Ion-exchange materials are important for their applications for water purification and metal extraction. Metal-organic frameworks (MOFs) are attractive candidates for ion-exchange materials due to their high surface area and the variety of potential modifications to the linkers. In this project, the zirconium (IV) MOF UiO-66-NH2 was modified using a mild two-step process to form a MOF with quaternary ammonium moieties. Framework characterization using gas sorption and x-ray diffraction indicated that the modification was successful, indicated by the retained high crystallinity and decreased surface area. NMR indicated that a total of 20% of the amine groups had been transformed into quaternary ammonium ions. Anion-exchange experiments were carried out to evaluate the quaternized MOF's ability to extract tetrachloroaurate (III) (AuCl4-) from aqueous solution. However, both the modified and unmodified MOF caused a rapid decrease in the concentration of the anion as indicated by the UV-vis spectrum, which could be attributed to the amines in the MOF reducing Au3+ to Au0. The pristine UiO-66-NH2 caused a more rapid decrease in AuCl4- concentration, possibly due to the higher porosity of the unmodified framework and higher reduction activity of primary amines.

Mild two-step quaternization of amine-tethered metal-organic frameworks for anion-exchange applications

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.