Study Immobilized Cellulase On Ferrite And Its Composite

Cellulase is a key biocatalyst enzyme, which hydrolyzes cellulosic crystals to produce glucose. It’s widely used in many fields such as food industry, protecting environment and energy. However, there are some limitations about the application of free cellulase, because of its inefficient utilization and easy deactivation. There are many advantages on immobilized enzyme, for example, easily separated and recovered, repeated use, so it’s possible to improve utilization efficiency of free cellulase and its industrial application.In this thesis, we prepared spinel ferrite composites NiFe2O4-SiO2via ethanol-water heating and supercritical fluid drying. The monodispersed spinel ferrite ZnFe2O4was syhtnesized by solvothermal method. Magnetic immobilized cellulase were prepared by the crosslinkage method using NiFe2O4-SiO2and ZnFe2O4as carriers. The contents were as follows:1. Preparation of carriers:The spinel ferrite composites NiFe2O4-SiO2were formed by the precursor prepared via the ethanol-water heating at the condition of pH=7.5,60℃and alcohol-water ratio5:1, aerogels using supercritical fluid drying (SCFD) technology at270℃,8MPa. The monodispersed spinel ferrite ZnFe2O4was syhtnesized at180℃for24h by solvothermal method with ethylene glycol as solvent and KAc as agent.2. Immobilized cellulose:Cellulose was immobilized on NiFe2O4-SiO2, ZnFe2O4with glutaraldehyde as crosslinking agent. The binding of magnetic nanoparticles and cellulose is confirmed by Fourier Transform Infrared Spectroscopy(FT-IR). In the given conditions the cellulase hydrolyzes carboxymethyl cellulose sodium to produce glucose, then the absorbance value was measured by DNS spectrophotometry at540nm to calculate the activity of immobilized cellulase. The result shows that when the NiFe2O4-SiO2as carriers the optimal conditions of immobilization was mass fraction of glutaraldehyde5%and cellulase concentration of4mg/mL at20℃,pH4.8for5h; when the ZnFe2O4as carriers the optimal conditions of immobilization was at40℃and keeping other conditions same.3. studying properties of cellulase:studying on enzymatic properties of free cellulase and immobilized cellulase. Compared to free cellulase, the optimal pH of immobilized cellulase shifted from pH4.8to4.2, the optimal temperature was increased and thermal stability of the immobilized cellulase enhanced greatly. As a result of this immobilization. the relative activity was maintained more than70%when the immobilized cellulase at70℃for4h, that was only16.94%when the free cellulase at70℃for2h.