Ion-exchange of copper into mordenite and clinoptilolite zeolites by molecular dynamics simulations and experimental investigations

Abstract

Copper-exchanged zeolites have been subjected to several investigations because of their application as selective redox-active catalysts, and sensors. However, the ability of different types of zeolites to exchange Cu ions remains a matter of debate. All-atom molecular dynamics (MD) simulations, energy dispersive X-ray spectroscopy (EDS), and X-ray Fluorescence (XRF) methods have been used to evaluate the exchange of Cu(II) in mordenite and clinoptilolite zeolites using an aqueous method in the current study. Several parameters of copper ions have been measured for both types of zeolites, such as ion exchange ratio, mean square displacement (MSD), diffusion coefficient, and radial distribution function (RDF). These parameters were calculated for each zeolite system at different Cu ion concentrations in the feed solution. Copper exchange ratio and RDF analyses revealed a higher exchange ratio of copper ions in the mordenite framework. Analysis of the potential energy indicates the major adsorption sites for mordenite and clinoptilolite, which are located in the largest cavities of the zeolites. The adsorption energy of the mordenite sites (1.52 eV) was larger than that of clinoptilolite (1.28 eV). The stronger attraction between the copper ions and mordenite sites is consistent with the lower diffusion coefficients of the ions in this zeolite. The ion-exchange abilities of the zeolites were examined using EDS analysis. According to the EDS results, the mordenite zeolite exchanged more copper ions than the clinoptilolite, which is in agreement with the computational results.