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Applications of porous organic cages for gas separations and storage
Krishnan, Keerthana
Krishnan, Keerthana
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2023
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Abstract
Porous Organic Cages (POCs) possess high surface area, uniform micropores and thermal and chemical stability which when combined with solid state molecular packing, not only makes them applicable in various functional applications, but also makes them stand apart from materials like metal organic frameworks, covalent organic frameworks, and zeolites. Held together by covalent bonds, POCs display a 3-dimensional pore connectivity in their crystalline form. Typically synthesized by imine bond condensation between a trialdehyde and diamine, the morphology control is directed by the diamine leading to unique packing of the cage molecule designated as CCX, and X can change from 1 denoting the name specific to the cage. Uniform pore size POCs have found themselves suitable for applications including catalysis, gas storage and gas separations.
In this work, the capability of two prototypical POCs denoted as CC3 and CC2 with limiting pore aperture of 3.6 Å to selectively separate CO2 from N2 and H2 has been demonstrated. The adsorption selectivity of CC3 for CO2/N2 and CO2/H2 were ~8 and ~20 respectively. The adsorption selectivity of CC2 for CO2/N2 and CO2/H2 were ~9 and ~35 respectively. The synthesis of continuous and defect-free CC3 membranes were validated with helium permeability as high as 4.45 × 10−7 mol/ (m2 s Pa) and He/CH4 separation selectivity as high as 8. To expand knowledge of the formation of POCs, a new POC was synthesized from CC3 and CC2 POCs by “covalent scrambling” and extensive characterization was performed on the material to perceive its structure-property relation better. Programming with R was used to comprehend the crystallinity of the material with respect to its X-ray diffraction pattern. Some preliminary work was completed (sandwich membranes and composite membranes using mesoporous MCM-41 crystals) to pave the way for the future directions of this research is also presented in this work.
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