Defect and Linker Effects on the Binding of Organophosphorous Compounds in UiO-66 and Rare-Earth MOFs

The adsorption of chemical warfare agents and their simulants by Zr (UiO-66) and rare-earth (Y, UiO-66DOBDC analog) -based metal organic frameworks (MOFs) is explored here using density functional theory. In particular, we investigate the role of linker functional group (OH, H) and metal atom identity on the binding energies of organo- phosphorous compounds. Commonly used cluster approximations for MOF secondary building units and various optimization constraints are compared with three-dimensional periodic results. An in-depth scan of potential binding sites and orientations reveals little effect due to metal identity, whereas the effect of linker functionalization depends on the substrate. This finding strongly suggests that full linkers and functional groups should be included in cluster models. Importantly, defect sites show considerably improved binding of organophosphorous compounds as compared to ideal clusters. Favorable binding is also demonstrated at two additional adsorption sites, ZrOH and mu 3-OH, that likely play a role in the initial adsorption process. The results presented here portray the importance of including full threedimensional pore structures in the adsorption process of organophosphorous compounds in MOFs; a critical first step in the degradation of these harmful chemicals.