Bionic mineralization growth of UIO-66 with bovine serum for facile synthesis of Zr-MOF with adjustable mesopores and its application in enzyme immobilization

A metal-organic frameworks (MOFs) with adjustable mesopores was prepared through bionic mineralization using protein as template in this paper. By regulating the content of bovine serum, pore structures of different sizes (6.46, 7.55, 10.80 nm) were obtained, used for the immobilization of enzymes (HRP, laccase and cellulase). It was found that the UIO-66 with a pore size of 6.46 nm exhibited the highest loading capacities for the investigated three enzymes. Under optimized conditions for immobilization, the maximum loading capacity of HRP, laccase and cellulase was 205.7, 214.2 and 203.9 mg g-1, respectively. It should be noted that the stabilities of the three immobilized HRP@UIO-66, laccase@UIO-66 and cellulase@UIO-66 were significantly improved due to the favorable fitting between the pore size of the carrier material and the enzyme molecular size. In particular, the substrate affinity of the immobilized HRP@UIO-66 (0.120 g L-1) is similar to that of free HRP (0.122 g L-1). It is mainly due to that the appropriate porous structure of the carrier could avoid the obstruction of the substrate mass transfer channel after the adsorption of enzyme molecules. Moreover, the porous structure has a certain enrichment effect on the substrate, which promotes the catalytic efficiency of immobilized enzymes.