Coupling Magnetism To Graphene Oxide Derived Materials And Application For Adsorption Of Heavy Metal Ions From Multicomponent Systems

Graphene oxide has received world-wide attention due to its exceptional physicochemical properties,but it has the disadvantages of harder solide-liquid separation and low adsorption capacity.Therefore,the solid-liquid separation ability of graphene oxide should be improved by attaching some magnetic materials,and the adsorption ability should be enhanced by grafting new functional groups.It is well known that organic substances and electrolytes usually co-exist with metal ions in wastewater.The organics and electrolytes can influence the removal of metal ions.Therefore,it is important to investigate the influence mechanism of or organics and background electrolytes on the metal ions adsorption.In this study,derived materials with advantages of easy solide-liquid separation and high adsorption capacity were synthesized from graphene oxide and were used as adsorbents for removing metal ions from aqueous solution.The influence mechanism of organics and background electrolytes on the metal ions adsorption by these derived materials was investigated.The specific research work and the study results can be summarized in the following five sections:The first section focused on the preparation of a sulfonated magnetic graphene oxide（SMGO）from graphene oxide,and this derived material was used as adsorbent for removing Cu（Ⅱ）ions from aqueous solution.The derived material was characterized by TEM,EDS,Particles size,BET,TG-DTA,FT-IR,Raman,XRD,and VSM.It can be separated and recovered easily using magnetic separation technology.The effects of operating parameters such as pH,Cu（Ⅱ）concentration and temperature on the Cu（Ⅱ）adsorption were investigated by using a response surface methodology（RSM）.Optimum Cu（Ⅱ）uptake of 62.73 mg/g was achieved at pH 4.68,Cu（Ⅱ）concentrations 73.71 mg/L,and temperature 50 ℃.The adsorption process can be well described by the pseudo-second order kinetic model.The experimental data of isotherm followed the Langmuir isotherm model.Moreover,the thermodynamic parameters calculated from the temperature-dependent isotherms indicated that the adsorption reaction was an endothermic and spontaneous process.All results indicate that the SMGO is a promising adsorbent for the efficient removal of copper ions from wastewater（chapter 2）.The second section studied the mutual effects of Cd（Ⅱ）and aniline adsorption on sulfonated magnetic graphene oxide（SMGO）.The effects of operating parameters such as pH,adsorbent dosage,aniline concentration,ionic strength,contact time and temperature on the Cd（Ⅱ）enrichment,as well as the adsorption kinetics and isotherm were also investigated.The results demonstrated that SMGO could effectively remove Cd（Ⅱ）and aniline from the aqueous solution and the two adsorption processes were strongly dependent on solution pH.The Cd（Ⅱ）adsorption was reduced by the presence of aniline at pH<5.4,but was improved at pH>5.4.The presence of Cd（Ⅱ）diminished the adsorption capacity for aniline at pH<7.8 but enhanced the aniline adsorption at pH>7.8.The decontamination of Cd（Ⅱ）by SMGO was influenced by adsorbent dosage,aniline concentration,and ionic strength.Besides,the adsorption process could be well described by pseudo-second-order kinetic model.The intraparticle diffusion study revealed that the intraparticle diffusion was not the only rate-limiting step for the adsorption process.Moreover,the experimental data of isotherm followed the Freundlich isotherm model（chapter 3）.The third section investigated the influence mechanisms of background electrolytes and ionic strength on Cd（Ⅱ）removal,the