Cellulase immobilization on zeolitic imidazolate frameworks for boosting cellulose hydrolysis at high solids loading

This study investigates the cellulase immobilization onto zeolitic imidazolate frameworks (ZIFs) to enable efficient cellulose hydrolysis at high solids loading. Different ZIF carriers (ZIF-8, ZIF-8-NH2, Fe3O4@ZIF-8, and Fe3O4@ZIF-8-NH2) were prepared and characterized. The resulting ZIF-immobilized cellulases were subsequently analyzed for their loading capacity and enzyme activity, as well as their biochemical properties such as temperature stability, pH stability, storage stability, enzyme leaching, and enzyme kinetics. Results revealed that the cellulase immobilized on Fe3O4@ZIF-8-NH2 exhibited an exceptional loading capacity of 359.89 mg/g and a relative enzyme activity of 69.39%. Remarkably, at a solid loading of 15% (w/w) and an enzyme dosage of 5 FPU/g cellulose, the Fe3O4@ZIF-8-NH2 immobilized cellulase demonstrated a 20.44% higher hydrolysis yield compared to the free cellulase. Furthermore, this immobilized enzyme system displayed robust reusability, retaining 71.03% of its initial activity even after 10 cycles of reuse. A proposed mechanism of enhanced enzymatic hydrolysis by ZIF-immobilized cellulases was also presented. These findings have significant implications for the future application of ZIF-immobilized cellulases in efficient and cost-effective lignocellulosic bioconversion.