Preparation Of Graphene Oxide/magnetic Bead Composite Adsorbent And Its Adsorption Of Hg(Ⅱ)

Graphene oxide is a sheet nanophase material which is two-dimensional structure.The surface and edge of graphene oxide contain abundant functional groups,such as,hydroxy,carboxy and epoxy etc which is a good adsorption material that have good adsorption capacity for mercury-containing wastewater.But it is difficult to separate from treated water after adsorption,In order to solve this problem,in this study,a new graphene oxide/magnetic bead(MCGO)composite adsorbent is prepared by wrapping GO on the surface of magnetic bead which are enwarpped by chitosan.The optimum preparation condition of MCGO is studied by orthogonal test and MCGO was characterized by scanning electron microscope,diffuse reflectance infrared Fourier transform spectroscopy,X-ray photoelectron spectroscopy and X-ray diffraction analyses.The adsorption property of MCGO was studied by the static adsorption experiment,such as the impact on the initial concentration,the dosage of adsorbent,adsorption time and temperature,the value of pH,ionic strength and coexist anion and cation.The adsorption kinetics,thermodynamics,Hg(Ⅱ)removal mechanism and the capacity of cyclic regeneration were also studied.The main conclusions were as follows:(1)Graphene oxide/magnetic bead composite adsorption material was synthesized by warpping GO on the surface of magnetic bead which rely on the method of cross-linked chitosan.The optimum preparation condition of MCGO for adsorption of Hg(Ⅱ)was determined by orthogonal test: GO(15 mL),the concentration of chitosan(4.0%),the dosage of epichlorhydrin(0.5 mL),cross-linked temperature(30℃).Through X-ray diffraction analyses,it can be seen that magnetic bead contain magnetic hematite whose component is γ-Fe2O3,therefore,magnetic bead has magnetic properties;scanning electron microscope indicated that magnetic bead with globular fine particles and loose irregular vitreous bodies becomed rough surface with wrinkles after loading GO.MCGO was characterized in the way of diffuse reflectance infrared Fourier transform spectroscopy,compared with magnetic beads,The new elements of C,N and vibrational absorption peak C-O,C-N and N-Hon the surface of MCGO indicated that GO had been successfully grafted on the magnetic beads.(2)The adsorption property of MCGO was studied by adsorbing low concentration of mercury solution.The adsorption effect of MCGO for Hg(II)increased with the increase of adsorption time and adsorption temperature.The removal rate of MCGO for Hg(II)increased firstly and then decreased in the range of2~12 and the adsorption effect is the best when the value of pH is 7.19.The effect of ionic strength is not obvious.Fe3+and Pb2+ can inhibited the adsorption of MCGO for Hg(II)in coexisting cation.The effect of coexisting anions had a general trend that was to promote the adsorption of MCGO for Hg(II).(3)The adsorption of MCGO for Hg(II)reached the adsorption equilibrium in 2h.The adsorption process accorded with the pseudo two order kinetics model and the adsorption thermodynamics accorded with Freundlich adsorption isotherm model.The value of ΔH0 is 4.294 kJ/mol,the value of ΔG0 is from-0.394 kJ/mol to-0.944kJ/mol and the value of ΔS0 is 15.731 J/(mol·K),which showed that the adsorption was an endothermic,spontaneous and entropy increasing process.(4)The fitting of kinetic model and isotherm model indicated that the adsorption process was not a monolayer adsorption but physical and chemical adsorption.However,the characterization of DRIFT and XPS before and after the adsorption of Hg(II)by MCGO showed that the adsorption mechanism was electrostatic attraction and complexation.(5)Desorption capability is studied by 0.1 mol/L thiourea and 0.2 mol/L HCl solution which are the same volume to blend as desorption agent.The desorption arrives to balance when the desorption time reaches 18 h.The value of desorption rate was 85.69% after desorption of 24 h.The desorption process accorded with parabolic equation indicated that desorption process was a diffusion controlled process.The removal rate of MCGO for Hg(II)was 40.97% after 4 times of recycling MCGO which indicated that MCGO still had a certain degree of re-adsorption capacity.