Polymer@MOFs capsules prepared through controlled interfacial mineralization for switching on/off enzymatic reactions

Abstract

Engineering MOFs nanocrystals into hierarchical/macroscopic structures is critical for many applications. However, defects between MOFs nanocrystals often exist due to the uncontrollable nucleation and growth in MOFs crystallization. In our study, inspired by biomineralization processes in nature, we report a facile and generic method to prepare polymer@MOFs capsules with defect-free MOFs layer through controlled interfacial mineralization. Specifically, zeolitic imidazolate framework-8 (ZIF-8) and polydopamine (PDA) capsules are used to prepare the polymer@MOFs capsules. The PDA capsules are exploited to confine Zn2+ ions within the capsule lumen and on the capsule wall. When incubated into a solution of 2-methylimidazole (2-MeIm), Zn2+ ions on the capsule wall will trigger the interfacial nucleation of ZIF-8, while Zn2+ ions in the capsule lumen will diffuse into the capsule wall and react with 2-MeIm, enabling the growth and formation of defect-free ZIF-8 nanolayer. The molecule-sieving property of polymer@MOFs capsules is tested by the controlled permeation of small molecules (methylene blue, 6.0×13.8Å2) through the capsule wall, conferring the enzyme-embedded polymer@MOFs capsules with the unique features of on/off control of enzymatic reactions over multiple reaction cycles, and high stability of entrapped enzymes against long-term storage. Through changing the species of polymer capsules, shapes of polymer capsules and species of MOFs, a series of polymer@MOFs capsules are prepared, highlighting the versatility and functionality extension of this interfacial mineralization method.