Theoretical study of M2CO2 MXenes stability and adsorption properties for heavy metals ions removal from water

Heavy-metals ions are one of the reasons to cause the pollution of water. The toxic heavy metal ions, such as Pb2+ and Cu2+, have been aroused worldwide concern due to their high toxicity and carcinogenicity. Two-dimensional (2D) transition metal carbide materials (MXenes) exhibit the hydrophilic surface, and the excellent chemistry stabilities, and can be the potential materials for water decontamination field. Here, by using density functional theory calculations, the adsorption be-haviors of heavy metals, Ag, Au, Cu, Pb, and Zn on M2CO2 (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Ta, and W) are investigated. Results show that Pb can stably be adsorbed on V2CO2, Cr2CO2, and Zr2CO2 MXenes with the corresponding adsorption energy lower than 0 eV. Densities of states and charge transfers analysis show that the hybridization of O* p orbital with Pb p and d orbitals promote the binding strength of M2CO2 (M = V, Cr, Zr) with Pb. In addition, it shows that the high Pb coverage on M2CO2, the F mixed in the terminal O* of M2CO2, and the strain in M2CO2 can alter the adsorption ability of M2CO2 for Pb. Ab initio molecular dynamics (AIMD) simulations results indicate that the adsorbed Pb on the M2CO2 cannot aggregate into clusters at conducting temperature (300 K). Moreover, the results of the reaction energy, the binding energy, and the formation energy of hydrated Pb2+ ([Pb(H2O)n]2+) on M2CO2, and the change of bond lengths of Pb-O, dPb-O in ([Pb(H2O)n]2+) indicate that the Pb2+ can be efficiently removed from waste water even it was hydrated into [Pb(H2O)n]2+. This work illustrates that the 2D MXenes can be the promising materials for the removal of toxic metals (such as Pb2+) from water.