Preparation And Characterization Of Alginate/SiO₂ Hybrid Hydrogel For Immobilization Of Cellulase

In this study, two kinds of hybrid composites were prepared using sodium alginate as polymer moiety, silica as inorganic moiety. Both of the hybrid composites were studied as carriers for immobilization of cellulase. In detail, the thesis includes the following parts:PartⅠ: Fabrication and characterization of a novel covalent cross-linked alginate/SiO2 hybrid hydrogelThe first novel hybrid composite derived from 3-aminopropyltrimethoxysilane and sodium alginate was prepared through covalent cross-linking reaction accompanied with a hydrolysis/condensation single reaction in a reaction system (The hybrid composites were designed as covalent cross-linking Alg-SiO2). The characterization of covalent cross-linking Alg-SiO2 was employed by FT-IR ,SEM and EDS etc. The results revealed that cross-linking reaction was carried out by -NH2 and COO-.The shear modulus (G), the molecular weight between cross-links (Mc), and degree of swelling (Q) of the hydrogel were also investigated. The results of this study showed that the proterties of hydrogel would be strong affected by its structure. Our work may be as a mean to generate hybrid hydrogels with a range of mechanical properties.PartⅡ: Alginate/SiO2 hybrid hydrogel for cellulose immobilization In order to reveal the potential applications of the novel hybrid hydrogel, the covalent cross-linking Alg-SiO2 hybrid hydrogel was used as carriers for immobilization of cellulase. The loading efficiency of immobilized cellulase was up to 86% and the SEM photographs showed that the cellulase was trapped in carriers homogeneously. The activities of free cellulase and immobilized cellulase were determined by measuring the amount of glucose made from carboxymethyl cellulase in the given conditions. The results showed that the immobilized cellulase had a higher Km than free cellulase. The immobilized cellulase had better stability with respect to pH or temperature than free cellulase and it also remained up to 50% activity after 10 cycles.PartⅢ: Immobilization of cellulase based on Sol- Gel process 3-aminopropyltrimethoxysilane derived gel was incorporated into sodium alginate and enzyme solution, followed by Ca2+ cross-linking(The hybrid composites were designed as Sol- Gel-derived Alg-SiO2). The effects of pH, temperature, Michaelis–Menten constant (Km), storage and thermal stability on the two immobilized cellulases activity were examined. The covalent cross-linking Alg-SiO2 immobilized cellulase had more loading efficiency (86%) than the Sol- Gel Alg-SiO2 immobilized cellulase has (76%). It also had better performance and storage stability. Compared to the covalent cross-linking Alg-SiO2 immobilized cellulase, the Sol- Gel Alg-SiO2 immobilized cellulase had better thermal stability and relative activity. For covalent cross-linking Alg-SiO2 immobilized cellulase, Michaelis–Menten constant (Km) value was 1.10 mg/ml, respectively, the same value of Sol- Gel-derived Alg-SiO2 immobilized cellulase was found to be 0.290 mg/ml.