Preparation Of PAMAM Modified PVDF Membranes And Adsorption Of Heavy Metal Ions

Polyvinylidene fluoride(PVDF)is widely used in wastewater treatment as a separation membrane material because of its excellent heat resistance,acid and oxidation resistance and processing properties.Heavy metal ions pollution is an urgent environmental problems which need to be solved currently,the G3.0 PAMAM because of its highly symmetrical molecular structure,a large number of amine groups,intramolecular cavity,has excellent adsorption properties for heavy metal ions.In this paper,aiming at the problem of heavy metal ions pollution in water,PVDF membrane was taken as the research object,PAMAM was used as organic modifier,two composite membrane which use PVDF as the substrate with heavy metal ion adsorption capacity were prepared by basal membrane surface grafting and bulk graft modification.G3.0PAMAM as aqueous phase monomer was obtained by the divergent method.After a simple alkali treatment of PVDF powder,PVDF-g-PAA copolymer was synthesized by free radical polymerization.Then the PVDF-g-PAA flat menbrane which as matrix was made by the phase inversion method,PVDF-g-PAA-G3.0 PAMAM modified membrane was prepared by the surface grafting G3.0 PAMAM.Research has shown that alkali-treated PVDF did not cause damage to the basic structure of PVDF,The initial contact angle of PVDF-PAA-G3.0 membrane which significantly lower than PVDF membrane can reach 56°.The hydrophilic properties of modified membranes have been greatly improved.PAM AM occupies the pores on the surface of PVDF-g-PAA membrane after grafting on the membrane surface,but does not decrease the flux on the contrary increases greatly due to its good hydrophilicity.PAMAM is arranged neatly on the membrane surface,because of the unique chemical structure of PAMAM,a total of 16 amino groups are located in the periphery and each set of four amino groups could be considered as one-quarter branch.Then,one quarter branch could have only one reactive site,and possibly four amide bonds could be formed for one PAMAM molecule on average.In this case,the remaining 12 free "-NH2" groups have good coordination with heavy metal ions,which contributed to the high adsorption efficiency.The adsorption capacity of PVDF-PAA-G3.0 PAMAM membranc to Cd2+ and Cu2+ is much higher than that of pure PVDF film.The adsorption kinetics study showed that the adsorption mechanism in line with the pseudo-second-order kinetic model,the adsorption process is controlled by chemical adsorption.The adsorption mechanism mainly depends on the amino coordination and chelation.Langmuir constant can obtain the maximum adsorption capacity of the modified membrane for the theory of Cu2+ and Cd2+ up to 71.28mg/g,64.31mg/g.Using powder direct grafting method,the graft copolymer PVDF-g-PAA which as matrix with PVDF and AA was synthesized.PVDF-g-PAA-G3.0PAMAM graft copolymer was prepared by using it graft G3.0PAMAM,then the PVDF-g-PAA-G3.0PAMAM flat membrane was made by the phase inversion method.Compared with the PVDF membrane,the water flux of PVDF-g-PAA membrane modified increased,and which modified by PAM AM continued to increase significantly.The adsorption of PVDF-g-PAA-G3.0PAMAM membrane to Cd2+ and Cu2+ was significantly improved than the PVDF membrane.The adsorption kinetics study showed that the adsorption mechanism in line with the pseudo-second-order kinetic model,the adsorption process is controlled by chemical adsorption.The adsorption mechanism mainly depends on the amino coordination and chelation.