Synthesis And Enzyme Immobilization Of Mesoporous Silica And Mesoporous Carbon

Mesoporous materials have attracted great attention in enzyme immobilization dueto their high specific surface area, pore volume and tunable pore size. In contrast tothe extensive investigation on the preparation and characterization of mesoporoussilica, less attention has been paid, to the best of our knowledge, to the systematicapplication in enzyme immobilization. Mesoporous carbon materials are of greatinterest owning to the advantage of high mechanical strength, chemical resistance andelectroconductibility. Magnetic mesoporous carbon with cobalt nanoparticles confinedin pore channels can act as adsorbent of enzyme because of the easy separation andcontrolled placement realized by means of an external magnetic field. This thesisfocuses on the synthesis of mesoporous silica and mesoporus carbon materials andtheir application in enzyme immobilization. Afacile “one-pot” strategy was utilized toprepare magnetic mesostructured Co/ordered mesoporous carbon(OMC). Theobtained mesoporous materials with different pore size were used to immobilizeenzyme with various size. The adsorption behavior of enzyme and the catalyticactivity of immobilized enzyme were also investigated. This thesis includes thefollowing sections.Mesoporous silica with various pore sizewas synthesized using triblock copolymerP123as template tetraethyl orthosilicate(TEOS) as precursor andtrimethylbenzene(TMB) as swelling agent at various synthesis temperatures andunder different stir conditions. With the increase of temperature from100℃to200℃,the pore size of mesoporus silica increases gradually, reaching the largest porediameter of29.20nm at200℃. Disordered mesocellular silica foam with a high porevolume of1.57cm3/g and a large pore size of21.63nm was obtained by the addition ofTMB. The shrinkage of stir time does not affect the mesostructure except that the poresize reduces to7.6nm. Laccases immobilized on mesoporous silica with a pore size of7.6nm exhibit higher stability than those on other samples due to the matching ofenzyme size and pore diameter. The mesoporous silica was also used as hard templateto prepare ordered mesoporous carbon and the obtained materials were applied toimmobilize lysozyme. The adsorption amount of lysozyme reaches the largest valueat a pH of11. The adsorption process can be described by the Langmuir isotherm andpseudo-second-order kinetic. Mesoporous silica/carbon composite materials were prepared under acidicconditions by using resorcinol/formaldehyde as carbon precursor, TEOS as silicaprecursor and F127as template. Mesoporous carbon with a high specific surface areaof602m2/gand a pore volume of0.58cm3/gcan be obtained by dissolving silica inNaOH solution at80℃. The adsorption process of lysozyme immobilized onmesoporous carbon can be described by the Freundlich isotherm andpseudo-first-order kinetic. The increase of calcination temperature leads to an increaseof the amount of micropore volume and an evolution from micropores to mesopores,resulting in an increase of surface area and pore volume, but mesoporous carbonshould be used below450℃.The adsorption of lysozyme on carbon materialscalcined at different temperatures can be described by the Langmuir isotherm andpseudo-second-order kinetic.Mesoporous carbons have been rapidly synthesized using an aqueous strategy bythe polymerization of phloroglucinol and formaldehyde in the presence of triblockcopolymer F127under acidic conditions. The synthesis temperatures and theconcentrations of hydrochloric acid play an important role in the formation of the porestructure of mesoporous carbon. The pore size decreases with increasing synthesistemperatures, reaching7.6nm with the maximum surface area and pore volume at40℃. With the concentration ofhydrochloric acid increasing from0.5mol/L to2.5mol/L, the pore size of mesoporous carbon decreases from7.6nm to5.6nm, thesurface area from788to691m2/g, and the pore volume from0.38to0.25cm3/g.Mesoporous carbon was used to immobilize Horseradish Peroxidase(HRP). Theresults show that immobilized HRP remains intact and the thermal stability, pHstability and storage stability of immobilized HRP have been improved significantlyin comparison with free HRP. The immobilized HRP retain more than50%relativeactivity after recycling for6times.A facile “one-pot” strategy was used to synthesize a mesostructured magneticCo/ordered mesoporous carbon(OMC) composite associated with a directcarbonization process from resol, cobalt oxalate and triblock copolymer F127.When the content of Co is0.02, the specific surface area and pore volume ofmagnetic mesoporous carbon increase from552m2/g and0.40cm3/g to621m2/g and0.48cm3/g, respectively, compared to the mesoporous carbon without Co,but the surface area and pore volume tend to decrease gradually with furtherincrease of Co content. The saturation magnetization(Ms), remanent magnetization(Mr) and coercive force(Hc) can be adjusted by varying the Cocontent. The low Ms, Mr and Ms/Mr indicate the ferromagnetism property ofmesoporous carbon. The prepared magnetic mesoporus carbon was used toimmobilize microperoxidome MP-11. The adsorption of MP-11can bedescribed by the Freundlich isotherm and comply with pseudo-second-order kinetic.The thermal stability, pH stability and storage stability of immobilized enzyme havebeen improved significantly in comparison with free MP-11. The immobilized MP-11retains more than60%relative activity after recycling for10times.