Design And Synthesis Of Metal Organic Framework Materials For Adsorption Of Uranium/Iodine

Nuclear energy is considered an efficient and clean energy source that supplies13%of the world’s electricity.Large quantities of radioactive wastewater containing uranium have been inevitably released into the environment with the rapid development and wide application of global nuclear energy since uranium is the current major fuel in most commercial reactors.At the same time,the main source of radioactive iodine is the fission process of the nuclear fuel uranium(²³⁵U)in nuclear reactors.These two elements with high chemical and radioactive toxicity will not only pose a great threat to aquatic organisms and the environment,but also may indirectly through the food chain enter the human body,causing the damage to people’s health greatly.At present,there are many methods for extracting radionuclides,among them,adsorption has been the most popular method because of its simplicity,high efficiency,and economy.Currently reported adsorbents such as inorganic materials,polymers,carbon-based materials and magnetic materials are often limited by their stability,adsorption capacity,adsorption kinetics,selectivity,or reusability.Metal-organic frameworks（MOFs）are crystal materials formed by metal ions and organic linkers connected by coordination bonds.They have regular structure,rich topological types,high stability and adjustable function.A variety of new MOFs were designed in this paper to achieve efficient enrichment of uranium and iodine in environmental media.The main research contents are as follows:1.Extracting low concentration uranium from water presents a great challenge to traditional capture materials.A facile one-pot strategy was presented to obtain a novel metal organic framework（denoted as Mn-NDISA）for stable and efficient trapping of low concentration uranium.Mn-NDISA with a built-in hydrophobic cavity can boost the adsorption affinity through the cooperative capture composed of electrostatic interaction,coordination force and hydrogen binding.Owing to the coordination-available oxygen sites in flexible framework,a rapid kinetic equilibrium was achieved in just 25 min.Moreover,these exceptional adsorption features enabled Mn-NDISA to successfully capture the uranium traces（～ppb）in wastewater samples.The experimental and theoretical studies revealed that the electrostatic attraction came from the surface negatively charged Mn-NDISA and the positively charged UO₂²⁺.The coordination originated from the strong affinity between oxygen-containing functional groups and UO₂²⁺,while hydrogen bonds further reinforced the as-formed uranium binding complex.This research offered a promising cooperative capture strategy to improve the uranium affinity of MOFs for trace contaminants removal in environmental remediation fields.2.Separating and recovering uranium from the real-world water environments remains a problem.A novel MOF（Mn-dcphOH-NDI）was synthesized for UO₂²⁺adsorption from wastewater and seawater.Mn-dcphOH-NDI exhibits high uranium adsorption capacity and rapid adsorption kinetics（20 min）because of electrostatic interaction and the abundant hydroxyl and carbonyl groups in the ordered channel.Mn-dcphOH-NDI shows excellent selectivity for uranium in the high concentration of competitive ions,because the distance of oxygen-containing sites in the acute angle corner of channel matches with the diameter of uranyl hydrate to improve the binding force.In addition,Mn-dcphOH-NDI successfully adsorbs uranyl ions from complex environmental water.This work provides a new material for obtaining MOFs based uranyl adsorbents that can be used under various water systems.3.By mimicking the binding motifs of bioreceptors,uranium adsorbent has been developed to meet this criterion:positioning direct chelation sites and hydrogen-bonding sites inside deep hydrophobic cavity of MOF.Benefiting from well-designed specific microenvironment namely the regular spatial structure and an unusual synergy from hydroxyl and carbonyl groups,MOF shows enhanced comprehensive adsorption performance.The MOF CaNDI-oOH shows outstanding performance towards uranium enrichment with chemical and radiation stability,exceptional uptake capacity,fast kinetics,high anti-interference ability,excellent reusability.And,this adsorbent is able to almost completely remove uranium from environmental water samples within 30 min,highlighting the potential application in radionuclide removal from wastewater.The experiment results and DFT calculation suggest biomimetic multiple interactions are responsible for high performance uranium capture.The cooperative interactions strategy established here reveals a new paradigm in enhanced uranium extraction for MOFs.4.The effective capture of radioactive iodine is of importance for nuclear waste disposal,and the design and preparation of simple and efficient iodine adsorbents is still difficult.An imidazolium-based cationic metal organic framework（Zntib）was synthesized with remarkable chemical stability and excellent crystallinity,which successfully realized the efficient capture of radioactive iodine.Zntib shows high iodine vapor adsorption capacity(2.31 g g^-1)at 75°C,exceeding the performances of most previously reported adsorbents.The regular structure of Zntib promotes rapid mass transfer of iodine,and it takes only 10 minutes to reach kinetic equilibrium in iodine solution.The high adsorption capacity of Zntib for iodine species in water(1435 mg g^-1)is due to the high density imidazole and phenyl groups and electrostatic interaction.In addition,the compound Zntib shows high selectivity and affinity toward iodine in the presence of coexisting competitive ions.These excellent adsorption properties have enabled Zntib to successfully remove iodine from mining wastewater with a removal rate of 96%.Thus,the ionic framework featuring electron-rich moieties provides a simple and efficient strategy for iodine capture.