Insights into Adsorption of NH3 on HKUST-1 Metal–Organic Framework: A Multitechnique Approach

We report a careful characterization of the interaction of NH 3 with the Cu(II) sites of the [Cu 2 C 4 O 8 ] paddle-wheel cornerstone of the HKUST-1 metallorganic framework, also known as Cu 3 (BTC) 2 . The general picture emerging from combining XRPD, EXAFS, XANES, mid- and far-IR, DRUV–vis, and EPR techniques is that the presence of traces of water has relevant consequences on the effect of ammonia on the MOF framework. NH 3 adsorption on the dry system results in a strong chemisorption on Cu(II) sites that distorts the framework, keeping the crystallinity of the material. Perturbation observed upon NH 3 adsorption is analogous to that observed for H 2 O, but noticeably enhanced. When the adsorption of ammonia occurs in humid conditions, a time-dependent, much deeper modification of the system is observed by all of the considered techniques. On a methodological ground, it is worth noticing that we used the optimization of XANES spectra to validate the bond distance obtained by EXAFS.