The Performance And Mechanism Of U(Ⅵ) Removal From Aqueous Solutions By A Metal-organic Framework(DUT-69)

The process of uranium mining and smelting will produce a large amount of low-co ncentration U（Ⅵ）-containing wastewater.Finding a treatment method with high efficiency,low-consumption,and reusability towards uranium-containing wastewater has become a high-profile research content.The adsorption has been researched by researchers from all over the world on account of low consumption,simple preparation and no secondary secondary pollution.DUT-69 is a new type of zirconium-based metal-organic frameworks（MOFs）based on metal zirconium and connected with thiophene ligands.Compared with ordinary MOFs,zirconium-based MOFs have better liquid phase stability,acid-base stability and thermal stability,and can graft or composite other materials to improve the performance of the framework.Permanent pores can be created in the remaining vacancies after solvent molecules are removed in the process of obtaining DUT-69,which helps increase the number of active sites and help the adsorbate diffuse.In this article,Zr-based MOF（DUT-69）was utilized for U（Ⅵ）removal in aqueous solutions,and the performance and mechanism of U（Ⅵ）removal are discussed.DUT-69 was fabricated by using zirconium tetrachloride and 2,5-thiophene dicarboxylic acid under the intervention of acetic acid via hydrothermal synthesis.SEM,EDS,BET,XRD and TGA were used to investigate the material morphology and structural properties of DUT-69,which proved that DUT-69 was successfully synthesized.The effect of experimental factors,i.e.,the initial dose of materials,p H value,reaction time,U（Ⅵ）initial concentration,reaction temperature were systematically investigated by batch adsorption experiments to explore the optimal adsorption conditions of DUT-69.The results showed that the optimal conditions:the initial dose is 0.15 g/L,the p H value is 6,the reaction time is 30 min,and the initial U（Ⅵ）concentration is 10 mg/L.The adsorption capacity of U（Ⅵ）can reach the highest.The adsorption rate of DUT-69 is 94%.As the indoor temperature rised,the adsorption capacity becomes higher and higher.The interfering ions,including Ca²⁺,Mg²⁺,Fe³⁺,NH₄⁺,CO₃^2-and SO₄^2-had no obvious effect on the adsorption of U（Ⅵ）on DUT-69,indicating that DUT-69 possessed an excellent selectivity.After 5 cycles of adsorption-desorption,the removal rate of the U（Ⅵ）uptake by DUT-69 was decreased from 94%to 80%,indicating that DUT-69 has good stability and can be used as one of the candidates for the treatment of uranium-containing wastewater.The adsorption data of U（Ⅵ）on DUT-69 was matching with the pseudo-second-order kinetic and Langmuir isotherm model.According to the formula calculation,the theoretical maximum total adsorption capacity of U（Ⅵ）can be as high as 362.32 mg/g.The fitting results of the intra-particle diffusion model show that the adsorption process was spontaneous.In the adsorption process,the boundary between the solid phase and the liquid phase will increase irregularly,and higher temperatures was conducive to the U（VI）adsorption on the surface of DUT-69.Characterizations such as FT-IR,Zeta potential,XPS,etc.show that the complexation interaction was main adsorption mechanism of U（Ⅵ）on DUT-69 and the electrostatic interaction was the secondary mechanism.The carboxyl,Zr-O,and C-S bonds played important roles in U（Ⅵ）adsorption.