Cellulase immobilization within zeolitic imidazolate frameworks by in situ encapsulation

Abstract

The industrial applications of cellulase are often restricted by its high cost and poor stability under extreme conditions. In this study, cellulase was immobilized using zeolitic imidazolate framework-8 (ZIF-8) through a one-pot encapsulation method, resulting in the formation of cellulase@ZIF-8 composite designed to address these challenges. The effects of varying Zn²⁺/2-methylimidazole molar ratios and different amounts of cellulase on the properties of cellulase@ZIF-8 were systematically investigated. Cellulase was found to act as a nucleation site, accelerating the formation of cellulase@ZIF-8 while promoting controlled crystal growth. At lower Zn²⁺/2-methylimidazole ratios, cross-shaped cellulase@ZIF-8 crystals with moderate enzymatic performance were obtained. Conversely, at higher Zn²⁺/2-methylimidazole ratios, the resulting spindle-shaped cellulase@ZIF-8 crystals exhibited superior enzyme activity of 327.8 U/g, and a relative activity of 88.6 %. Furthermore, this composite demonstrates excellent thermal and storage stability. The immobilized enzyme retained 92.8 % of its activity at a temperature of 70 °C. Additionally, it maintained 69.8 % of its relative enzymatic activity after undergoing five cycles. These findings have significant implications for the future application of cellulase@ZIF-8 composites in efficient and cost-effective lignocellulosic bioconversion.