Design And Fabrication Of Easily Recycled Amidoxime Functionalized Chitosan Materials For Uranium Extraction From Seawater

Nuclear energy is a renewable low-carbon energy with high power generation efficiency.It is a strategic solution to cope with the increasingly severe energy shortage crisis and achieve the environmental development goal of green water and green mountains.Uranium is a key resource for the development of the nuclear energy industry.However,the uranium reserves on land are limited,and the total amount of uranium in seawater can reach about 4.5 billion tons.The effective capture of uranium in seawater is an important strategy to ensure the sustainable production of uranium resources in China.The design and development of high-performance adsorbent materials is a hot research topic in the field of uranium extraction from seawater.Amidoxime functionalized materials are uranium extraction materials with great commercial application prospects.Nevertheless,the reported advanced amidoxime materials have defects such as recovery and separation difficulties,limited adsorption rate and low uranium extraction selectivity,which greatly limit their practical application.Hence,it is highly important to design and develop amidoxime functionalized adsorption materials with easy separation feature and optimized adsorption kinetics and selectivity.Based on the above considerations,the main research contents of this paper are as follows:(1)Design and fabrication of porous chitosan-poly imide dioxime(Cs-PIDO)semi-interpenetrating network gel for uranium extraction from seawater.Using sodium bicarbonate as a pore-forming agent and chitosan and poly imide dioxime as precursors,Cs-PIDO hydrogels with semi-interpenetrating network structure were constructed.The material characterization showed that it had three dimensional porous structure and excellent hydrophilicity.By adjusting the relative proportion of components,the network structure and functionality of the material can be controlled.The uranium extraction from seawater by Cs-PIDO hydrogels with different proportions was studied systematically.The Cs-PIDO-1 hydrogel exhibit the best uranium adsorption performance thanks to the hierarchical pore structure and abundant uranium-binding groups.In uranium spiked aqueous solution,Cs-PIDO-1 hydrogel showed rapid kinetics,high adsorption capacity and good regeneration ability.Under real seawater conditions,the adsorption rate of Cs-PIDO-1 hydrogel reached 0.35 mg/g·d in the first 2 weeks,ranking among the best reported self-supporting amidoxime based materials.Its 4-week adsorption capacity reached 5.75 mg/g.Cs-PIDO hydrogel is a promising adsorbent for uranium extraction from seawater because of its high efficiency and rapid uranium extraction and its advantages of easy separation and regeneration.(2)Design and fabrication of poly(amidoxime)-magnetic chitosan(P(AO)-g-MC)for uranium extraction from seawater.P(AO)-g-MC was synthetized by grafting copolymerization of acrylonitrile on magnetic chitosan firstly,followed by amidoximation reaction of the nitrile groups.The embedded Fe3O4 nanoparticles made the composite superparamagnetic.Under the magnetic field,P(AO)-g-MC can be separated from the solution within 10 s.Uranium extraction performance of P(AO)-g-MC was systematically studied.Owing to the high density amidoxime functional group with strong affinity for uranium,P(AO)-g-MC showed a remarkable adsorption capacity,rapid kinetics and good regeneration performance in uranium spiked aqueous solution.Notably,the 7-day uranium adsorption capacity of P(AO)-g-MC from natural seawater in column mode was up to 5.14 mg/g,12 times that of vanadium.The excellent uranium uptake performance over vanadium originated from the strong coordination interaction between N and O in amidoxime groups and uranyl according to theoretical simulation.The advantages of rapid recovery and high selectivity make P(AO)-g-MC a very potential uranium adsorbent in natural seawater.