Adsorption Investigation Of The Modified Polyvinylidene Fluoride Chelating Membrane Towards Nickel Ions

Using the covalent bonding reaction between melamine (MA) anddiethylenetriaminepentaacetic acid (DTPA), and the solution blending and phaseinversion technique, a kind of novel polyvinylidene fluoride (PVDF)-based chelatingmembrane was prepared. The modified chelating membrane bearingpolyaminecarboxylate groups was used to remove Ni(II) in different forms from thewastewater.The membrane was characterized by SEM and FTIR techniques. The effects of thecoexistent Ca(II) cation and lactic acid on the Ni(II) uptake of the chelating membranewere studied. Quantitative adsorption experiments were performed for elucidating theadsorption characteristics regarding the presence of coexistent cation and the organic acid.FTIR result suggests the polyaminecarboxylate groups have been blended to thechelating membrane successfully and the chelation dominates in the Ni(II) adsorption.The chelating membrane exhibits significant adsorption towards the hydrated Ni(II) withthe uptake above0.030mg/cm2. Although the coexistent Ca(II) and lactic acid reduceNi(II) adsorption of the chelating membrane, do they not alter the adsorption nature ofthe membrane. The batch adsorption results show that the sorption kinetics fit well toLagergren second-order equation and the isotherms can be well described by Langmuirmodel. D-R plots indicate the ion exchange mechanism of the adsorption process. Thethermodynamic parameters ΔG0<0、ΔH0<0、ΔS0>0, demonstrate the spontaneous andexothermic nature of adsorption. The adsorption/desorption experiment indicates that thechelating membrane possesses excellent property of reuse.The reaction mechanism between MA and DTPA in the organic solvents wasexplained based on the ab initio theory from the molecular level. Density functionaltheory (DFT) was adopted to explore the adsorption characteristics of the chelatingmembrane towards Ni(II). The coordination structures of MA-DTPA ligand with Ni(II)were optimized and the stable configurations were obtained by analyzing the optimizedgeometrical parameters, the complexing energy and charge population. The geometry optimizations were performed for Ni(II)-lactic acid and Ca(II)-MA-DTPA complexes.The complexation energies, Gibbs free energies and charge population have beencalculated to determine the complexing stability. DFT calculations show that thestabilities of Ca(II)-MA-DTPA ligand and Ni(II)-lactic acids can not be comparable tothat of Ni(II)-MA-DTPA, which is consistent with the experimental results.