Copper insertion in UiO-66 analogues for ammonia removal applications
Joshi, Jayraj N.
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Development of novel materials for ammonia capture in air filtration devices is of particular importance due to the high availability and toxicity of the gas, but materials currently employed for air purification offer insufficient protection. Characteristics of porosity, stability, and tunability in metal organic frameworks, however, makes this class of nanoporous, crystalline material suitable for enhancing ammonia uptake performance of air purification equipment. Post synthetic modification of UiO-66 type MOFs with copper resulted in the creation of UiO-66-(COOCu)2, whose copper carboxylate functional groups are highly favorable for ammonia chemisorption. Experiments showed UiO-66-(COOCu)2 to possess a high uptake capacity for ammonia, while showing negligible loss in surface area and crystallinity following humid and dry ammonia exposure, and water vapor adsorption experiments. However, the –COOCu moieties were thought to cause significant pore blocking, likely hindering access of ammonia guest molecules into the pore space. Recent studies have shown carboxylic acid functionalities can be incorporated into UiO-66 through missing linker sites, resulting in higher surface area and pore accessibility, while incorporating carboxylic acid functionalities that can be used for copper coordination to enhance ammonia uptake. This study focuses on the functionalization of defective UiO-66 with copper carboxylate groups, where copper loading and ammonia uptake performance was studied for comparison to other materials used for ammonia adsorption. Furthermore, the kinetic effects of copper loadings on linker and defect site functionalized carboxylic acid groups on UiO-66 were studied, along with their effect on dynamic ammonia capacity.