Macro porous ZIF-8 beads: Promising supports for enzyme immobilization

In recent years, metal–organic frameworks (MOFs) have emerged as promising supports for enzyme immobilization because they are highly designable and structurally diverse. However, the high porosities of conventional MOFs cannot be fully utilized for reactions involving large molecules, such as triglyceride transesterification reactions that produce biodiesel. Macroporous MOFs have been used to enhance diffusivity and, consequently, the reaction rate. Modifying MOFs with alginate to form MOF–polymer beads has also been proposed as a method for simplifying separation and reusability. Macroporous ZIF-8 (M-ZIF-8), sodium alginate ZIF-8 beads (SA@ZIF-8), and M-ZIF-8 combined with SA@ZIF-8 (SA@M-ZIF-8) were prepared for immobilizing lipase. M-ZIF-8 showed the highest adsorption capacity of 113.7 mg/g at 40 °C and was found to be more thermodynamically stable than ZIF-8. The experimental data for all three supports are best fitted to the Freundlich isotherm model. The adsorption kinetic data for M-ZIF-8 and SA@M-ZIF-8 are best described by a pseudo-first-order model, whereas a pseudo-second-order model provided a better fit for SA@M-ZIF-8. Lipase immobilized on M-ZIF-8 showed the highest catalytic activity, whereas that immobilized on SA@M-ZIF-8 showed the best reusability.