High yield immobilization of cellulase on the polypyrrole Fe ₂ O ₄ SiO ₂ nanocomposite: its stabilization and applicability in the hydrolysis of microcrystalline cellulose in a batch process

The current work investigated the use of a specific nanoconjugate, polypyrrole coated magnetic silicon dioxide nanocomposite (Fe₂O₄SiO₂/PPyNC), for effective immobilization <i>Aspergillus niger</i> cellulase, onto Fe₂O₄SiO₂/PPyNC to produce NC-bound cellulase (NBC). The cellulase enzyme was chemically attached to the NC material using glutaraldehyde crosslinking and effective binding of the cellulase was verified using transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray analysis, X-ray diffraction, Brunauer-Emmett-Teller surface analysis and scanning electron microscopy. The nanobiocatalytic NBC preparation exhibited significantly enhanced activity in comparison with its soluble counterpart. The immobilization of cellulase resulted in significant improvements in pH, temperature, and storage stability profiles. The cellulase covalently coupled to Fe₂O₄SiO₂/PPyNC exhibited a lower K_M value, suggesting a 1.49-fold increase in affinity of the NBC toward the substrate compared to the soluble enzyme. The covalently immobilized cellulase retained 85.3% of its original activity even after undergoing 8 consecutive applications. The NBC formulation exhibits improved biocatalytic activity, stability, and reusability characteristics. These qualities were successfully utilized for facilitating the hydrolysis of microcrystalline cellulose (MCC) and complex lignocellulosic biomass including wheat straw, and sugarcane bagasse, resulting in the production of significantly higher sugar yields when compared to the hydrolysis by soluble cellulase.