Riascos Rodríguez, Karina

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    Porous coordination pillared layer networks: Hysteretic gas adsorption and functionalization for superior CO2 uptake
    (2020-02-03) Riascos Rodríguez, Karina; Hernández Maldonado, Arturo J.; College of Engineering; Briano, Julio G.; Martínez Iñesta, María M.; Suleiman Rosado, David; Department of Chemical Engineering; Lorenzo, Edgardo
    Porous coordination polymers (PCPs) are crystals holding pore sizes and shapes with tremendous capabilities for carbon capture based on adsorption. Coordination pillared layer networks, with copper as central node, Cu2+-CPL-n, are PCPs with considerable potential for CO2 adsorption, showing stability, good performance for gas storage and delivery, and an intriguing hysteretic adsorption found related to the maximum gas loading. In this work, the hysteretic behavior of a selected set of CPL-n materials upon CO2 loading was addressed through adsorption and concomitant structural variation studies. These observations showed foundations to associate structural long-range distortions, and flexible-responsiveness, to interactions induced by the adsorbate. In situ CO2 adsorption and powder X-ray diffraction (XRD) measurements at room temperature, onto Cu2(pzdc)2(bpy), up to 7 bar, indicated changes in the unit cell volume. The onset of the adsorption hysteresis corresponded to a full occupancy of the pore volume, at CO2 partial pressures above 2 bar. Further assays were performed to functionalize CPL-n materials and to improve the adsorbate-adsorbent interactions, decorating prone functional groups of ligands by an alkaline metal. Cu(pzdc)(pia), which contains amide functional groups, was used to test a post-synthesis lithiation rationale. Synchrotron powder X-ray diffraction (XRD) results allowed structural elucidations to corroborate micro porosity after functionalization. CO2 adsorption up to 7 bar at room temperature showed a concave up isotherm shape with significant hysteresis upon desorption, which suggests structural variations consequent to different or stronger adsorption sites along the pores. Results from elemental, thermal gravimetric and crystal refinement analyses indicated that the lithium content is ca. 3 Li per asymmetric unit. Raman scattering shifts suggested Li positions near the amide and nitrogen pyridyl groups of pia ligand. In situ XRD and CO2 adsorption tests performed at pressures up to 50 bar and ambient temperature substantiated the structural changes anticipated by hysteresis.