Adsorption Investigation Of The Modified Polyvinylidene Fluoride Ion Exchange Membrane Toward Cu(â…¡) And Ni(â…¡)

A kind of modified polyvinylidene fluoride (PMAA-PVDF) ion exchange membranewith the adsorption performances of heavy metals, was prepared using solution thermallyinduced polymerization and phase inversion process. The components of the cast solutionwere optimized by the orthogonality experiment. The ion exchange membrane wascharacterized using thermo analysis(TG-DSC), X-ray diffraction analysis(XRD), Fouriertransform infrared spectroscopy (FTIR), and environmental scanning electron microscopy(ESEM). The adsorption characteristic of the exchange membrane towards to Cu(Ⅱ) andNi(Ⅱ) was also analyzed using COSMO-corrected density functional theory(DFT).The influences of pH, temperature, contact time, and the concentration of Cu(Ⅱ) andNi(Ⅱ) on the performance of PMAA-PVDF ion exchange membrane were investigated inthis research. Quantitative analysis for adsorption was conducted to investigate thekinetics, adsorption isotherm and thermodynamics. The adsorption/desorption property ofthe ion exchange membrane was evaluated.The results of TG-DSC measurements indicate the membrane exhibits an excellentthermal stability. The FTIR measurement shows that the carboxylic acid functional grouphas been grafted into PVDF membrane successfully. XRD measurement reveals that thegrafting of α-methacrylic acid does not change the crystal structure of PVDF, and the ionexchange membrane has the same crystal structure as that of the pristine PVDF polymer.The results of the experiments indicate that the PMAA-PVDF ion exchangemembrane has excellent adsorption properties of Cu(Ⅱ) and Ni(Ⅱ) ions, and its adsorptioncapacity of Cu(Ⅱ) is larger than that of Ni(Ⅱ). The adsorption isotherm fits better to theFreundlich isotherm model, and the pseudo-second-order kinetics model gives a better fitto the batch sorption kinetics. The intra-particle diffusion model reveals that theadsorption process is controlled by the intra-particle diffusion process. Thermodynamicparameters, H0is less than0, G0is lower than0, and S0is greater than0, which showsthat both of the adsorption of Cu(Ⅱ) and Ni(Ⅱ) by the modified PVDF ion exchangemembrane are spontaneous and exothermic processes. The adsorption/desorption curvesof Cu(Ⅱ) and Ni(Ⅱ) indicate that the membrane can be resued. The solvation effect-corrected DFT theoretical calculations indicate the bindingenergy of Cu(MPAA-PVDF) complex is larger than that of Ni(MPAA-PVDF) complex,consistent with the results of the adsorption experiments. It can be also inferred that thewater molecule coordinated by Cu(Ⅱ) and Ni(Ⅱ) can be eliminated, when the heavy metalscoordinate the carboxyl groups of the membrane. Cu(Ⅱ) can form2-coordinated,3-coordinated and4-coordinated complex structures with PMAA-PVDF exchangemembrane, because of the space hindrance of the membrane and the repulsion effects ofthe oxygen atoms. Compared with that of Cu(PMAA-PVDF) complex, Ni(Ⅱ) favours thecomplexes involving3-,4-,5-and6-coordinated structures.