Molecular simulation of adsorption properties of thiol-functionalized titanium dioxide (TiO2) nanostructure for heavy metal ions removal from aqueous solution

We investigated the adsorption of Cd ion as a primary contaminant heavy metal in drinking water on titanium dioxide (TiO2) and thiol-functionalized TiO2 (thiol-TiO2). The dispersion corrected density functional theory (DFT-D2) calculation is used for structural relaxation and second-order MP2 (second-order Moller-Plesset) calculations for interaction energy (E-int) estimation. The results reveal that the Cd bound very strongly (E-int: -4.566 eV) to the TiO2 and strongly to the thiol-TiO2 (E-int: -1.882 eV). Our findings show that the H2O molecule is adsorbed very strongly on the TiO2 surface (E-int -4.535 eV) while it is attached weakly to the thiol-TiO2 (E-int -0.076 eV). The DFT-based molecular dynamic (MD) simulations at ambient conditions reveal that water molecules are first adsorbed on the nano-TiO2 surface, and then the Cd ion is co-adsorbed on the surface. Meanwhile, for thiol-nanoTiO(2), a new chemical bond was formed between the Cd ion and S atom of the thiol group at 1 ps. The analysis of the AIM (Atom-In-Molecule) theory demonstrated that the types of interactions are typical for the electrostatics accompanied with partial covalent bonding between Cd ion and both O and S atoms. Our molecular simulations offer a well-founded understanding of the adsorption mechanisms of heavy metals on TiO2 and thiol-TiO2 at ambient conditions. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the adsorption of Cd ion on titanium dioxide (TiO2) and thiol-functionalized TiO2 (thiol-TiO2). The results showed strong binding of Cd to both TiO2 and thiol-TiO2, with stronger adsorption of water molecules on TiO2 compared to thiol-TiO2. Molecular simulations revealed that Cd ion adsorption occurred after water molecule adsorption on nano-TiO2, while a new chemical bond was formed between Cd ion and thiol group in thiol-nanoTiO2. The analysis demonstrated electrostatic interactions and partial covalent bonding between Cd ion, O atom, and S atom.