Study On Preparation Of Vesiclular Silica And Its Immobilization Of Lipase

Vesicular silicas named VS-0and VS-1were prepared by utilizing cationicsurfactant cetyltrimethylammonium bromide （CTAB） and anionic surfactant sodiumdodecyl sulfate （SDS） as a dual-template, tetraethoxysilane （TEOS） as silica sourceand different amount （TIPB:SDS=n:1, n=0,1） of1,3,5-triisopropylbenzene （TIPB）was added into this mixture as the micelle expander via hydrothermal process. Theformed materials were characterized by Fourier transform infrared spectroscopy（FT-IR）, transmission electron microscopy （TEM）, N₂adsorption-desorption and fieldemission scanning electron microscopy （FESEM）. The results indicated that bothVS-0and VS-1were unilamellar and multilamellar vesicular silicas, the pore structureparameters of these samples were described as follows: the average pore diameterwere15.24nm and20.51nm; the specific surface areas were314m²g^–1and362m²g^–1; the pore volumes were0.92cm³g^–1and1.45cm³g^–1. Possible mechanism for theformation of VS-1was proposed, which proved that the addition of TIPB was one ofthe effective ways in controlling the pore size of vesicular silicas. The VS-0and VS-1were used as supports for immobilization of Candida rugosa lipase （CRL） and theenzymatic activities of CRL and immobilized CRL were compared by hydrolysis oftriacetin. VS-1-CRL showed higher loading amount and greater catalytic activitycomparing with VS-0-CRL; In addition, immobilized CRL exhibited an excellentadaptability in a wider pH region and higher temperature: the optimal pH andtemperature of the hydrolysis of triacetin for CRL were7.0and35°C, while theoptimal pH and temperature of VS-0-CRL and VS-1-CRL were8.0and50°C,60°C.Immobilized CRL had better thermal stability and reusability compared with freeCRL: the VS-0-CRL and VS-1-CRL still maintained46.91%and53.22%of theirinitial activities for incubating2.5h at60°C, while CRL only retained41.86%of itsoriginal activity for incubating1.5h. The relative activity of VS-1-CRL maintained at33.92%of its original activity while the relative activity was25.74%for VS-0-CRLafter6reuses. It was proved that VS-1-CRL exhibited the best reusability.In acidic condition, vesicular silicas denoted as VS-0.6and VS-1.72withdifferent pore diameters were synthesized using triblock copolymer P123and anionicsurfactant sodium dodecyl sulfate （SDS） as a co-template, TIPB as an additive atdifferent molar ratios （SDS:P123=n:1, n=0.6and1.72） of P123:SDS by hydrothermal process. SAXRD, FESEM, TEM, N2adsorption-desorption and FT-IRmeasurements demonstrated that pore volumes and pore diameters were decreasedand surface areas were increased with the increase of molar ratio （SDS:P123）. TheVS-0.6and VS-1.72were used as carriers to immobilize CRL. When these sampleswere adsorbed for6h in CRL phosphate buffer （pH7.0） solution, immobilized lipaseVS-1.72（431.57mg g–¹ï¼‰ showed higher loading amount of CRL comparing withVS-0.6（384.69mg g^–1）. The optimal pH and temperature of VS-0.6-CRL andVS-1.72-CRL （pH=8.0、T=50°C） was shifted compared with the optimum reactioncondition of CRL （pH=7.0、T=35°C）. The results demonstrated that immobilizedCRL had an excellent adaptability in a wider pH region and higher temperature, betterstability and reusability compared with CRL, especially the VS-1.72-CRL was thebest, VS-1.72-CRL still retained52%of its initial activity for incubating2.5h at60°C and its relative activity was34%of the initial activity after the sixth reuse.Mesoporous silicas （MS-0.5（CTAB:P123=0.5:1）, MS-1（CTAB:P123=1:1））with hexagonal and vesicular mesoscopic structure were prepared by hydrothermalmethod employing P123and CTAB as a dual-template with the existing of sameexpanding agent and silicon source. TEM image illustrated that two samples hadhexagonal arrangement of parallel channels and layer arrangement of multilamellarvesicle structure, and contained a non-uniform pore size distribution of mesoporousand macroporous. The immobilization of CRL on these materials through physicaladsorption was studied. The result of N2adsorption-desorption showed the lipasemolecules had been adsorbed into the channels of the carriers and the loading amountwas decreased following the order of MS-1（412.13mg g^–1） and MS-0.5（381.58mgg^–1）. The effects of pH and temperature on enzyme activity of free lipase andimmobilized lipase were investigated. The results showed that the immobilized lipasehad better resistance of alkali and temperature. The relative activity of immobilizedlipases decreased with the increase of the reuse times, but the activity of MS-0.5-CRLdecreased rapidly. The relative activity of MS-1-CRL with better reusabilitymaintained28%of its original activity while the relative activity was only25%forMS-0.5-CRL after6reuses.