Removal Of Heavy Metal Ions In Water By Hyperbranched Polyamide-amine Grafted Graphene Oxide-Nanofiltration Combined Technology

Adsorption is one of the ideal methods to remove heavy metal ions in water.However,the adsorption efficiency of traditional adsorbents is relatively low,which limits their applications.Nano-adsorption materials have attracted much attention as an adsorption material with large adsorption area and high adsorption efficiency.However,the nano-adsorbent also has potential environmental risks,because its particle size is small,and it is difficult to separate after the adsorption is completed,causing it to leak into the environment.In this study,a nano-adsorbent was used in combination with a nanofiltration membrane to remove heavy metal ions in water.First,a nanofiltration membrane was formed on the surface of a polyethersulfone hollow fiber ultrafiltration base membrane by an interfacial polymerization method,and six factors that considered to be possible for affecting the reaction process are included in the experiment to get the best condition of the interface reaction process,the concentration of the monomer in the water phase,the coating time of the water phase,the concentration of the monomer in the organic phase,and the reaction time in the interface,purge time,and the effects of additives in the water phase.Meanwhile,the nanofiltration membranes prepared by the optimal preparation process were characterized by FTIR,SEM and AFM,and their rehection properties were characterized by the rejection of heavy metal ions,inorganic salts,dyes,proteins,and polyethylene glycol.The results show that the water flux of the prepared hollow fiber nanofiltration membrane is about 17.2L/（m²·h）,and the rejection of inorganic salts is as follows:R（Na2SO4）>R（Mg SO4）>R（Mg Cl2）>R（Na Cl）,The rejection rate for methyl orange is about94%,and the retention rate for rhodamine B is about 89%.The rejection rates of nanofiltration membranes for Cu²⁺,Cr³⁺and Pb²⁺were 89%,90%and 93%,.Then,under basic conditions,1-（3-dimethylaminopropyl）-3-ethylcarbodiimide hydrochloride（EDC）was used to graphene oxide（GO）and hyperbranched polyamide-amine（HPAMAM）reaction to synthesize supported hyperbranched polyamide-amine graphene oxide（HPAMAM-GO）.The structure and morphology of HPAMAM-GO were characterized by FTIR,XPS,XRD and TEM characterization.The effects of initial concentration,p H,time,and number of repetitions on the adsorption capacity of HPAMAM-GO were also explored in the experiment.Through experimental research,it was found that the adsorption process of Cu²⁺by HPAMAM-GO conforms to the Langmuir model and quasi-second-order kinetic model,and is a single-molecule adsorption process dominated by chemical adsorption.Finally,in this study,the removal rates of four heavy metal ions,Cu²⁺,Cr³⁺,Pb²⁺,and Ag⁺,were measured by combining the prepared HPAMAM-GO nanosorbent with a nanofiltration membrane to be 98.7%,99.1%,99.5%,and 99.3%,respectively.Taking copper ions as representative heavy metal ions,the removal effects of hollow fiber nanofiltration membrane,HPAMAM-GO adsorbent,and HPAMAM-GO-nanofiltration technology were investigated,and the removal of copper ions by HPAMAM-GO-nanofiltration technology was found.The effect is higher than using nanofiltration membrane and adsorbent alone.Among them,the main contribution to the removal of heavy metal ions comes from the adsorbent.The nanofiltration membrane can not only trap the nano-adsorbent,but also further trap the heavy metal ions in the aqueous solution that are not adsorbed by the adsorbent.