Molecular Design of Solid Sorbents for Gas Capture Applications
Date
2018-04-30
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Abstract
Designing new solid sorbents can be difficult as many factors need to be considered if a better material is to be synthesized. Gas capture applications require not only a high uptake of a specific gas, but also high stability, high selectivity, and good mechanical properties. Creating coordination polymers that contain phosphonate ligands can add stability to the framework due to the strength of the metal-ligand bond., but there are many challenges with phosphonates, like the unpredictability, low crystallinity and preference for layered materials, that need to be overcome to make sorbents. The first metal-organic framework (MOF) synthesized used pyrene-1,3,6,8-tetraphosphonic acid with Cr3+, but it was synthesized using a hydrogen-bonded intermediate to overcome crystallinity issues. It had a surface area of 695 m2/g and a selectivity for CO2 over N2 of 319.5. It’s low regeneration energy and chemical stability make it interesting as a flue gas capture material. The next MOF was synthesized using Zr4+ and 1,3,5,7-tetrakis(4-phosphonophenyl)adamantane to increase stability and prevent a dense framework. The MOF had a surface area of 541 m2/g with a stability to acid. The water sorption was high at 14.5 mmol/g, making the material interesting for water adsorption processes. The last sorbents studied focused on the morphological control when using fluorene-2,7-diphosphonic acid versus the monoester, fluorene-2,7-diphosphonate bis(monoethyl ester). While studies with Co2+ showed sphere formation with the monoester, porosity and remarkable mechanical properties, the Ni2+ coordination polymer formed hollow spheres with a surface area of ~1200 m2/g. All of the materials synthesized illustrate how understanding of supramolecular concepts allow for the manipulation and improvement of properties of the desired sorbents. The thesis concludes with a discussion of the opportunities that exist in the area of solid sorbents and the future outlook of these materials.
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Keywords
Phosphonates, Metal-organic Frameworks, Gas separations, Hydrogen-bonded network
Citation
Bladek, K. J. (2018). Molecular Design of Solid Sorbents for Gas Capture Applications (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/31886