Adsorption Performance Of Eu（Ⅲ） Onto Funtionalized Graphene Oxide Composites In Presence Of Fulvic Acid

The radionuclide pollutions released into the natural environment are urgently concerned to scientific researchers in the world.However,the radionuclides are extremely hazardous to human body,which further restricts the related development of science researches.Fortunately,Europium（Eu（Ⅲ））possessing a strong resemblance to other detrimental trivalent elements both physical and chemical properties,can be used as safe substitute for radionuclides in various adsorption studies.Meanwhile,humic substances include humic acid and fulvic acid as an organic macromolecule,which widely exists in the natural environment and has a tremendous impact on the adsorption behavior of europium onto solid media.The influence of natural environment on adsorption of Eu（Ⅲ）cannot be ignored.In this work,the sheet graphites were oxidized using strong oxidants to make them into graphene oxide（GO）.Ca-Mg-Al LDH and carboxymethyl-β-cyclodextrin were successfully compounded with graphene oxide respectively,functionalized GO based composites were further prepared.The adsorption performances of Eu（Ⅲ）onto functionalized graphene oxide composites were investigated using batch experiments in the presence of fulvic acid,such as solution pH,ionic strength,contact time,temperature,et al.The especial changes of elements and functional groups before and after Eu（Ⅲ）onto functionalized GO composites were determined by X-ray photoelectron spectroscopy,and the adsorption mechanisms were further discussed.The adsorption mechanism of Eu（Ⅲ）in solid-liquid interfaces was detailedly elucidated.Conclusions can be obtained as follows.The maximum adsorption capacity of Ca-Mg-Al LDH/GO for Eu（Ⅲ）was 1.12×10^-3mol/g at 303 K,and then the maximum adsorption capacity of CM-β-CD/GO for Eu（Ⅲ）was1.01×10^-3 mol/g at 298 K.The increasing environmental temperature was favorable for the adsorption of Eu（Ⅲ）onto functionalized graphene oxide composites,and the adsorption rate was accordingly increased.The adsorption performance of Eu（Ⅲ）onto functionalized GO composites was spontaneous and endothermic process through thermodynamic parameters.The influences of pH and ionic strength on the adsorption behavior of Eu（Ⅲ）were further investigated.The adsorption behaviors of Eu（Ⅲ）on Ca-Mg-Al LDH/GO and CM-β-CD/GO samples were greatly affected by pH and ionic strength.The adsorption mechanisms of Eu（Ⅲ）on functionalized GO composites were dominated by outer-sphere surface complexation and/or cation exchange at pH<7.0.And then the adsorption of Eu（Ⅲ）on functionalized GO composites were contributed to the inner-sphere surface complexation at pH>7.0.The adsorption performance of Eu（Ⅲ）was further investigated under various contact time.The equilibrium contact time was about 2.5 h and 20 min for the adsorption of Eu（Ⅲ）onto Ca-Mg-Al LDH/GO and CM-β-CD/GO,respectively.Ca-Mg-Al LDH/GO and CM-β-CD/GO could reach the fast adsorption equilibrium,and the adsorption equilibrium constant k₂ of pseudo-second-order and adsorption capacity q_e were also maximum.The adsorption equilibrium time of Eu（Ⅲ）onto CM-β-CD/GO was about 20 min,indicating that the adsorption was fast in the initial stage and then the reaction rate remained high level over long time.The above adsorption reaction kinetics could be described by pseudo-second-order kinetic models.The adsorption performance of Eu（Ⅲ）in present/absent humic acid were investigated.In general,fulvic acid could promote the adsorption of Eu（Ⅲ）on nano-composites,and the extent of promotion was obviously related to the pH values.The presence of fulvic acid could be promoted the adsorption performance of Eu（Ⅲ）at low pH values,whereas,the influence of Eu（Ⅲ）on functionalized GO composites was limited at higher pH values.The adsorption propotion still remained above 50%after 7 times of adsorption-desorption,which could be recycled for many times.In this paper,the adsorption capacities of functionalized Ca-Mg-Al LDH/GO and CM-β-CD/GO were tested by macroscopical bath experiments.The adsorption mechanism of Eu（Ⅲ）onto functionalized GO composites were further clarified in the presence of FA.The research results have especial reference values and practical guiding significances for nano-composites with highly efficient enrichment and elimination of environmental pollutants.