Green Synthesis Of Citric Acid Cross-linked β-cyclodextrin Polymer And The Adsorption Of Uranium And Europium

With the development of nuclear energy,a large amount of radioactive waste,such as ²³⁵U,²³⁵Np,^152+154Eu,and ²³⁹Pu,have been discharged into aquatic systems.The increasing level of toxic radionuclides exhibits serious risks to human health,living resources,and ecological systems.It is necessary to remove radionuclides from aqueous solutions before the wastewater is discharged into the environment.Because of its low cost,easy operation and high adsorption efficiency,adsorption is considered to be the most promising treatment method.For ecological safety and human health,it is urgent to develop green,efficient and low-cost adsorbent materials.β-cyclodextrin is a natural,nontoxic and inexpensive cyclic oligosaccharide containing seven glucose units.Adsorbent based onβ-cyclodextrin（β-CD）has drawn wide attention owing to strong affinity,low costs and simple design.However,β-CD has high water solubility,limiting its application in environment protection.Water-insoluble cyclodextrin polymers（β-CDP）maintain the envelope recognition performance of cyclodextrin well,but also show good stability and chemical adjustability,so it has been studied by more and more researchers.Nevertheless,β-CDP are less used in nuclear wastewater treatment.The main research content of this paper is to prepare citric acid cross-linkedβ-cyclodextrin polymer（CA-β-CD）,which is applied to the adsorption of U（VI）ion and Eu（III）ion.The specific research methods and conclusions are as follows:1.The environment-friendly insoluble polymer（CA-β-CD）was prepared by a simple one-step esterification condensation reaction,and its structure was characterized by FT-IR,SEM,XRD and TG.The experimental results showed that the polymer was successfully synthesized and could be used in the next adsorption study.2.CA-β-CD was used as adsorbent in the adsorption of U（VI）ion.The CA-β-CD before and after adsorption of U（VI）ion were characterized by FT-IR and EDS.Then the effects of pH value,reaction time,initial U（VI）ion concentration and temperature on the adsorption were explored.The experimental results showed that when the pH value was 4.0,the reaction time was 60 min,the initial concentration of U（VI）ion was 60 mg/L,the temperature was 55℃,the maximum adsorption capacity of CA-β-CD to U（VI）ion could reach 150 mg/g.Moreover,the adsorption process accorded with the pseudo-second-order kinetic model,and the adsorption isotherm indicated that the adsorption process was more inclined to the Freundlich model;From the thermodynamic data,we can see that the adsorption process was spontaneous and endothermic.Using Mg²⁺,Zn²⁺,Co²⁺,Ni²⁺and Mn²⁺as coexisting ions,it was found that they had little effect on uranium adsorption process and the experiments of desorption and recycling showed that CA-β-CD had good regeneration.3.Besides U（VI）ion adsorption,it was also applied to the adsorption of Eu（III）ion.Similarly,the CA-β-CD before and after adsorption of Eu（III）ion were characterized by FT-IR and EDS.Then the effects of pH value,reaction time,initial Eu（III）ion concentration and temperature on the adsorption were explored.The experimental results showed that when the pH value was 5.0,the reaction time was 40 min,the initial Eu（III）ion concentration was 70 mg/L,the temperature was 55℃,the maximum adsorption capacity of CA-β-CD to Eu（III）ion could reach 152 mg/g.Moreover,the adsorption process accorded with the pseudo-second-order kinetic model and the adsorption isotherm indicated that the adsorption process was more inclined to the Freundlich model.From the thermodynamic data,we can see that the adsorption process was spontaneous and endothermic.According to the experiments of desorption and recycling,CA-β-CD had good regeneration.