Adsorption of Sulfur Dioxide in Cu(II)-Carboxylate Framework Materials: The Role of Ligand Functionalization and Open Metal Sites.

The development of efficient sorbent materials for sulfur dioxide (SO 2 ) is of key industrial interest. However, due to the corrosive nature of SO 2 , conventional porous materials often exhibit poor reversibility and limited uptake toward SO 2 sorption. Here, we report high adsorption of SO 2 in a series of Cu(II)-carboxylate-based metal-organic framework materials. We describe the impact of ligand functionalization and open metal sites on the uptake and reversibility of SO 2 adsorption. Specifically, MFM-101 and MFM-190(F) show fully reversible SO 2 adsorption with remarkable capacities of 18.7 and 18.3 mmol g -1 , respectively, at 298 K and 1 bar; the former represents the highest reversible uptake of SO 2 under ambient conditions among all porous solids reported to date. In situ neutron powder diffraction and synchrotron infrared microspectroscopy enable the direct visualization of binding domains of adsorbed SO 2 molecules as well as host-guest binding dynamics. We have found that the combination of open Cu(II) sites and ligand functionalization, together with the size and geometry of metal-ligand cages, plays an integral role in the enhancement of SO 2 binding.