Removal of toxic heavy metal ions from waste water using superchalcogens: A theoretical study

Abstract

One of the most exciting events in chemistry is the stable assemblies of atoms, denoted by superatoms, that could mimic the behaviors of elements in the periodic table. For the first time by Jena et al., a novel type of di-anions superchalcogens (BeAl122− and TiAu122-) has been introduced based on the various electron-counting rules. Inspired by the fascinating finding of these superatoms and guided by density functional theory calculations, we propose a novel and efficient strategy to capture pollutants from waste water via adsorbing the toxic heavy metal cations (Cd2+, Hg2+, and Pb2+) by the BeAl122− and TiAu122− superchalcogens. Our results reveal that the BeAl122− and TiAu122− superchalcogens were powerful to adsorb the Pb2+, Hg2+, and Cd2+ cations in the aqueous solution. Furthermore, by investigating the hydrated cations, the adsorption of hydrated [Pb(H2O)4]2+ on the BeAl122− and TiAu122− superatoms was found thermodynamically more favorable than the [Cd(H2O)4]2+ and [Hg(H2O)4]2+. Our calculations also showed that the adsorbing heavy metal cations can considerably narrow the wide HOMO-LUMO gap and remarkably enhance the first hyperpolarizability of the pristine BeAl122− and TiAu122− superchalcogens, due to electron transfer in this type of superatoms. Moreover, the results highlight the systems with higher electron transport rates, show the larger first hyperpolarizability as well as the higher nonlinear optical response. Time-dependent density functional calculations also revealed “ligand to metal charge transfer” vertical excitations for the cation/superchalcogen systems. However, these theoretical findings might be helpful for experimental scientists toward designing high-efficient adsorbents based on superatoms for eliminating water pollutants.