Mechanism study of Cd(II) ion adsorption onto resins with sulfonic/phosphonic groups using electronic structure methods

Abstract

Cadmium is a persistent bio-accumulative toxic metallic element causing hazardous impacts on environment. Through adsorption tests, it was found that Dowex G-26 resin with sulfonic group and Puromet™ MTS9570 resin with both sulfonic and phosphonic groups had excellent performance for Cd (II) ion removal from aqueous solution. To understand the adsorption mechanism of Cd(II) ion onto Dowex G-26 and Puromet™ MTS9570 resins, a density functional theory (DFT) B3LYP (Becke, 3-parameter, Lee–Yang–Parr) method and an ab initio Hartree-Fock (HF) method were employed to calculate the electronic structure properties including Mulliken population analysis, Mulliken charges of atoms, the energies of frontier orbitals, total electronic energy Ɛ0, enthalpy ΔH°f, and free energy ΔG°f of fourteen possible structural units with sulfonic or phosphonic group in these two resins and their interaction with Cd(II) ion. The hydration of Cd(II) ion was considered during the simulation of the interaction of Cd(II) ion with the structural units. The calculation results of the electronic properties were of more reasonable significance of physics when simulating with HF method compared to B3LYP DFT method. HF method is a more suitable and reliable electronic structure theory for analyzing metal ion adsorption systems. The major reaction of Cd(II) ion adsorption onto G-26 and MTS9570 resins was presented.