Adsorption Of U??? In Water By UiO-66-NH₂ And Its Modified Materials

The large amount of uranium-containing wastewater generated during uranium mining and smelting and uranium utilization has severely affected the ecosystem and public health.How to effectively remove U?VI?in wastewater has become an important subject in the field of sewage treatment.At present,the adsorption method is considered as one of the best methods to remove U?VI?due to its high efficiency,simple operation,and low secondary pollution.Metal-organic frameworks--UiO-66-NH₂ is very suitable as a new adsorbent for removing U?VI?in water due to its high stability,large specific surface area and easy function.In this paper,UiO-66-NH₂ and its polyethyleneimine?PEI?modified materials were prepared by solvothermal method and wet impregnation method,respectively,and for the study of U???adsorption in aqueous solution.The morphology and structure of the adsorbents were characterized by SEM,XRD,FTIR,XPS,etc.The effects of pH,dosage,adsorption time and other factors on the adsorption effect were investigated,and the adsorption mechanism was discussed.The obtained research results are as follows:?1?UiO-66-NH₂ with high adsorption capacity for U???was synthesized by solvothermal method under the condition of adding acetic acid.The experimental results show that when the temperature is 30??the dosage is 100 mg/L and the initial U?VI?concentration is 10 mg/L at pH=6,the removal efficiency of UiO-66-NH₂ for U?VI?is 97.17%,and the adsorption equilibrium is basically reached at 60 min.The adsorption process is spontaneous and endothermic,conforming to the quasi-second-order kinetics and Langmuir isotherm model,with a maximum adsorption capacity of 384.6 mg/g.The adsorption-desorption experiments show that UiO-66-NH₂ has a good repeatable property.The FT-IR and XPS data demonstrated that the amino groups,Zr-OH and Zr-O-Zr bonds play important roles in the U?VI?adsorption process.The adsorption mechanisms mainly involve the coordination between U?VI?and Zr-OH and C-NH₂,and also most likely involve the covalent binding of U?VI?to the bridged O atoms in the Zr-O-Zr structure.?2?PEI modified UiO-66-NH₂ was prepared by the wet impregnation method successfully.The crystal structure of the UiO-66-NH₂ skeleton will not be destroyed by the PEI load,but its XRD characteristic peak intensity will gradually weaken due to the increase of the mass of PEI,and too high PEI loading will cause the agglomeration of UiO-66-NH₂ grains becomes severe.The results of adsorption experiments show that the optimal mass ratio of PEI to UiO-66-NH₂ is30%,and when the initial U???mass concentration is 10 mg/L,the temperature is 30?,and the dosage is 80 mg/L,the adsorption efficiency of UiO-66-NH₂/PEI for U???is 98.2%at pH=6,and the adsorption reaction reaches adsorption equilibrium within 60 min.Adsorption kinetics and isotherm analysis show that the adsorption process complies with quasi-second-order kinetics and Langmuir model,and the maximum adsorption capacity reaches 452.49 mg/g.