Preparation Of Polyamide-amine Modified PVDF Membrane And Study On Copper Ion Adsorption

Polyamidoamine(PAMAM)is dendrimer with a large number of amine-terminated groups,highly geometrical symmetry of molecular structure and cavity inside the molecule.It adsorbs heavy metal ions by chemical adsorption and physical adsorption.Polyvinylidene fluoride(PVDF)is widely used in water treatment because of its high temperature resistance,chemical resistance,toughness and impact resistance.In this paper,PAMAM was used as the adsorbent and PVDF was used as the carrier.The adsorption mechanism of PAMAM adsorbing copper ions(Cu2+)was studied.PAMAM was added to PVDF membrane by blending or surface grafting and the composite separation membranes owned the removing Cu2+ ability.PAMAM was synthesized,and its structure was complete and the particle size was uniform.It was showed that the first adsorption happens was chemisorption when Cu2+ entered PAMAM,Cu2+ reacted with primary amines and the outermost of tertiary amines forming[Cu(NH2)2(NR)2]2+.After the coordination of the tertiary amine was completed,the remaining primary amine and the outermost amide forming[Cu(NH2)2(CONH)2]2+,after which the internal tertiary amine and amide were sequentially generated with Cu2+ forming[Cu(NR2)2(CONH)2]2+.When the concentration of Cu2+ was continuously increased,flocculent precipitation occured in the solution,at which time[Cu(NH2)4]2+ coordination occuring.At the same time,there was the embedding of Cu2+ by the internal cavity of PAMAM.PAMAM was added to PVDF by blending to prepare PVDF/PAMAM membrane.It was showed that the addition of PAMAM did not destroy the stPVDF ructure of PVDF membrane and effectively improved the hydrophilicity of membrane.The pure water flux of PVDF/PAMAM membrane was increased from 64.86 L·m-2·h-1 to 211.74 L·m-2·h-1,and the amount of copper ion adsorption was increased from 2.60 mg/g of pure membrane to 22.65 mg/g.By fitting the adsorption kinetics model,it was concluded that the adsorption of Cu2+ by PVDF/PAMAM membrane was in line with the quasi-secondary kinetic model,what was,the tendency to chemisorption.The PVDF-g-PAA graft separation membrane was prepared by grafting acrylic acid onto the PVDF membrane as the base membrane.PVDF-g-PAA-PAMAM membrane was prepared by grafting different generations PAMAM onto the surface of PVDF-g-PAA membranes.Studies had shown that PAMAM was successfully grafted onto the surface of PVDF-g-PAA membrane,and its hydrophilicity was significantly improved.The initial contact angle was reduced from 91.20° of pure PVDF membrane to 36.70°,and the pure water flux was increased from 199.00 L·m-2·h-1 to 502.38 L·m-2·h-1.It effectively improved the ability of pure membrane to adsorb Cu2+.The PVDF-g-PAA-G3.0 PAMAM membrane had the best adsorption performance,and the amount of Cu2+ adsorbed can reach 100.98 mg/g,which was higher 31.55 times than that of pure membrane 3.20 mg/g.At the same time,the desorption experiment showed that the PVDF-g-PAA-PAMAM membrane can be recycled,maintaining a high adsorption amount,and the regeneration rate was higher than 90%,and there was a possibility of industrial application.