| Uranium（U）is not only an indispensable resource of nuclear fuel,but also a dangerous radionuclide with chemical toxicity or radioactivity.With uranium mining and industrial production,including nuclear fuel cycle,uranium conversion,fuel manufacturing,use of phosphate fertilizer and other industrial applications,a large number of uranium-containing wastes will be generated.As more and more radioactive uranium（Ⅵ）is released into the surrounding environment,there is a long-term potential hazard to soil,surface water and groundwater.Uranium（Ⅵ）and uranium（IV）are the two main forms of uranium.Uranium（Ⅵ）has higher solubility,mobility and toxicity.The negative effects of uranium（Ⅵ）on public health are more serious than that of uranium（IV）.A growing number of data indicate that excessive exposure to uranium can lead to fatal lesions and genetic mutations in organisms.It causes longterm toxicity and cancer.Therefore,the treatment of radioactive waste has become the focus of attention all over the world.For the recovery of uranium resources and the security of ecosystem,it is of great significance to remove and separate uranium（Ⅵ）from aqueous solution.Since uranyl ions can coordinate with uranyl ions and effectively bind metal ions,many studies have proposed that uranyl ions have a broad prospect as a material to capture heavy metal ions and uranyl ions.In this paper,Cucurbit[6]uril（CB[6]）has been firstly prepared according to previous studies,and a variety of CB[6] based composites were prepared by combining CB[6] with other materials by solvothermal method,impregnation method and other methods,which were used for the adsorption of uranium ions in aqueous solution.Objective:By comparing the adsorption performance of raw materials and composite materials for radionuclide uranium,it is investigated whether the adsorption performance of original single material for uranium ion is improved by introducing CB[6].In the static adsorption system,the optimal p H was determined by controlling the variables.The adsorption kinetics of uranium ions on composite materials was studied.Langmuir and Freundlich isothermal adsorption models were used to simulate the adsorption data.It lays a theoretical foundation for further exploration of the adsorption of radionuclide uranium in the wastewater of cucurbituril and composite materials.Methods:Scanning electron microscope（SEM）and transmission electron microscope（TEM）were used to observe the morphology of the composites before and after.The crystal structure of the samples was measured by Cu-KA X-ray diffractometer（XRD,SAXRD）.The complexation between adsorbents was confirmed by Fourier transform infrared spectroscopy（FT-IR）.X-ray photoelectron spectroscopy（XPS）was used to detect the types of elements and chemical bonds in the composites.N2 adsorptiondesorption isotherms and BET were used to analyze the changes of specific surface area,pore size and pore volume of the composites.The thermal stability of the composite was tested by thermogravimetric analysis（TGA）.Trace uranium analyzer and ICP-OES were used to determine the concentration of uranium ions in the adsorption solution.Results:1.Cucurbit[6]uril（CB[6]）and mesoporous silica（SBA-15）were effectively combined by simple impregnation method to successfully prepare mesoporous composite SBA-15@CB[6].The adsorption of U（Ⅵ）on the composite reaches equilibrium about 20 min,the optimal adsorption p H is 4.5,and the maximum adsorption capacity is 200.8 mg/g.The adsorption behavior conforms to the quasisecond-order kinetic model and Freundlich isotherm model,and belongs to chemisorption.In addition,the repeated use of adsorption-desorption cycle of composite materials was also studied.In at least four adsorption-desorption cycles,the adsorption capacity of composite materials remained stable,the adsorption capacity was still about 70 mg/g,and the adsorption capacity did not decrease significantly.2.Cucurbit[6]uril（CB[6]）-macroporous carbon（MC）composites with different mass ratios were successfully synthesized by solvothermal method.The adsorption of uranium in wastewater was studied by using the composites.At p H=5,the composite with high CB[6] content shows excellent adsorption performance for uranium,and the maximum adsorption capacity of 25%CB[6]-MC can reach 343.6 mg/g,which is significantly higher than the adsorption capacity of activated carbon microspheres.The adsorption behavior accords with Langmiur adsorption model,and has good repeatability and stability.3.Using SBA-15@CB[6] as a template,a unique Cucurbit[6]uril derived nitrogendoped mesoporous carbon（CMK-3-CB[6]N）composite was successfully synthesized through sucrose carbonization reaction.At p H=5,CMK-3-CB[6]N composites show excellent adsorption performance for uranium,and the adsorption behavior conforms to Langmiur adsorption model.The simulated maximum adsorption capacity can reach197.3 mg/g,and the adsorption equilibrium can be reached in 40 minutes at room temperature,and the adsorption process tends to mimic second-order kinetic equation.Conclusion:1.Using SBA-15 as a carrier,a simple and feasible method was adopted to load CB[6] onto the surface of SBA-15,and a new mesoporous SBA-15@CB[6] composite was synthesized.At p H=4.5,298 K,the SBA-15@CB[6] composite has good adsorption effect and is an excellent composite adsorbent for uranium（Ⅵ）adsorption.2.A new type of activated carbon composite has been successfully synthesized by simple and efficient solvothermal method.25%CB[6]-MC composite with high CB[6]content has the maximum adsorption capacity of 343.64 mg/g of Uranium（Ⅵ）from water at p H=5 and 25℃.Compared with the activated carbon microspheres,the adsorption performance was significantly improved.3.Cucurbit[6]uril-nitrogen doped mesoporous carbon（CMK-3-CB[6]N）composites were prepared by doping CB[6].CMK-3-CB[6]N has good adsorption capacity for uranium（Ⅵ）,and its monolayer adsorption capacity is significantly higher than that of CMK-3 before modification.CMK-3-CB[6]N is considered to have broad prospects in the application of uranium（Ⅵ）removal in aqueous solution. |
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