Mof-derived hollow-open hierarchically porous carbon spheres for enzyme encapsulation and biocatalysis

Abstract

The preparation of hollow hierarchically porous Zeolitic Imidazolate Framework-8 (ZIF-8), followed by its derivation into carbon materials, emerges as an effective approach to overcome the issues of limited pore size and poor stability encountered by traditional ZIF-8 in enzyme immobilization applications. In this study, a simple and distinctive pathway was employed to fabricate spherical ZIF-8 with a hollow-open hierarchically porous structure (KHZIF-8), which was carbonized into a promising immobilized enzyme carrier, hollow-open hierarchically porous carbon spheres (C/KHZIF-8-X, where X signifies the carbonization temperature). A suite of analytical techniques was utilized to elucidate the transformation of ZIF-8 into derived carbon. Compared to ZIF-8, C/KHZIF-8-X demonstrates enhanced chemical stability in aqueous systems for enzyme immobilization. C/KHZIF-8–800, produced through optimized carbonization, achieved Candida rugosa lipase (CRL) loading of 177.4 mg g⁻¹ and relative activity of 81.4 %, while C/ZIF-8@CRL exhibited lower enzyme loading (66.3 mg g⁻¹), and the relative activity based on unit enzyme amount decreased to 66.6 %. Furthermore, the successful encapsulation of catalase confirmed the potential of C/KHZIF-8–800 as a universal platform for biomolecule immobilization. In application, C/KHZIF-8–800@CRL catalyzed the synthesis of oleic acid sterol esters, achieving a maximum conversion rate of 80.9 %. This study shed new light on optimizing the structure and properties of ZIF-8 and developing MOF-based immobilized enzyme reactors.