Preparation And Modification Of Mesoporous Silica Based On Hyperbranched Polymer

Mesoporous materials and hyperbranched polymers have attracted increasing attention in chemistry and material science since 1990's. Mesoporous materials have unique structure, such as extremely high surface area, large pore volume, tunable pore size from 2 to 50 nm and versatile possibilities of surface functionalization. Therefore, they have potential application in catalysis, sensors, adsorption and separation. On the other hand, hyperbranched polymers possess some advantages such as low viscosity, good solubility, plentiful of terminal functional groups. Hyperbranched polymers can be prepared easily so that they have emerging application in surface modification, polymer processing, medicine, adsorption and nanotechnology. This dissertation focused on the preparation and modification of mesoporous silica based on hyperbranched polymer, which consisted of three primary parts. The second and third chapters described the preparation of mesoporous silica by the template of amphiphilic hyperbranched polymer self-assemblies. The fourth chapter paid attention to the modification of mesoporous silica with hyperbranched poly(sulfone-amine) and its application in acid dye removal. The fifth chapter concentrated on the preparation of mesoporous silica by the template of poly(sulfone-amine) and its direct simultaneous hypergrafting. The main results and conclusions are described as follows:1. Preparation and characterization of mesoporous silica by the template of poor amphiphilic hyperbranched PEHO-star-PPOAmphiphilic hyperbranched multiarm copolyethers with hydrophobic hyperbranched PEHO cores and linear poor hydrophilic PPO arms were synthesized by cationic ring-opening polymerization. The PEHO-star-PPO is difficult to self-aggregate directly in water due to poor hydrophilicity of PPO arms and hydrophobicity of hyperbranched PEHO cores. Therefore, hyperbranched copolyethers were dissolved in cosolvent and selective solvent for PEHO cores and PPO arms. Mesoporous silica was prepared successfully by the template of PEHO-star-PPO with TEOS as silica source in cosolvent and deoined water. DLS and nitrogen adsorption/desorption isotherms showed that the real structure-directing agent was the self-assemblies of amphiphilic PEHO-star-PPO. As a result, the aggregate size had an important influence on the mesoporous diameter. Three strategies had been used to adjust the mesoporous size: (1) Mesoporous size decreased with increasing of lipophile-hydrophile ratio (the molar ratio of PPO arms to PEHO cores) in the hyperbranched copolyethers template. (2) The volume ratio of selective solvent to cosolvent had great influence on the aggregate size and consequently had effect on the mesoporous size. Mesoporous size increased rapidly with the increasing of water volume ratio in ethanol/methanol and water mixed solvent. (3) The polarity of cosolvent had great effect on the mesopore. When DMSO or acetone as cosolvent, the adsorption/desorption showed H2 hysteresis loop and mesoporous size was small. However, the adsorption/desorption showed H1 hysteresis loop and mesoporous size was much larger with methanol or ethanol as cosolvent.2. Preparation and characterization of mesoporous silica by the template of amphiphilic hyperbranched PEHO-star-PEOAmphiphilic hyperbranched multiarm copolyethers with hydrophobic hyperbranched PEHO cores and linear hydrophilic PEO arms were synthesized by cationic ring-opening polymerization. The PEHO-star-PEO was a typical amphiphilic hyperbranched copolyether and it could form micelles in water. Mesoporous silica was prepared successfully by the template of PEHO-star-PEO with TEOS as silica source. The pore size of as-synthesized mesoporous silica is uneven because of high polydisperse index. Nitrogen adsorption/desorption isotherms showed that the real structure-directing agent was the self-assemblies or unimolecular micelles of amphiphilic PEHO-star-PEO. As a result, the aggregate size had influence on the mesoporous diameter. Three strategies had been used to adjust the mesoporous size: (1) Higher temperature made micelles larger, therefore the pore size increased. (2) Pore-expanding agent, such as trimethylbenzene, could expand the pore size of mesoporous silica. (3) Solvent had effect on pore size of as-synthesized mesoporous silica. When water as solvent, the adsorption/desorption showed H3 hysteresis loop and mesoporous size was large. The real structure-directing agent was the self-assemblies of hyperbranched PEHO-star-PEO. However, the adsorption/desorption showed H2 hysteresis loop and mesoporous size was small with acetone as solvent. The mesoporous size was consistent with unimolecular micelles.3. Modified SBA-15 with hyperbranched poly(sulfone-amine) grafting and its adsorption capacity in acid dye removalMesoporous SBA-15 was synthesized by the template of linear amphiphilic PEO-PPO-PEO. Aminopropyl was anchored, and then hyperbranched poly(sulfone-amine) was grafted onto the SBA-15. The structure and morphology of unmodified and modified mesoporous silica were characterized by FTIR, 29Si CP/MAS NMR, TGA, elemental analysis, XRD, SEM, TEM and nitrogen adsorption/desorption isotherms. Hyperbranched poly(sulfone-amine) grafting did not change the order of mesopore. However, pore size, BET surface area and pore volume were reduced with modification. The adsorption behaviors of Sandolan Red on SBA-15 with and without modification were studied. The maximum adsorption capacity of SBA-15 with hyperbranched poly(sulfone-amine) grafting was 3.3-4.7 times as that of active carbon. The adsorption equilibrium data could be fitted well by the Langmuir adsorption isotherm model. It was then concluded that once a dye molecule occupied a site, no further adsorption could take place at that site and a saturation value was reached which corresponded to the completion of a monolayer. The adsorption process obeyed the pseudo-second-order model, indicating anionic dye had a very strong affinity on SBA-15 with hyperbranched poly(sulfone-amine) grafting. The effect of the experimental parameters, such as grafting content, temperature and solution pH was investigated through a number of batch adsorption experiments. It was found that the removal of acid dye increased with the increase in grafting content of hyperbranched polymer. Temperature and solution pH had effect on the adsorption capacity of Sandolan Red.4. Preparation, characterization and application in dye adsorption of hyperbranched poly(sulfone-amine)/mesoporous silica hybridsPoly(sulfone-amine)/mesoporous silica hybrids and their calcined silica were prepared and characterized. The hybrids had 25.5% poly(sulfone-amine), and the inorganic framework was mesoporous silica with 3.2 nm mesopore. Then, aminopropyltriethoxylsilane was introduced at the same time of hybrid. Hyperbranched poly(sulfone-amine) was grafting onto mesoporous silica with"one-spot"method. The adsorption behaviors of Sandolan Red on modified poly(sulfone-amine)/silica hybrids were studied. Their maximum adsorption capacity of Sandolan Red was 3 times as that of active carbon.