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

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.