To our knowledge, this is the first time the tuning of the mesophase by using DAPS and TAPS as the CSDA in the anionic surfactant templated system has been reported. The effect of the CSDA in these experimental conditions was examined and explained that due to the size of DAPS or TAPS being larger than the size of APS, the steric effect would increase the effective interfacial area of the head group of the surfactant, and then the packing parameter (g) would be reduced and therefore a cage type cubic mesophase was favored. After extraction of the anionic surfactant template by ethanol solution with ethanolamine, multi-amine-functionalized3D cubic Fd-3m mesoporous silica was obtained.In addition, we synthesize the cubic Ia-3d mesostructured silica by using N-lauroylsarcosine sodium (Sar-Na) as the template and3-aminopropyltrimethoxysilane (APS) as the CSDA under the aid of acetate. The phase transformation from the2D hexagonal P6mm to the bicontinuous3D cubic la-3d was occurred through the addition of a proper amount of acetate. Furthermore,[3-(2-aminoethyl)-aminopropyl]trimethoxysilane (DAPS) was also used as the CSDA to synthesize1Ia-3d mesostructured silica under the aid of sodium acetate. In the presence of the acetate, the hydrophilic carboxyl group could reside inside the micelle of anionic surfactant Sar-Na and electrostatically interacted with APS. This would reduce the negative charge density of the anionic surfactant in the micelle and thus weaken the repulsive interaction between the head groups of the anionic surfactant. This would lead to decrease in the effective head group area ao, thus the surfactant packing parameter g increased and the resultant mesophase of the silica exhibited a lower interface curvature. After extraction of the anionic surfactants, amino and di-amine functionalized3D bicontinuous cubic Ia-3d mesoporous silicas were obtained.2. The applications of multi-amine-functionalized mesoporous silicaThe amino functionalized mesoporous silica has potential applications in adsorption and supports for metal nanoparticles. After extraction of the anionic surfactant template, multi-amine-functionalized mesoporous silica was obtained. The functionalized mesoporous silicas has great application potential in adsorption and remove the heavy metal ions, and load of noble metal nanoparticles, due to orderly three-dimensional channel structure and the high amino group content. In this paper, the amino functionalized mesoporous silicas were used as adsorbents to absorb metal ions and as support to immobilize noble metal nanoparticles. We used multi-amine-functionalized mesoporous silica as the support to prepare the catalyst and tested the catalytic activity by reduction of4-nitrophenol and hydrogenation of allyl alcohol.3. Synergy between polyamine and anionic surfactant:a bioinspired approach for ordered mesoporous silicaInspired by the effect of the electrostatic supramolecular selfassembly of silaffins (or polyamines) with the polyanions, here we report a novel bioinspired approach to synthesize mesoporous silica by using an anionic surfactant as a template. Because of the electrostatic self-assembly between the cationic polyamine and anionic surfactant, the organic complex colloid mesophase was formed and served as a template in which the anionic micelles were covered with cationic polyamine chains, which were meanwhile gathered by the accumulated anionic micelles. With the help of cationic polyamine, anionic surfactant micelles could be utilized as a mesostructure template whereas with the aid of the anionic surfactant micelles the cationic polyamine chains underwent aggregation to possess the ability to induce silica condensation. The charge of Sar-Na could be tuned at different pH values, and this would influence the aggregated packing mesophase of the Sar-PAC complexes, giving rise to different mesostructure of the as-synthesized silica. In addition, the amount of cationic polyelectrolyte also has an important influence on the products mesostructure. Performing in a bioinspired fashion under mild conditions and without using any organosilanes, this approach could not only shed light on the study of biosilicification but also serve as a general method for the anionic-surfactant-templated mesoporous materials.