Abstract
In this work, porous biochar was obtained from sugarcane bagasse by alkali activation and pyrolysis and then magnetized with γ-Fe2O3 by calcination. After functionalization with chitosan and activation with glutaraldehyde, the as-prepared chitosan/magnetic porous biochar served as a support to immobilize cellulase by covalent bonds. The immobilization amount of cellulase was 80.5 mg cellulase/g support at pH 5 and 25 °C for 12 h of immobilization. To determine the enzymatic properties, 1% carboxymethyl cellulose sodium (CMC) (dissolved in 0.1 M buffer) was considered as a substrate for hydrolysis at different pH values (3–7) and temperatures (30–70 °C) for 30 min. The results showed that the optimum pH and temperature of the free and immobilized cellulase did not change, which were pH 4 and 60 °C, respectively. The immobilized cellulase had a relatively high activity recovery of 73.0%. However, it also exhibited a higher Michaelis–Menten constant (Km) value and a slower maximum reaction velocity (Vmax) value compared to the free enzyme. In the reusability assay, the immobilized cellulase showed initial glucose productivity of 330.9 mg glucose/g CMC and remained at 86.0% after 10 uses. In conclusion, the chitosan/magnetic porous biochar has great potential applications as a support for enzyme immobilization.
Highlights
In recent years, using biomass for bioethanol production has garnered great interest
Cellulose and hemicellulose can be hydrolyzed to reducing sugars, and the sugars can be fermented into ethanol
Based on the patterns of the biochar/γ-Fe2 O3, all of the diffraction peaks can be indexed to γ-Fe2 O3 according to JCPDS no. 39-1346 [43], which indicates that γ-Fe2 O3 grew on the surface of the porous biochar
Summary
In recent years, using biomass for bioethanol production has garnered great interest. Cellulose and hemicellulose can be hydrolyzed to reducing sugars, and the sugars can be fermented into ethanol. For the process of hydrolyzing lignocellulosic materials, the use of strong acids or alkalis increases the burden on the environment and equipment, but enzymatic hydrolysis would not. Enzymatic hydrolysis of lignocellulosic should be a greenway to produce fermentable reducing sugars [1,2,3]. A composite enzyme, is mainly composed of endo-l, 4-β-d-glucanase, exo-l, 4-β-d-glucanase, and β-glucosidase. Endoglucanases randomly hydrolyze the glycosidic bonds in the amorphous regions of cellulose to produce oligomers with several degrees of polymerization. Exoglucanase hydrolyzes the β-1,4-glycosidic bond of the oligomer to produce cellobiose. Some factors limit the application of free cellulases, such as changes in pH, temperature, and ionic strength, product inhibition, and difficulty in recovering from the reaction medium. It is meaningful to improve the stability and reusability of cellulase [5,6]
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