Judicious Fabrication Of Bifunctionalized Graphene Oxide/MnFe₂O₄ Magnetic Nanohybrids For Enhanced Removal Of Pb（Ⅱ）、Cu（Ⅱ） From Water

The treatment of water heavy metal pollution is quite challenging,which is a heated issue in the field of environmental research.Adsorption method is regarded as one of the effective methods to solve these kind of problems,and various adsorption materials have emerged accordingly.Graphene oxide-based adsorption materials have attracted extensive attention due to their large specific surface area and outstanding adsorption properties.Currently,various modification researches on graphene oxide（GO）emerge one after another.However,the modification of single functional group fails to make full use of the rich active functional groups on its surface.Meantime,the adsorption material is not easy to recover,and the problem of secondary pollution is serious,which limits the further development of graphene materials.To achieve the full adsorption potential of GO and solve the problem of difficult adsorbent recovery,in this study,functional groups,amino and Phosphoric acid groups,were introduced into GO and coupled with Mn Fe₂O₄ nanoparticles to prepare novel ternary nanohybrid materials.Firstly,GO was prepared by the improved Hummers method,and then the Phosphate-based functionalized graphene oxide（Phos-GO）was prepared by replacing hydroxyl groups on GO surface with Phosphate groups under nitrogen.Finally,PHEA and magnetic nanoparticles（Mn Fe₂O₄）were chemically grafted onto Phos-GO by hydrothermal method to generate PEHA-PHOS-GO/Mn Fe₂O₄.Scanning electron microscope（SEM）,transmission electron microscope（TEM）,Fourier transform infrared spectrum（FT-IR）,X-ray diffraction spectrum（XRD）,X-ray photoelectron spectrum（XPS）,Zeta potential and hysteresis loop（VSM）were employed to observe the surface morphology and composition of active functional groups of the adsorbent.Pb（Ⅱ）and Cu（Ⅱ）were selected as the target adsorbates to study the adsorption performance of PEHA-PHOS-GO/Mn Fe₂O₄ at different initial p H values,initial heavy metal ion concentrations,contact time and reaction temperature.The results show that PEHA-PHOS-GO/Mn Fe₂O₄shows high removal efficiency and rapid magnetic separation of Pb（Ⅱ）and Cu（Ⅱ）due to a large number of amino and Phosphoric acid groups on the bifunctional functionalized graphene oxide nanosheets and magnetic nanoparticles of Mn Fe₂O₄.When the optimal adsorption p H is 5.5,the reaction temperature is 303 K,and the initial concentration of heavy metal ions is 100 mg/L,the maximum adsorption capacities of PEHA-Phos-GO/Mn Fe₂O₄ to Pb（Ⅱ）and Cu（Ⅱ）are 366.4 and 167.6 mg/g respectively,which are much higher than GO（212.1 and 75.0 mg/g）.Adsorption kinetics and isotherm fitting data show that the adsorption process can be well described by quasi-second-order kinetics and Langmuir model,which indicates that the adsorption of heavy metal ions by PEHA-Phos-GO/Mn Fe₂O₄ is mainly chemical adsorption and single-layer adsorption on uniform surface.Thermodynamic studies show that the adsorption of Pb（Ⅱ）and Cu（Ⅱ）by composite PEHA-Phos-GO/Mn Fe₂O₄is a spontaneous endothermic process and belongs to chemical adsorption.After four adsorption-desorption cycles,PEHA-Phos-GO/Mn Fe₂O₄ still maintained a high recovery rate.This research provides both theoretical and practical foundations for further nanohybrid study.