Arrieta Pérez, Rodinson R.

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    Synthesis and characterization of flexible pillared-layer structured porous coordination polymers and determination of gas adsorption-desorption properties
    (2018-05) Arrieta Pérez, Rodinson R.; Hernández Maldonado, Arturo J.; College of Engineering; Curet Arana, María C.; Mendez Roman, Rafael; Suleiman Rosado, David; Acevedo Rullan, Aldo; Department of Chemical Engineering; Hernández Rivera, Samuel P.
    Porous coordination pillared-layer structured polymers are a particular category of 3D uniform crystal materials constituted by well-defined two-dimensional layers (specially formed by a combination of metal ion or metal cluster and anionic organic ligands) interconnected by organic molecules used as pillars. A thorough research study has been dedicated to a subset of porous coordination polymers with Cu2(pzdc)(L) frameworks, which are prepared using copper (Cu2+) and pyrazine-2,3-dixarboxylate (pzdc) as layers and a series of N-donor bi-pyridyl ligands (L) as pillars. An important characteristic associated to this type of material is its designability, namely, a variety of isostructural crystals could be synthesized with a diversity of pore sizes and surface chemical content upon substitution of the pillar ligand. Therefore, this work focuses on the development of two new pillared-layer porous materials using (1) 1,3-bis(4-pyridyl)propane (bpp) and (2) 1,3-bis(imidazol-1-yl)benzene (bix) as organic pillars (L) in an attempt to improve properties related to structural flexibility and thermal stability; and to provide a porous surface that interacts significantly with CO2, either for its storage/delivery or for its separation from light gas mixtures. These two porous coordination polymers were successfully synthesized, and their crystal structures refined using a combination of high resolution X-ray diffraction (XRD) patterns and Rietveld refinement techniques. Both materials crystallized in a monoclinic P21/c space group in which the copper atom coordinates to three pzdc units and a half of the pillar unit with a distorted square-pyramidal geometry. Thermal studies based on thermal gravimetric analysis (TGA) and in situ XRD/differential scanning calorimetry (DSC) showed that the material containing bix has a significantly improved thermal stability, by an average margin of 55 K when compared with other isostructural materials. This is due to the presence of imidazole groups in the pillar in comparison to traditional di-pyridyl-based ligand. Furthermore, determination of N2 and CO2 adsorption isotherms at cryogenic conditions for both materials presented a phenomenon associated to framework expansion in concomitant with the uptake of CO2. This was also confirmed at 298 K and gas pressures up to 50 atm. Meticulous experiments at ambient temperature and CO2 pressure up to 7 atm varying the equilibration time interval evidenced that the aforementioned structural expansion had a larger time scale than the adsorption kinetic. On the other hand, although the pillared-layer built with bpp showed a stronger interaction with CO2, the presence of di-imidazole fractions in bix resulted in an interesting pore surface with higher affinity toward CO2.