The template role of caffeine in its one-step encapsulation in MOF NH-MIL-88B(Fe).

A simple and efficient one-step encapsulation of caffeine was carried out in MOF NH-MIL-88B(Fe) and compared to the traditional three-stage synthesis-activation-encapsulation procedure. Caffeine was added to the synthesis solution of a MOF whose structure was formed around the caffeine itself. The caffeine loading was 35 wt%.

CAF@ZIF-8: one-step encapsulation of caffeine in MOF.

Two strategies for encapsulating caffeine in ZIF-8 were carried out in this work: (1) one-step, in situ encapsulation where caffeine is added to a ZIF-8 synthesis solution and the MOF structure is formed around the entrapped molecule; and (2) ex situ encapsulation whereby caffeine is put into contact with previously synthesized or purchased ZIF-8. The products obtained were analyzed with XRD, TGA, Vis-UV, GC-MS, FTIR, (13)C NMR, and N 1s XPS to compare both encapsulation methods. Chemical and structural evidence indicated that the preferential adsorption site of caffeine molecules inside the ZIF-8 structure is near the methyl and CH groups of 2-methylimidazole ligand.