Immobilized cellulase on Fe3O4/GO/CS nanocomposite as a magnetically recyclable catalyst for biofuel application

Abstract

Biofuel was, is, and will continue to be the most in-demand energy source in the twenty-first century. One of the most efficient and cheapest ways of producing bioethanol is through the saccharification of glucose. Lignocellulose is one of the abundant and cheap forms of cellulose that are found across the globe as the cellulose is a linear chain of glucose connected by the glycosidic bond. Agricultural biomass is the most abundant source of lignocellulose, which is wasted in millions of tons each year. The current study aims at converting the waste agricultural biomass to bioethanol by enzymatic hydrolysis followed by saccharification. Cellulase from Aspergillus niger was used in this study as a hydrolytic enzyme. To increase the stability and efficiency of the cellulase enzyme, immobilization technology was introduced in the study in which the cellulase was immobilized in the synthesized Fe3O4/GO/CS nanocomposites. The formation of Fe3O4/GO/CS nanocomposites by co-precipitation was confirmed by various instrumental data like UV–Visible spectroscopy, FTIR, XRD, VSM, and TEM. 86 % of the loaded enzyme was immobilized by simple adsorption. The optimum condition for the enzymatic hydrolysis of immobilized enzyme on cellulose substrate was found to be pH 8, temperature 80 °C, which is way higher than the optimum condition of free cellulase. Thermal stability of the immobilized enzyme was studied, which showed 99 % activity retained even after four cycles. The immobilized cellulase showed 89 % retained activity even after storing it at 4 °C for a month. The thermodynamic parameters like half-life, ΔH, ΔS, ΔG and deactivation kinetics were calculated. The inactivation energy of the immobilized enzyme was found to be 106.41KJ.mol−1. Kinetic parameter like Vmax, Km and Kcat were calculated as 26.02 ± 2.011 µmol min−1 mg−1, 2.469 ± 0.512 mM and 0.86 s−1. Wheat bran and rice bran having lignocellulose were pretreated by both acid and alkali to degrade the lignin and hemicellulose. The pretreated cellulose in the wheat and rice bran was enzymatically hydrolysed using the immobilized cellulase. The glucose obtained from the hydrolysis was fermented with Saccharomyces cerevisiae to yield 7.32 g ethanol/liter of glucose from pretreated wheat bran and 7.05 g of ethanol/liter of glucose from pretreated rice bran.