Computational Exploration of a Metal(II) Catecholate-Functionalized UiO-66 Nanoporous Metal-Organic Framework for Effective NOx Capture

Metal-organic frameworks (MOFs) have attracted much attention for the effective capture of contaminants from air. Herein, density functional theory (DFT) calculations and grand canonical Monte Carlo (GCMC) simulations were combined to systematically assess the adsorption performance of the cagelike UiO-66 nanoporous MOF functionalized by metal(II) catecholate [CatM(II), where M(II) = Mg(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Pd(II), and Pt(II)] with respect to NOx potentially present at very low concentration (from the ppm to ppb levels). The adsorption modes and energetics of NOx toward metal(II) catecholate functions were first examined systematically using cluster DFT calculations in order to determine the optimum metal(II) for effective NOx capture. The best CatFe(II) was further incorporated in the crystal structure of UiO-66 and force-field parameters to accurately describe the specific interactions between Fe(II), and both NOx were derived from periodic DFT calculations and further implemented in a GCMC scheme to predict the adsorption isotherms in a whole range of gas pressure. These calculations revealed that UiO-66-CatFe(II) exhibits steep-adsorption isotherms for both NOx, leading to excellent adsorption uptake at very low gas pressure (from 10-9-10-4 bar). This finding complements the portfolio of nanoporous materials that has so far been almost exclusively tested in operation conditions at much higher NOx concentration (> 1000 ppm).