Encapsulation of urea and caffeine in Cu3(BTC)2 metal-organic framework

The Cu-3(BTC)(2) metal-organic framework (MOF) (BTC = 1,3,5-benzenetricarboxylate), also known as HKUST-1 (or MOF-199), is one of the most studied MOFs because it has a large surface area, high pore volume, high chemical stability and the ability to bind water, among other molecules, by coordinating to the unsaturated Cu(II) sites. In this study, Cu-3(BTC)(2) was used for the first time to remove the pharmaceutical products of urea and caffeine. Two strategies for retention of urea and caffeine in Cu-3(BTC)(2) were studied. The first strategy corresponds to in situ encapsulation, where urea and caffeine were added to Cu-3(BTC)(2) synthesis precursors and the porous structure was formed around the urea or caffeine molecules resulting in the encapsulation. The second one corresponds to post-synthesis encapsulation. The adsorption of urea or caffeine in MOF structure was realized by adding the as-synthesized dry Cu-3(BTC)(2) into urea or caffeine aqueous solution. The results show that in situ encapsulation of caffeine and urea in Cu-3(BTC)(2) produced a guest loading of 38 and 25 wt%, respectively, whereas, post-synthesis encapsulation had a guest loading of 52 and 30 wt% for caffeine and urea, respectively.