Preparation Of PAMAM Functional Materials And Its Adsorption Properties For Heavy Metal Ions

In recent years,the adsorption method has been recognized as an effective means of removing heavy metal ions that pose a serious threat to organisms due to its sim-plicity and high economic benefits.Dendritic macromolecules are a class of polymer molecules with dendritic structure.Polyamidoamine（PAMAM）,as one of the most representative dendritic macromolecules,possesses regular and symmetrical struc-tures,controllable molecular weights,and abundant amino groups and cavities inside and outside the structure.Therefore,PAMAM has been widely utilized in researches due to its ability to adsorb and remove heavy metal ions through physical and chemi-cal processes.However,the high water solubility of PAMAM precludes its direct use in the adsorption and removal of heavy metal ions.This study presents a suitable car-rier for preparing modified PAMAM adsorbents that facilitate the easy adsorption and separation of heavy metal ions,which improves the adsorption capacity of the adsor-bent while simultaneously solving the application problem of PAMAM.The hyperbranched PAMAM（G1 PAMAM～G4 PAMAM）was synthesized via divergent synthesis,which involved alternating amidation and Michael addition reac-tions using ethylenediamine and methyl acrylate as raw materials.To address the issue of high solubility of PAMAM,PVDF-g-PAA powder was synthesized via grafting acrylic acid（AA）onto polyvinylidene fluoride（PVDF）powder after alkali treatment,and subsequently transformed into a PVDF-g-PAA plate membrane with phase trans-formation method.PVDF-g-PAMAM hyperbranched modified membranes were pre-pared by grafting various generation of PAMAM onto PVDF-g-PAA plate membranes.Additionally,their structures and adsorption capabilities of heavy metal ions were in-vestigated.The results demonstrated that PAMAM grafted onto PVDF membrane could significantly increase the hydrophilicity of the membrane.With an adsorption capacity of 113.7 mg/g,which was 10.7 times higher than that of pure PVDF mem-brane,the PVDF-g-G3 PAMAM membrane demonstrated the highest ability to adsorb Cu²⁺among them.The pseudo-second-order kinetic model and the Langmuir iso-thermal adsorption model both agreed with the adsorption behavior of Cu²⁺.Further-more,the membrane also performed well in terms of recycling.To simplify the grafting process,a PDA layer was formed on the surface of a flat membrane which scraped with PVDF through the oxidation crosslinking self-polymerization reaction of dopamine（DA）and the adhesion of polydopamine（PDA）.Different generations of PAMAM were grafted onto the surface of PVDF/PDA membrane to prepare PVDF/PDA-g-PAMAM membranes by the cross-linking reaction between PDA and PAMAM.The results showed that PAMAM could significantly improve the hydrophilicity of the membranes.The PVDF/PDA-g-G3 PAMAM membrane showed the best Cu²⁺adsorption capacity of128.0 mg/g,which was 12.1 times higher than that of pure PVDF membranes,and the modification effect was better than that of PVDF-g-PAA.Moreover,The adsorption behavior of Cu²⁺was consistent with the pseudo-second-order kinetic model and Langmuir isothermal adsorption model,and had an excellent recycling performance.Due to the porosity nature of the hydrogel and its purpose as the carrier of PA-MAM,heavy metal ions adsorption capacity of the adsorbent was improved.The physically crosslinked CTS/PAMAM/SA/Ca²⁺double network hydrogel was prepared by semi-dissolved acidizing sol-gel transformation method that using chitosan（CTS）grown in situ with different generations of PAMAM as substrate under the action of gluconolactone.The results showed that the CTS/G3 PAMAM/SA/Ca²⁺hydrogel had the best comprehensive performance,and the adsorption capacities of Cu²⁺and Cd²⁺reached 145.5 and 127.7 mg/g,respectively,which were 1.56 times and 1.53 times higher than that of CTS/SA/Ca²⁺hydrogel.The adsorption behaviors of Cu²⁺and Cd²⁺were consistent with the pseudo-second-order kinetic model and Langmuir isothermal adsorption model.Moreover,the hydrogel had a priority for adsorption and removal of Cu²⁺.In addition,the adsorption cycle test results showed that the hydrogel had a good recycling performance.On this basis,the CTS/PAMAM/ATP hydrogel was prepared by mixing atta-pulgite（ATP）into the hydrogels prepared by semi-dissolved acidizing sol-gel trans-formation method,which not only improved the adsorption capacity of heavy metal ions on the hydrogel adsorbent,but also met the problems of dispersivity and recy-cling in the using of ATP.The results showed that CTS/G3 PAMAM/ATP had the best comprehensive performance,and its adsorption capacity for Cu²⁺and Cd²⁺reached168.30 and 144.20 mg/g respectively,which was 1.40 and 1.41 times higher than that of CTS/ATP hydrogel.The adsorption behavior of Cu²⁺and Cd²⁺were consistent with the pseudo-second-order kinetic model and Langmuir isothermal adsorption model.In addition,the hydrogel adsorbed and removed Cu²⁺preferentially.Additionally,the hydrogel had a good recycling performance,as evidenced by the results of the adsorp-tion cycle test.