Magnetic Diazonium Functionalized-reduced Graphene Oxide Hybrid As An Adsorbent For Removal Of Chlorophenols From Aqueous Solution

Graphene is an excellent two-dimensional(2D)material and is applied in diverse fields.However,graphene sheets trend to aggregate in liquid phase,and are difficult to separate from solution.Hence,functionalization of graphene has achieved an appreciable accomplishment to improve the physico-chemical properties of graphene.In this work,magnetic diazonium functionalized-reduced graphene oxide(M-DF-RGO)hybrid was synthesized by a three-pot reaction and its properties were characterized.The adsorption of M-DF-RGO for 4-chlorophenol(4-CP)and 2,4-dichlorophenol(2,4-DCP)was explored.The main contents of this study were:(1)Magnetic hybrid nanomaterial,which contains magnetite(Fe3O4)particles and diazonium functionalized-reduced graphene oxide(DF-RGO),was fabricated by a three-pot reaction.First,the reduced graphene oxide(RGO)was synthesized via a redox reaction.Second,diazonium functionalized-RGO was prepared by a feasible chemical reaction.Third,Fe3O4 particles were loaded to the surface of DF-RGO by covalently bonding and M-DF-RGO hybrid was fabricated.(2)The fabricated hybrid was characterized by SEM,TEM,AFM,XRD,XPS,FT-IR,TGA,Raman spectroscopy,and magnetometer.The resulting M-DF-RGO hybrid consists of monolayer DF-RGO and Fe3O4 nanoparticles,and the number of sp2 carbon atoms increased in comparison with GO.(3)For each kind of chlorophenol(4-CP and 2,4-DCP),adsorption capacity rapidly decreased at pH>pKa.The reason for this is that chlorophenol neutral molecules mostly dissociated to anions,which would exhibit an electrostatic repulsion with the negatively charged surface of the adsorbent.The adsorption equilibrium times were short due to the single sheet structure of M-DF-RGO with good dispersity in water,which enables the adsorbate to fully contact with the plane of the adsorbent.It was found that Freundlich model was more suitable to describe the CP adsorption of M-DF-RGO and multilayer heterogeneous adsorption is dominant.(4)Density functional theory calculations indicted the ?-? interaction played an important role in the removal of chlorophenols,and the adsorbed amounts of 2,4-DCP was higher than that of 4-CP,suggesting that the number of substitutes would significantly influence donor/acceptor strength,and chlorophenol with more substituted groups had a higher adsorption capacity.(5)The recycle experiment showed that M-DF-RGO can be easily separated from aqueous solution under an external magnetic field for 2 seconds,which evidently results from a high load of Fe3O4 on the surface of M-DF-RGO.Adsorption capacity of the regenerated M-DF-RGO was still over 80%until after five cycles.Benefiting from the combined advantages of DF-RGO and Fe3O4 nanoparticles,the M-DF-RGO composite not only possessed relatively high adsorption efficiency for chlorophenols,but also could be easily separated by an external magnetic field in a fairly short time.All of these results indicated that M-DF-RGO can be utilized as an ideal adsorbent for the simple and rapid removal of phenolic pollutants from aqueous solution.