Molecular dynamics and quantum simulation of different cationic dyes removal from contaminated water using UiO-66 (Zr)-(COOH)2 metal–organic framework

Metal organic frameworks (MOFs) especially benzene-1,4-dicarboxylic acid-functionalized UiO-66 (UiO-66-(COOH)2) with distinguished properties are great candidates for dyes removal from wastewater. In the current work organ-metal with anion groups, UiO-66-(COOH)2 (MOF/(COOH)2), was selected to adsorb four toxic cationic dyes from aqueous media. The quantum chemical calculations and molecular dynamic simulation were used to evaluate the adsorption mechanism of four toxic cationic dyes (malachite green (MG), methylene blue (MB), toluidine blue (TB) and crystal violet (CV)) on the MOF/(COOH)2 in the presence of water molecules. The optimized geometry of all structures was obtained through Dmol3 module. According to the obtained results the highest adsorption energy was obtained for CV-water-MOF/(COOH)2 configuration, while the MB-water-MOF/(COOH)2 had the lowest adsorption energy. Also, the molecular electrostatic potential maps and frontier molecular orbitals (FMO) were achieved for all configurations. The HOMO and LUMO as well as energy gap (ΔEGAP) indicated that the highest adsorption affinity was belong to CV-water-MOF/(COOH)2 configuration. Accordingly, the increasing of ΔEGAP was in the following order: CV-water-MOF/(COOH)2 < MG-water-MOF/(COOH)2 < TB-water-MOF/(COOH)2 < MB-water-MOF/(COOH)2. The quantum chemical descriptors such as chemical potential, electronegativity, nucleophilicity and electrophilicity index, chemical softness and hardness were obtained from HOMO and LUMO energy levels. Consequently, the results demonstrated that the chemical reactivity, softness, and polarizability of CV dye were higher compared to other studied dyes. The results of this theoretical revealed that UiO-66-(COOH)2 as an acidic group functionalized MOF is highly recommended for removal of cationic dyes. Molecular dynamic simulations can be a very useful approach to make a brighter insight about the mechanism of cationic dyes adsorption on the MOF adsorbent and very effective from perspective of time and experimental costs.