adsorption of Cd（Ⅱ）onto the sulfonated magnetic graphene oxide（SMGO）in aqueous solutions containing different types and concentrations of background electrolytes was studied.The results indicate that Cd（Ⅱ）adsorption was strongly dependent on pH and could be strongly affected by background electrolytes and ionic strength.The Cd（Ⅱ）removal was decreased with the presence of background electrolyte cations(Na⁺,K⁺,Ca²⁺,Mg²⁺,Mn²⁺,Zn²⁺,and Ni²⁺),and the divalent cations exerted more obvious influences on the Cd（II）uptake than the monovalent cations at pH 6.Both Cl^- and NO₃^- had negative effects on Cd（Ⅱ）adsorption because they can form water-soluble metal-anion complexes with Cd（Ⅱ）ions.The presence of 0.01 M Na₃PO₄ reduced the removal percentage of Cd（Ⅱ）at pH<5 but extremely enhanced the Cd（Ⅱ）removal when the pH>5.The Cd（Ⅱ）adsorption was sensitive to changes in the concentration of NaCl,NaNO₃,NaClO₄,and Na₃PO₄.Besides,the adsorption isotherm of Cd（Ⅱ）onto SMGO could be well described by the Freundlich model and was also influenced by the type of background electrolyte ions and the ionic strength（chapter 4）.In the fourth section,the aminated magnetic graphene oxide（AMGO）was synthesized and characterized by FESEM,TG-DSC,XRD,VSM,and XPS.The effects of organic acid（sodium acetate,sodium benzoate,and sodium oxalate）and background electrolytes（NaNO₃,KNO3,NH₄·NO₃,Ca（NO₃）₂,Mg（NO₃）₂,Zn（NO₃）₂）on the adsorption behavior of Cu（II）by AMGO were investigated.The results showed that Cu（Ⅱ）adsorption could be affected by electrolytes and organic acid.The Cu（Ⅱ）adsorption was increased as the concentrations of sodium acetate,sodium benzoate,and sodium oxalate increased from 0 mM to optimal value（from 0 mM to 0.2 mM for sodium acetate,from 0 mM to 0.6 mM for sodium benzoate and sodium oxalate）at pH 5.5,while decreased slightly with further increasing organic acid concentrations.The presence of NaNO₃,KNO₃,NH₄·NO₃,Ca（NO₃）₂,Mg（NO₃）₂,Zn（NO₃）₂ enhanced the Cu（Ⅱ）removal slightly.The presence of 0.01 M Ca（NO₃）₂ and 0.1 mM sodium benzoate effected the adsorption kinetics of Cu（Ⅱ）,and the adsorption kinetics data were found to follow the pseudo-second-order rate equation.Besides,the adsorption rate was controlled by film diffusion and intraparticle diffusion.The adsorption data showed good correlation with the Langmuir and Temkin isotherm models.In the three systems,the maximum adsorption capacities obtained from the Langmuir model were 155.86 mg/g（without organic acid and background electrolytes）,152.25 mg/g（with addition of 0.01 M Ca（NO₃）₂）,176.88 mg/g（with presence of 0.1 mM sodium benzoate）,respectively（chapter 5）.The fifth section evaluated the effects of six inorganic electrolyte anions on Cu（Ⅱ）removal using the aminated magnetic graphene oxide（AMGO）in single-and multi-ion systems.A 2^6-2 fractional factorial design（FFD）was employed for assessing the effects of multiple anions on the adsorption process.The results indicated that the Cu（Ⅱ）adsorption was strongly dependent on pH and could be significantly affected by inorganic electrolyte anions due to the changes in Cu（Ⅱ）speciation and surface charge of AMGO.In the single-ion systems,the presence of monovalent anions（Cl^-,ClO₄^-,and NO₃^-）slightly increased the Cu（Ⅱ）adsorption onto AMGO at low pH,while the Cu（Ⅱ）adsorption was largely enhanced by the presence of SO₄^2-,CO₃^2-,and HPO₄^2-.Based on the estimates of major effects and interactions from FFD,the factorial effects of the six selected species on Cu（Ⅱ）adsorption in multi-ion system were in the following sequence:HPO₄^2->CO₃^2->Cl->SO₄^2->NO₃^-= ClO₄^-,and the combined factors of AD(Cl-× SO₄^2-)and EF(CO₃^2-×HPO₄^2-)had significant effects on Cu（Ⅱ）removal（chapter 6）.