Development of an Immobilized Cellulase System Based on Metal–Organic Frameworks for Improving Ionic Liquid Tolerance and <i>In Situ</i> Saccharification of Bagasse

Abstract

To achieve high ionic liquid (IL) tolerance and promote in situ enzymatic hydrolysis of biomass, four metal–organic framework (MOF) carriers, including ZIF-8, UIO-66-NH2, MIL-100-Fe, and PCN-250, were used for cellulase immobilization through simple physical adsorption. The results showed that ZIF-8 had the largest enzyme adsorption capacity at 176.16 mg/g support. In addition, the immobilized cellulases activity was evaluated in the presence of 1-ethyl-3-methylimidazolium diethylphosphate ([Emim]DEP) by using caryboxymethyl cellulose (CMC) and filter paper (FP) as substrates. When IL concentration increased from 0% to 50% (v/v), the immobilized cellulase displayed superior IL tolerance compared with free cellulase. In particular, ZIF-8-immobilized cellulase exhibited a remarkable IL tolerance, in which the activity of caryboxymethyl cellulase (CMCase) and filter paper cellulase (FPase) were increased by 112.59% and 59.86% in 50% (v/v) [Emim]DEP, respectively. The analysis of kinetic parameters further suggested that the immobilized cellulase had a lower equilibrium dissociation constant (kd) value and a higher final enzyme plateau activity (ap) value in a reaction system involving IL, indicating that the immobilized enzyme can effectively reduce cellulase inactivation caused by IL. Eventually, ZIF-8-immobilized cellulase with in situ hydrolysis of bagasse increased by 92.92% compared with free cellulase in 50% (v/v) [Emim]DEP.