▎ 摘　　要

Cellulases from Aspergillus niger (E) and Cellic CTec2 (E2) were immobilized onto graphene oxide coated with magnetic nanoparticles of Fe3O4 and NiFe2O4. Immobilization was performed using various concentrations of cellulase (2, 5 and 10 mg/ml) at different incubation times (2, 4, 6 and 8 h) to obtain maximum immobilization efficiency. The enzymatic activity of immobilized cellulase was investigated at different pH (4, 5, 6, 7 and 8) and temperatures (40, 50, 60, 70 and 80 degrees C) which pH 5 and 50 degrees C were determined as optimum values. Thermal stability of immobilized cellulase at 50 and 60 degrees C showed that it is more stable than free cellulase; at least 65% of its activity was maintained at 60 degrees C for 3 h. The kinetic parameters of immobilized cellulase were determined using various concentrations (0.5, 1, 2 and 2.5% w/v) of carboxymethyl cellulose. Hydrolysis of raw and pretreated rice straw was performed using immobilized E and E2 for 72 h at 50 degrees C. Fermentable sugars from hydrolysis of rice straw using immobilized E onto Fe3O4-GO and NiFe2O4-GO and immobilized E2 onto NiFe2O4-GO were equal to 1.92, 1.88 and 7.2 mg/ml (first use) and 1.1, 1.0 and 2.8 mg/ml (second use), respectively. After two cycles of hydrolysis, immobilized cellulase on NiFe2O4-GO showed better reusability and produced more fermentable sugars compared to cellulase immobilized on Fe3O4-GO. The main aim of this work was to compare immobilization performance of these 2 cellulase species on the mentioned supports.