Adsorption investigation of MA-DTPA chelating resin for Ni(II) and Cu(II) using experimental and DFT methods

Melamine-diethylenetriamine pentaacetic acid (MA-DTPA) chelating resin was synthesized via the amide bond reaction between DTPA carboxyl groups and melamine amine groups. The adsorption performance of MA-DTPA resin towards Ni(II) and Cu(II) was investigated. FTIR and NMR measurements were carried out for characterization of the pristine resin and metal loaded resin. Chelating mechanism of MA-DTPA towards Ni(II) and Cu(II) has been studied using density functional theory together with a continuum solvation model. The geometrical parameters, energetic characteristic and charge population were also discussed, and then the complexation energies and complexation Gibbs free energies were calculated. The results indicate that the resin shows high affinity for heavy metal cations, and its adsorption performance of Cu(II) is better than that of Ni(II). FTIR and NMR spectra evidence the formation of amide groups and suggest that the carboxylic oxygen atoms may dominate in the coordination reaction. DFT calculations confirm that the coordination between carboxylic oxygen atom and metal cations is more favorable than that of amide nitrogen. MA-DTPA resin exhibits stronger binding capability for Cu(II) as compared to Ni(II).