(678c) Engineering Copper Carboxylate Functionalities on Water Stable Metal-Organic Frameworks for Enhancement of Ammonia Removal Capacities

Functionalization of copper carboxylate groups on a series of UiO-66 metal-organic framework (MOF) analogues and their corresponding impact on humid and dry ammonia adsorption behavior were studied. Relative locations of possible carboxylic acid binding sites for copper on the MOF analogues were varied on ligand and missing linker defect sites. Materials after copper incorporation exhibited increased water vapor and ammonia affinity during isothermal adsorption and breakthrough experiments, respectively. The introduction of copper markedly increased ammonia adsorption capacities for all adsorbents possessing carboxyl binding sites. In particular, the new MOF UiO-66-(COOCu)₂ displayed the highest ammonia breakthrough capacities of 6.38 and 6.84 mmol g^–1 under dry and humid conditions, respectively, while retaining crystallinity and porosity. Relative carboxylic acid site locations were also found to impact sorbent stability, as missing linker defect functionalized materials degraded under humid conditions after copper incorporation. Post-synthetic metal insertion affords a method for adding adsorption moieties that are analogous to open metal sites while maintaining good structural stability. Since open metal site MOFs often degrade following adsorbate interactions with their metal centers, this generic strategy can be applied to other applications to engineer chemisorption sites within a framework while preserving the chemical stability of the adsorbent.