Design And Synthesis Of Ionic Covalent Organic Frameworks And Their Adsorption Properties For Uranium And Rhenium

With the development of the nuclear energy industry,the efficient disposal and recovery of nuclear waste in the process of nuclear fuel cycle are of great ecological significance.⁹⁹Tc produced during the fission of ²³⁵U or ²³⁹Pu is a radioisotope with a long life.It usually exists in the form of Tc O₄^-anion with non-complexing properties and high water solubility.Efficient and selective removal of Tc O₄^-from wastewater remains a major scientific puzzle and technological challenge.Uranium,as an essential resource for nuclear energy production,is of strategic importance for the sustainable development of the global nuclear industry.With terrestrial uranium reserves dwindling,extracting uranium from seawater has aroused intense interest of researchers.However,recovering uranium from seawater is challenging due to its extremely low uranium concentration,ultra-high salinity and the presence of a large number of interfering ions.Ionic covalent organic frameworks（i COFs）are a new kind of crystalline organic polymers composed of ionic frameworks and corresponding counterions.Due to its adjustable structure,clear channels and abundant charged sites,i COFs have shown great potential in many application areas such as adsorption,separation,and sensing.This paper studies the adsorption of Re O₄^-（the non-radiative substitute of Tc O₄^-）and UO₂²⁺based on the design and synthesis of i COFs.The main research contents are as follows:1.3D viologen-based covalent organic framework for selective and efficient adsorption of Re O₄^-/Tc O₄^-.Due to the long half-life and high environmental mobility,the selective and efficient capture of Tc O₄^-from nuclear effluents is very important,but it is still very challenging.Herein,a novel three-dimensional（3D）cationic covalent organic framework（TFAM-BDNP）was designed and synthesized via Zincke reaction for efficient and selective capture of Re O₄^-/Tc O₄^-.TFAM-BDNP has an open 3D hydrophobic channels,abundant active sites and high chemical stability with high adsorption capacity and ultrafast exchange kinetics for Re O₄^-.TFAM-BDNP still shows good adsorption performance for Re O₄^-at p H 2-12 and in the presence of excess competing anions.Even in the simulated Hanford flow sample,TFAM-BDNP has outstanding removal efficiency of Re O₄^-.This study develops a novel adsorbent for efficient capture of Re O₄^-/Tc O₄^-in complex environments and provides an effective strategy for broadening the types of 3D COFs.2.Cationic covalent organic framework for selective detection and adsorption of Re O₄^-/Tc O₄^-.Tc O₄^-poses a serious threat to groundwater pollution and aquatic organisms due to its high water solubility and mobility.Therefore,it is of great importance to develop new materials for simultaneous detection and removal of Tc O₄^-.Re O₄^-is generally considered a non-radiative alternative to Tc O₄^-due to the similar chemical properties of Re O₄^-and Tc O₄^-.In this study,a new cationic COF（BTTA-BDNP）based on linked carbazole unit was synthesized via Zincke reaction.The high stability,regular pore size and strong fluorescence emissions of BTTA-BDNP make it a unique platform for fluorescence detection of Re O₄^-/Tc O₄^-.BTTA-BDNP has ultra-fast fluorescence response time and ultra-low detection limit（66.7 n M）for Re O₄^-.Meanwhile,due to the hydrophobic skeleton and high charge density,the adsorption capacity of BTTA-BDNP for Re O₄^-selective trapping is high and the adsorption kinetics is fast.This study not only develops efficient methods for monitoring and removing Re O₄^-/Tc O₄^-,but also provides strategies for the design and development of environmental remediation materials.3.Anionic covalent organic framework for extracting uranium from seawater.Uranium is the main resource for nuclear energy production,and extraction of uranium from seawater is of great strategic importance.However,its low concentration of uranium,the high salinity and the presence of a large number of interfering ions make extracting uranium from seawater a challenging task.In this work,the anionic COF（Bd-Th-SO₃Na）with charged groups was obtained by introducing sulfonate into the covalent organic framework.The abundance of charged groups in ion channels of Bd-Th-SO₃Na enables fast and controlled UO₂²⁺transport through electrostatic interactions.In addition,the sulfonic acid unit can enhance the affinity for UO₂²⁺through coordination interactions,resulting in efficient selective adsorption of uranium.The experimental results show that Bd-Th-SO₃Na has up to1576 mg g^-1 uranium adsorption capacity,excellent selectivity,ultra-fast kinetics（5min）and good reusability.Even under complex environmental conditions,Bd-Th-SO₃Na has the high removal efficiency for uranium,showing a good application prospect.This study not only provides an efficient platform for extracting uranium from seawater,but also provides new ideas for the enrichment and recovery of other important resources.