Adsorption Of Cadmium By The Modified Polyvinylidene Flouride Chelating Membrane

In this research,the polyvinylidene fluoride(PVDF)-based functionalized chelating membrane(EDTMPA-TBOT/A-PVDF)was prepared with reagents of ethylenediamine tetramethylenephosphonic acid(EDTMPA),tetrabutyl orthotitanate(TBOT)and alkaline treated PVDF(A-PVDF).Then,removal of Cd(II)from aqueous solution by this membrane was studied.The Density functional theory(DFT)calculations were used to illustrate the interaction between A-PVDF and EDTMPA-TBOT.The DFT reactivity parameters,i.e.,chemical potential(μ),electronegativity(χ)and electrophilicity(ω)were calculated to explore the chemical reactivity of the above-mentioned reagents.The morphology,chemical component and functional groups of this chelating memebrane were characterized by means of scanning electron microscopy(SEM),energy spectrum analysis(EDS),Fourier transform infrared spectrum(FTIR)and X-ray photoelectron spectroscopy(XPS).The effects of pH,initial Cd(II)concentration,temperature,thicknesses of the membrane stack and flow rate,the coexisting Pb(II),Cu(II)and Ca(II),as well as citrate,nitrilotriacetic acid and ethylenediaminetetraacetic acid on the Cd(II)adsorption by the membrane were evaluated.The adsorption kinetics,adsorption isotherms,thermodynamics,breakthrough curves of the chelating membrane toward Cd(II)at the presence of above-mentioned coexisting substances and reuse performance of the chelating membrane were also investigated.The results indicate that poly(amino phosphonic acid)and A-PVDF are compatible,and the interaction between A-PVDF and EDTMPA-TBOT is enhanced compared with that of unbasified polymer.The presence of cations and complexing reagents reduces the uptake of chelating membrane toward Cd(II).The negative effect of three cations on Cd(II)adsorption follow a sequence of Pb(II)>Cu(II)>Ca(II);interferences of three complexing reagents are in the order:ethylenediaminetetraacetic acid>nitrilotriacetic acid>citrate.The isotherm data excellently fits to Langmuir model.Pseudo-second-order is competent for the description in adsorption kinetics.The negative value ofΔG~0 andΔH~0shows that adsorption of Cd(II)onto chelating membrane is spontaneous and endothermic.The adsoroption/desorption experiment indicates that the chelating membrane exhibits an excellent property of reuse.In addition,low thickness of membrane stack will be saturated in a short time,and with the increase of thickness of membrane stack the length of influent passes through also increases which results in the increasing in breakthrough time.The breakthrough time decrease with the increasing flow rate.This behavior may be due to insufficient residence time of the solute in the chelating membrane,which will cause the Cd(II)solution leaving the membrane before equilibrium occurs.When the initial Cd(II)concentration increased,the time of breakthrough point decreases and the breakthrough curves become much steeper.The equilibrium is attained faster for higher initial Cd(II)concentration,which would be anticipated with the basis of increasing driving force for mass transfer.The concentration of Cd(II)on the sectional surface of the chelating membrane aganist time shows a S-shaped feature.The simulation of continuous adsorption process indicates that the concentration gradient of Cd(II)on the chelating membrane gradually decrease with the increase of time until the membrane stack is saturated.