The interaction and mechanism between threonine-montmorillonite composite and Pb2+ or Cu2+: Experimental study and theory calculation

The maximum adsorption capacities of threonine-montmorillonite (Thr-Mt) composite to Pb2+ and Cu2+ in aqueous solution were higher than that of original sodium-montmorillonite (Na-Mt). Molecular dynamics (MD) simulation and Multiwfn wavefunction program based on density functional theory (DFT) were exploited to probe the interaction and mechanism between threonine-montmorillonite composite and Pb2+ or Cu2+. Moreover, for the first time, Independent Gradient Model (IGM) analysis was utilized to decode the interaction essence among Thr, Mt. and Pb2+ or Cu2+ to reveal the removal mechanismof Thr-Mt to Pb2+ and Cu2+. MD-results indicated that the arrangement of Thr(+) presented a preferred almost vertical orientation, which was consistent with the X-ray diffraction (XRD) result. There was hydrogen bonding between carboxyl group or hydroxy group of Thr(+) and Mt. surface. Multiwfn calculation implied that the minimum points of ESP and ALIE were located near the O atoms of hydroxyl group and carboxyl group, which were most likely providing the lone pair electron to form a complex with themetal ion,which was accordance with the result of basin analysis. IGManalysis vividly revealed that O atoms of carboxyl group and hydroxyl group were binding sites, and the interaction between Pb2+ and Na-Mt or Pb2+ and Thr-Mt was stronger than that of Cu2+, which was well consistent with the experimental conclusion. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study showed that the adsorption capacity of threonine-montmorillonite composite for Pb2+ and Cu2+ was higher than original sodium-montmorillonite. Molecular dynamics simulation and wavefunction program based on density functional theory were used to investigate the interaction mechanism, and Independent Gradient Model analysis was applied to decode the removal mechanism of Thr-Mt to Pb2+ and Cu2+.