Enhanced Sulfur Dioxide Adsorption in UiO-66 Through Crystal Engineering and Chalcogen Bonding

Adsorption of corrosive SO2 gas occurs in metal-organic frameworks (MOFs) including UiO-66. Improvements in SO2 capacity is obtained through the incorporation of residual modulators in the UiO-66 framework by introducing new binding sites in the material, through residual modulators. Four residual modulators were investigated (acetic acid, trifluoroacetic acid, 3-DMAP acid, cyanoacetic acid), and the UiO-66 framework modulated with cyanoacetic acid exhibited nearly twice the SO2 uptake for the 18:1 modulator/linker synthesis ratio compared with other modulated UiO-66 structures. Density functional theory investigations confirmed that targeted host-guest interactions were maintained after the modulator was incorporated into the framework. The strongest binding energy was between SO2 and cyanoacetic acid, consistent with dynamic SO2 adsorption data, and identified contributions from both the SO2 reacting with the residual modulator and the coordinating linkers. The successful increase in dynamic SO2 capacity illustrates how often-overlooked non-covalent interactions can be used in targeted adsorption applications. Further investigation into weak electrostatic interactions for adsorption properties is also needed to advance the potential selectivity and capacity in the adsorption sphere.