Meza-Morales, Paul de J.

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    Computational study of the physical adsorption of CO₂ on novel sorbents based on porous coordination polymers
    (2017) Meza-Morales, Paul de J.; Curet-Arana, María C.; College of Engineering; Santana-Vargas, Alberto; Marcelo-Suárez, Oscar; Hernández-Maldonado, Arturo J.; Department of Chemical Engineering; Parés-Matos, Elsie I.
    CO2 capture has motivated the design and synthesis of a large number of adsorbent materials. An example of these materials are the coordination pillared-layers (CPLs), which have emerged as possible candidates for CO2 adsorption related applications. CPLs consist of 2D layers formed by Cu2+ and the ionic pyrazine-2,3-dicarboxylate (pzdc2-), and are separated by organic pillar-ligands. The main objective of this dissertation is to understand the CO2 adsorption on CPLs. Computational methods, such as density functional theory (DFT) calculations and grand canonical Monte Carlo (GCMC) simulations were used to get molecular-level insights about CO2 interactions and the structural changes that CPLs frameworks may undergo upon CO2 adsorption. Our DFT results indicated that the pore-exposed carboxylate groups in the CPL frameworks exhibited a strong charge separation, a mixed electrostatic potential, and a high electric field gradient. The principal interacting sites are the pore-exposed carboxylate groups, the aromatic ring from pyrazine-2,3-dicarboxylate groups, and some chemical functionalities at the pillar-ligands. The CO2 electrostatic potential upon interaction revealed that the interaction is dictated by the coupling of the electrostatic potential between the CO2 and the CPL cluster model. The possible structural changes upon CO2 adsorption were analyzed by computer-constructed frameworks or periodic DFT calculation. By comparing the simulated CO2 isotherm obtained for each one of the frameworks with the experimental CO2 isotherms, we reproduced and traced back the structural changes upon CO2 adsorption. Our results demonstrated that CPL-bpp undergoes a unit cell contraction at a low CO2 loading. CPL-n (n=2, 4, and 5), however, exhibits fewer structural changes at low CO2 loading. To trace back the CO2 adsorption isotherms at high pressures, structural changes were considered including those which enabled higher pore volumes, such as ligand rotation or unit cell expansion. Desorption measurements suggest that hysteresis in the CO2 isotherm may also be linked to these structural changes, and measured adsorption/desorption cycles showed that these structural changes are reversible.