Mesoporous Metal-Organic Framework with Well-Defined Cruciate Flower-Like Morphology for Enzyme Immobilization

Metal-organic frameworks (MOFs) have recently emerged as a promising candidates for the immobilization of enzymes due to their diversified structures and porosity. However, a lack of good size and morphological control over the as-prepared MOFs has limited their practical applications in some cases. Herein, instead of zeolitic imidazolate framework-8 (ZIF-8) with the standard rhombic dodecahedral morphology, we successfully synthesize a novel mesoporous catalase@ZIF composite with cruciate flower-like morphology by embedding catalase molecules into uniformly sized ZIF crystals. With extraordinarily large mesopore size and high protein loading capacity, the catalase@ZIF composites with cruciate flower-like morphology exhibit 400% higher activity than that of catalase@ZIF composites with conventional rhombic dodecahedral morphology, and show higher reusability than conventional rhombic dodecahedral morphology. More importantly, we demonstrate for the first time that the biomacromolecules (proteins) can not directly regulate the crystal size, morphology, and crystallinity of ZIF-8. Moreover, the crystal morphology of ZIF has primary dependence on concentrations of 2-methylimidazole and Zn²⁺ ions, and can be directly controlled by adjusting concentrations of Zn²⁺ ions while keeping the high concentration of 2-methylimidazole.