Design And Synthesis Of Olefin-linked Covalent Organic Framework For The Selective Extraction Of Radioactive Elements

Nuclear energy is an ideal clean energy compared to traditional fossil fuels.Uranium is the main fuel for nuclear reactions,and its efficient extraction has received widespread attention from researchers.With about 4.5 billion tons of uranium contained in the oceans,and its reserves is nearly 1000 times that on land.So capturing the radioactive elements uranium from marine is one of the most promising ways to address the current shortage of uranium resources.With the development of nuclear energy,large amounts of radioactive elements were inevitably released into the environment.Technetium(⁹⁹Tc)having a long half-life and strong radioactivity,usually present in the form of ⁹⁹Tc O₄^-,which is one of the most dangerous radioactive elements in the environment.Removing ⁹⁹Tc O₄^-from wastewater is important for environmental protection.At present,many methods have been developed to capture radioactive elements uranium and technetium from water,among which adsorption method has the advantages of strong adaptability and environmental friendliness.However,in complex practical environments,the efficient selectively capturing of uranium and technetium remains a tough task.Therefore,the development of new,efficient and stable adsorbents for the selective enrichment of uranium and technetium is of great significance.Covalent organic frameworks（COFs）are a new class of lightweight crystalline porous materials,its designability and high specific surface area make it a potential material for capturing radioactive elements.Among the many connection modes of COFs,olefin linked COFs have received widespread attention for their excellent stability and good photovoltaic performance.Based on the structural and functional characteristics of olefin linked COFs,functional units with specific affinity to uranium and technetium this paper designs.A variety of COFs materials with innovative structure are synthesized for efficient capture of radioactive elements in environmental media,which is expected to strategic resource enrichment and environmental governance.The main research content is as follows:1.Olefin linked cationic 3D COF for capturing Re O₄^-.Compared to 2D COFs,3D COFs typically have a higher surface area and more easily accessible active locations,making 3D COFs with good application prospects in the field of absorption and separation.In this paper,olefin-linked cationic porous 3D COF（TAPM-PZI）was prepared by Aldol condensation reaction and used to selectively capture Re O₄^-.TAPM-PZI shows high crystallization,regular porosity,chemical stability and ionic properties,with an absorption capacity of 542.3 mg g^-1 and ultra-fast ion exchange dynamics（30 s）for Re O₄^-（a non-radioactive substitute for Tc O₄^-）.Even under conditions of the p H range of 2-10 and the presence of excessively competitive anions.TAPM-PZI still exhibited good removal performance for Re O₄^-and removal efficiency of Re O₄^-up to 86.4%in simulated Hanford LAW.This study not only developed a new type of adsorbent that can effectively capture Re O₄^-/Tc O₄^-in complex environments,but also expanded the application of 3D COFs in the environmental field.2.Photoinduced enhanced extraction of uranium from seawater using olefin linked covalent organic framework.When extracting uranium from seawater,biological fouling is the main reason that prevents the efficient extraction of uranium by adsorbents.In this paper,COFfunctionalized with amidoxime（BD-TN-AO）was synthesized by Knoevenagel condensation reaction.The extendedπ-conjugation system provided by the highly conjugation diethylene（-C≡C-C≡C-）units and the-C=C-bond in BD-TN-AO endows BD-TN-AO with good photocatalytic activity.Therefore,BD-TN-AO can produce bio-toxic active oxygen and photogenic electrons under illumination,giving it a high anti-biofouling activity and reducing the adsorbed U（VI）to insoluble U（IV）.Meanwhile,the surface of the BD-TN-AO produces a large amount of electrostatic photogenic holes,which can electrostatic attract[UO₂（CO₃）₃]^4-in seawater,significantly improving the extraction capacity of uranium.Due to the excellent light-induced effect,BD-TN-AO has an absorption capacity of up to 5.9 mg g^-1 of uranium in microbial natural seawater.This study suggests that the design of olefin linked COF materials will be an effective strategy for light-induced enhancement of seawater uranium extraction.3.3D olefin linked covalent organic frameworks are used for efficient electrical extraction of uranium.Extracting uranium from marine water provides an opportunity for sustainable nuclear fuel supply,but the extremely low concentration of uranium（～3ppb）in seawater makes this task extremely challenging.In this paper,3D COF functionalized with amidoxime（TFPM-PDAN-AO）was prepared,which has regular three-dimensional channels,excellent stability and photoelectric properties,and can be used as a porous platform for the electrical extraction of uranium.By applying alternating voltages between-5 and 0 V,uranyl ions(UO₂²⁺)can rapidly migrate and enrich into the porous structure of TFPM-PDAN-AO,then inducing the electrodeposition of uranium compounds to form the charge neutral species(Na₂O（UO₃H₂O）_x with an unprecedentedly high adsorption capacity of 4,685 mg g^-1.This work not only provides technical support for extracting uranium from electrodeposited seawater,but also expands the application prospects of functional 3D COFs.4.r GO-based covalent organic framework hydrogel for photothermal desalination and uranium capture.Due to the relative hydrophobicity of amidoxime functionalized COFs,UO₂²⁺is difficult to diffuse into the porous channels of COFs.Moreover,the COFs used in the extraction of uranium from seawater are usually in powder,and their recyclability is a significant challenge.In this paper,a kind of r GO@covalent organic skeleton hydrogel（KTG）was prepared as a porous platform for synergistic photothermal desalination and uranium extraction from seawater.Under simulated sunlight,the floating KTG achieves thermal localization on the surface,and a large amount of water can be transported to the KTG surface through 3D porous hydrophilic channels,thereby continuously generating solar steam.Meanwhile,the increase of KTG surface temperature can promote the rapid diffusion of uranyl ions in the hydrogel 3D network,significantly improving the adsorption efficiency and capacity of uranium.In addition,KTG’s excellent photocatalytic activity and mechanical properties make it have highly resistant to biological fouling and good reusability,enabling continuous uranium capture and solar distillation.The strategy developed in this work is also applicable to the recovery of other strategic resources,and is expected to promote the commercial use of COFs materials.5.Biological ion transport system has served as a natural prototype for designing artificial channels.Due to the presence of specialized ion channels,it can provide high selectivity and high transmission performance.However,developing stable and selective artificial ion channels remains a formidable challenge.Inspired by the principle of charge interaction and the biological ion channel,the sodium4-styrenesulfonate（PS）/4-vinylbenzoic acid（VBA）was encapsulated into amidoxime functionalized COFs（COF-AO）channels in situ,and a COF-AO-Poly with built-in electric field was constructed.The synergistic effect between the densely populated uranium sites and anion chains in COF-AO-Poly skeleton significantly improves the adsorption capacity of uranium,and its adsorption capacity is 3.8 times that of COF-AO.Meanwhile,the anion channel confined in the COF channel provides a transport medium for UO₂²⁺,while other ions are blocked,thus achieving high selectivity and high adsorption rate.This work developments a brand-new COF adsorbent,and opens up a new way for design of multifunctional materials for simulating biological systems.