Study On The Adsorption Behavior Of Uranyl By Functionalized Metal-organic Frameworks

With the rapidly development of economy,the exploitation and utilization of nuclear energy have attracted extensive attention of most countries.However,in the process of developing nuclear energy,a large amount of low concentration of uranium wastewater are produced,uranyl ions are highly liquidity and extremely dissolve in water,can directly or indirectly access the food chain,with strong toxicity and radioactive,causing a threat to the human and the environment.Therefore,how to realize the purification of uranium-containing wastewater is a current research focus,which is of great significance to human health and environmental protection.Herein we report Mental-Organic Framework materials MIL-125 and NH₂-MIL-125 synthesized by solvothermal method.The materials have been characterized by using XRD,SEM.The adsorption performance of the adsorbents for UO₂²⁺were investigated at different initial p H,uranium concentration,and contact time.The results showed that MIL-125 and NH₂-MIL-125 exhibited the strongest adsorption capacity for UO₂²⁺when the initial p H was 5 and 8,respectively.Adsorption properties of the two materials showed that the adsorption processes were more consistent with the Langmuir equation.At 25℃,the maximum adsorption capacity of MIL-125 and NH₂-MIL-125 were 264.40 mg·g^-1and 327.30 mg·g^-1,and the optimal adsorption time were 480 min and 70 min.In this work,pure gadolinium oxide（Gd₂O₃）and mixed gadolinium oxide（Gd₂O₃）-magnesium oxide（Mg O）composites were synthesized by simple hydrothermal method and calcination treatment.Two kinds of materials were used to remove uranyl ions from aqueous solution and characterized the structure and morphology by means of XRD,FT-IR et al.Mg O was introduced into Gd₂O₃material,which effectively avoided the agglomeration of Gd₂O₃material and increased the adsorption capacity.At 25℃,the maximum adsorption capacities of Gd₂O₃and Gd₂O₃-Mg O for UO₂²⁺were 473.43 mg·g^-1and 812.41 mg·g^-1,respectively.The pseudo-second-order kinetic model and Langumir isotherm model were fitted well with adsorption process.The thermodynamic fitting parameters（ΔG<0,ΔS>0,andΔH>0）indicated that the adsorption properties are endothermic and spontaneous.Gd₂O₃-Mg O has stability and regeneration ability are reduced after three times of reuse.The possible adsorption mechanism mainly involves the complexation of-OH and U（Ⅵ）generated by the hydration on the surface of the materials.The zeolitic imidazole frameworks material NH₂-ZIF-7 was prepared in this paper,and dopamine was polymerized in situ on the surface of NH₂-ZIF-7 to form the functionalized NH₂-ZIF-7@PDA material.The structure and morphology of the two kinds of materials were characterized by BET XPS et al.The adsorption effect of the two kinds of materials on uranyl ions were investigated by static adsorption experiments.The results show that NH₂-ZIF-7 and NH₂-ZIF-7@PDA materials have the maximum adsorption capacity for uranyl ions at p H 5 and 6,respectively.The data showed that more fit with Langmuir isotherm model,the maximum adsorption capacity of NH₂-ZIF-7 and NH₂-ZIF-7@PDA were 706.25 mg·g^-1and 1028.66 mg·g^-1,respectively.Adsorption kinetics experiments show that NH₂-ZIF-7 reaches adsorption equilibrium at 200 min and NH₂-ZIF-7@PDA at 120 min.The adsorption capacity of NH₂-ZIF-7@PDA for uranyl ion was still as high as 513.33 mg·g^-1after three times of recycling.