Simultaneous Metal–Organic Framework Growth and Organic Molecule Encapsulation on Reactive Supports for Flow-Based Applications

Metal–organic frameworks (MOFs) have been extensively studied for encapsulating both small organic molecules and large biomolecules, protecting them from environmental degradation. Furthermore, MOF applications have been expanded by developing strategies for the in situ growth of MOFs on functional supports. However, there is a current lack of methods combining the in situ growth of MOFs on functional supports with the encapsulation of organic molecules. In this study, we developed a reactive ZnO-based porous polymer support that enables the simultaneous growth of the MOF ZIF-8 and encapsulation of small organic molecules using Rhodamine B (RB) and caffeine as representative examples. ZnO nanoparticles immobilized in the reactive support are converted to ZIF-8 crystals using aqueous solutions containing the target organic molecules and the organic linker 2-methylimidazole. The developed method can be implemented under both static and flow conditions due to the porous nature of the support and without compromising the encapsulation efficiency. A total uptake of 512 μg of RB was obtained in the support under static conditions, compared to 478 μg under flow conditions (0.025 mL min –1 ). The in situ growth of MOFs on reactive supports has enabled the efficient extraction of molecules via encapsulation, which would otherwise exhibit poor extraction efficiency via adsorption alone. For instance, caffeine showed only 7% adsorption on the support but achieved 93% encapsulation via ZIF-8. Additionally, this encapsulation mechanism enhanced the uptake of molecules that are efficiently surface-adsorbed on the support, such as RB. This enabled the release of the RB surface-adsorbed using acetonitrile and the release of the RB encapsulated in the ZIF-8 micropores using ethylenediaminetetraacetic acid. This strategy for encapsulating molecules of interest via the in situ growth of MOFs on functional supports holds significant potential for flow-based applications including chemical separations, drug delivery, and catalysis.