Adsorption Investigation Of APTMS-DTPA/PVDF Chelating Membrane Towards Copper Ions

Using the solution blending and phase inversion techniques, diethylenetriaminepentomic acid, polyvinylidene fluoride and3-aminopropyltrimethoxysilane were used toprepare a polyvinylidene fluoride (PVDF)-based chelating membrane, i.e.,3-aminopropyltrimethoxysilane-diethylenetriaminepentaacetic acid/polyvinylidenefluoride (APTMS-DTPA/PVDF) chelating membrane. Then, this chealting membrane wasemployed to remove Cu(II) from the solutions, considering the existences of Ni(II), Co(II),tartrate and ethylenediaminetetraacetic acid (EDTA).The influences of Ni(II), Co(II), tartrate and ethylenediaminetetraacetic acid (EDTA)on the chelating membrane towards Cu(II) were investigated, and both static and dynamicadsorption experiments were carried out. The conventional kinetic equations,thermodynamic equations, and the bed depth service time (BDST) model were adopted toanalyze the experimental data of static adsorption and breakthrough curves, respectively.The APTMS-DTPA/PVDF membrane has an excellent performance for the adsorption ofthe hydrated Cu(II), and the maximum adsorption capacity of Cu(II) can reach to0.213mg/cm2. The coexistent cations interfere with the Cu(II) adsorption in the order ofNi(II)> Co(II), and the complexing capability of the organic acid is in the order ofethylenediaminetetraacetic acid> tartrate acid. The results of dynamic adsorption, andthermodynamic adsorption experiments fit the Lagergren second-order equation, andLangmuir model well. D-R plots indicate that the adsorption reaction belong to an ionexchange reaction. The thermodynamic parameters ΔG0<0, ΔH0<0, ΔS0>0,demonstrate the spontaneous and exothermic nature of the process of Cu(II) adsorption.For the breakthrough curve of Cu(II) uptake, the mass transfer rate Kaderived from theBDST model is in the order: Ni(II)<Co(II)<Cu(II); ethylenediaminetetraacetic acid <tartrate acid. Furthermore, the bed sorption capacity No on unit volume of membrane is inthe order of Ni(II)<Co(II)<Cu(II), ethylenediaminetetraacetic acid <tartrate acid. Theabove-mentioned results are consistent with that of static batch adsorption processes. Inaddition, the adsorption/desorption experiment indicates that the chelating membraneexhibits an excellent property of reuse. It should be mentioned that, in this research, the density function theory (DFT) wasemployed to reveal the adsorption properties on APTMS-DTPA/PVDF membrane towardsCu(II). The stable structure of Cu-(APTMS-DTPA/PVDF)2-was obtained by means ofanalyzing geometrical parameter. Then, the charge population and complexing energy ofNi(II)-, Co(II)-, and [Cu(APTMS-DTPA)]2-complexes were calcualted. Also, thecomplexes of Cu(II) bonding with thylenediaminetetraacetic acid and tartrate wereconsidered. The stabilities of metal-(APTMS-DTPA)2-are in the order:[Cu(APTMS-DTPA)]2->[Ni(APTMS-DTPA)]2->[Co(APTMS-DTPA)]2-, and theaffinity the chelating membrane with Cu(II) is stronger than that ofethylenediaminetetraacetic acid>tartrate acid towards Cu(II), which is in line with theexperimental results.In addition, the chemical reactivity descriptors of APTMS-DTPA ligand, Cu(II),Ni(II), Co(II), ethylenediaminetetraacetic acid and tartrate were calcualted. Comparedwith other reactants, Cu(II) and APTMS-DTPA ligand show the higher abilities ofaccepting electrons and donating electrons, respectively. The values of charge transfer,complexing energy, and Gibbs free energy of [Cu(APTMS-DTPA)]2-complex are–0.954,–382.322kJ/mol, and–592.927kJ/mol. Among the eight bonding sites of the chelatingmembrane, O18and N22atoms cannot be occupied. The [Cu(APTMS-DTPA)]2–complex will tend to exist in the form of5-coordinated geometry.