Microwave synthesis of UiO-66 with encapsulated caffeine: Liquor mother reuse and release from polyamide composites

Abstract

In this study, UiO-66 was in-situ synthesized with encapsulated caffeine (CAF@UiO-66) following a one-pot DMF-free microwave-assisted method. The microwave-assisted approach allowed for an efficient and fast encapsulation of caffeine within the metal-organic framework in a single step thus achieving a more environ- mentally friendly process. It was shown that the CAF@UiO-66 solid was capable of gradually dosing caffeine into aqueous media over a long period. Moreover, the recovered synthesis solution containing residual caffeine and solvent was successfully reused in several encapsulation cycles, giving capsules that showed good caffeine release properties. In addition, CAF@UiO-66 solids were incorporated into polyamide 6 (PA6) fibers through an extrusion process without altering their physicochemical properties. These composites showed a gradual and sustained release of caffeine, extending the dosage time and shelf life of the additive which made it potentially useful for its application in functional textile products. Finally, the release of caffeine from the capsules was fitted to a Fickian model while that from the polymeric composites was adjusted to the semi-empirical Korsmeyer- Peppas model.