Avaliação da estrutura e adsorção de espécies sulfuradas no sistema CuCl2@UiO-66(Zr)

Abstract

First principles calculations on periodic boundary conditions based on Density Functional Theory (DFT) were performed to investigate the adsorption of water, ethanol, carbon dioxide and sulfur compounds (H2S, COS, EtSH, Met-S -Et, DMDS, Et-S-S-Et) in the CuCl2@UiO-66(Zr) system. Firstly, the preferential position of a copper chloride fragment in the structure of the UiO-66(Zr) MOF was evaluated, where the model selected for the structure doped with the fragment showed good agreement with experimental parameters of the MOF. Electronic structure calculations (charge density difference, Bader charges, pDOS, band structure) were performed in order to evaluate the material properties and assist in choosing sites for the adsorption of molecules in the structure cavities. For the calculations, the GGA-PBE functional and the Grimme DFT-D3 correction were used. This last variable is an essential tool for describing dispersion interactions, as is the case of molecules adsorbed on porous materials. The copper atom has strongly correlated d electrons, and therefore, a methodological study of incorporating the Hubbard correction was also implemented. The investigation of structural and electronic properties showed that the use of the correction did not significantly alter the results of the calculations, and as a result, the Hubbard correction was not used in the study of adsorbate-adsorbent interactions. The adsorption energies of the molecules in the UiO-66(Zr) MOF and in the CuCl2@UiO-66(Zr) system were calculated considering the molecules in the gaseous state. It was possible to determine the order of selectivity for the two materials based on the calculated adsorption energies, where a considerable improvement in the adsorption energies of all molecules studied was observed with the presence of the copper chloride fragment in the MOF. The results indicate that both UiO-66(Zr) and the CuCl2@UiO66(Zr) system can be used as potential selective adsorbents for the sulfur compounds DMDS, Et-S-S-Et, and Met-S-Et in the presence of CO2 and water vapor, with the structure doped with the copper chloride fragment showing more favorable adsorption energies.