Carbon Dioxide Capture in Microporous Metal-Organic Frameworks

Metal-organic frameworks represent a new class of materials exhibiting high internal surface areas, tunable pore dimensions, and tailorable surface functionality. Research in our laboratory has focused on the development of metal-organic frameworks with surfaces bearing open metal coordination sites for high-enthalpy hydrogen adsorption. Recently, we have initiated efforts to utilize such materials for the selective capture of CO$_{2}$ from flue gas. Here, open metal coordination sites can deliver a high CO$_{2}$ loading capacity at low pressures. However, additional criteria, such as water stability and the selective binding of CO$_{2}$ over N$_{2}$, must also be taken into consideration. Towards that end, we have targeted air- and water-stable frameworks bearing surfaces coated with amine groups. For example, the use of 1,3,5-benzenetristriazolate (BTTri$^{3-})$ as a bridging ligand has led to sodalite-type frameworks such as HCu[(Cu$_{4}$Cl)$_{3}$(BTTri)$_{8}$], possessing open Cu$^{2+}$ coordination sites and exhibiting good chemical and thermal stability. Attachment of ethylenediamine to the Cu$^{2+}$ sites within this structure generates a material that selectively binds small amounts of CO$_{2}$ over N$_{2}$. Details of the characterization of this and related materials will be presented.