Supercritical CO2 encapsulation of bioactive molecules in carboxylate based MOFs

Caffeine and carvacrol were encapsulated using supercritical CO2 (sc-CO2) impregnation in MOFs, MIL-53(Al) and Mg-MOF-74, at different contact times. High additive loadings were achieved, 32.1 and 34.3% for caffeine, and for carvacrol 34.4 and 30.1%, respectively. The sc-CO2 encapsulation was more effective compared to the typical liquid phase encapsulation in ethanol. In fact, the encapsulation in Mg-MOF-74 was only possible in sc-CO2, null loading was observed in the liquid ethanol phase process. The products required no purification and the excess of additives could be reused. In all the studied cases, the materials maintained their crystalline structure and MIL-53(Al) displayed its characteristic flexibility adapting its structure to the additives. The total release of caffeine and carvacrol from Mg-MOF-74 was produced after 5 h in distilled water, while in the case of MIL-53(Al) no release was observed for 10 days.