Hydrophilic Molecular Chain Modified Polyacrylonitrile Fibers And The Uranium Adsorption Performance

Nuclear energy is considered to be one of the most promising energy sources for mankind in the future.However,uranium reserves on earth are few and unevenly distributed.Our country’s currently proven uranium reserves can only hold out for the next 70 years.Approximately 4.5 billion tons of uranium is in the sea,and the exploitation of marine uranium resources is of great significance to the stable and long-term stability of our country’s nuclear power industry.At present,the adsorption method is considered to be the most feasible technical solution in the field of uranium extraction from seawater due to its economical environmental protection and simple operation.Therefore,the development of efficient seawater uranium adsorbents has become the main goal of current scientific researchers.In this paper,polyacrylonitrile fiber（PAN）,a widely used material in the study of uranium extraction from seawater,was utilized as the matrix,and a hydrophilic monomer or polymer was utilized to graft a layer of molecular chains with swelling properties on the surface of the fiber.The hydrophilic groups contained molecular chains swell due to the penetration of water molecules.The uranium（U（Ⅵ））in water penetrates into the swelling layer as the water penetrates.The adsorption performance of the material is effectively improved due to the extraction between U（Ⅵ）and the adsorbent groups in the swelling layer.The swelling performance of amidoximized polyacrylonitrile fiber is improved by introducing strong hydrophilic amino groups,resulting in a swelling rate of 20.73%.The surface of PAN-NH₂-AO became hydrophilic with water absorption capacity of 20 g·g^-1.Meanwhile,the amino groups effectively prevent the excessive amidoximation reaction,leading to inhibited shrinkage of PAN fibers.PAN-NH₂-AO reaches a saturated adsorption capacity of 226.62 mg·g^-1 in a U（Ⅵ）solution at p H 5 within 180 minutes.The study of adsorption thermodynamics and kinetics of PAN-NH₂-AO shows that the adsorption process is a spontaneous homogeneous chemical adsorption.During the U（Ⅵ）adsorption process,PAN-NH₂-AO fibers swell due to the adsorption of large amount of water by the hydrophilic amino and amidoxime groups on its surface.U（Ⅵ）penetrates into the swelling layer with water and coordinates with amino and amidoxime groups on the molecular chain inside the swelling layer,which improves its adsorption performance.Through a two-step microwave reaction method,molecular chains with a large number of hydrophilic hydroxyl and phosphate groups were grafted onto the main chain of PAN surface.Due to the hydrophilic effect of the hydroxyl groups and amino trimethylene phosphonic acid（ATMP）in molecular chains,a large amount of water is absorbed,which causes the molecular chain to swell in water and formes a swelling layer on the surface of PAN.The hydrophilic properties of PAN-（OH）_n-P is effectively improved with water absorption capacity of 23 g·g^-1.PAN-（OH）_n-P reaches a saturated adsorption capacity of 234.74 mg·g^-1 at p H 7.The study of adsorption kinetics and thermodynamics show that the adsorption process of PAN-（OH）_n-P to U（Ⅵ）is a spontaneous homogeneous chemical adsorption.In the U（Ⅵ）adsorption process by PAN-（OH）_nP,the molecular chains in the swelling layer swell due to the hydroxyl and phosphate groups.U（Ⅵ）penetrates into the swelling layer with water molecules and coordinates with hydroxyl and phosphoric acid groups,thereby improving the adsorption efficiency.A hydrophilic swelling layer on the surface of electrospinning PAN nano non-woven fabric was constructed by the graft of hydrophilic amino containing polyethyleneimine.The hydrophilic property of fiber is significantly improved by amino and sulfonic acid groups.In water contact angle test,the surface of PAN fiber bulges and the water absorption capacity reaches 29 g·g^-1.The adsorption capacity of PAN-PEI-SA at p H 5 is 215.25 mg·g^-1.The study of adsorption kinetics and thermodynamics found that the adsorption process of PAN-PEI-SA to U（Ⅵ）is spontaneous and a uniform chemical adsorption.During U（Ⅵ）adsorption by PAN-PEI-SA,the molecular chains in the swelling layer swell because of the hydrophilic amino and sulfonic acid groups in the swelling layer.U（Ⅵ）penetrates into the swelling layer with water and coordinates with hydroxyl and sulfonic acid groups.The hyperbranched PAMAM molecular chains were branched on the surface of the PAN fiber by a multi-step method.Fiber swelling experiments show that the hyperbranched hydrophilic swelling layer constructed on the surface of PAN effectively improves the hydrophilic properties of PAN fibers,and find that the water absorption capacity and swelling rate are directly proportional to the hyperbranched generations.PAN-3G-PAMAM reaches the maximum adsorption capacity of 555.55 mg·g^-1 within 12 h at p H 5,and the adsorption capacity is also directly proportional to the number of hyperbranched generations.The result of adsorption kinetics and thermodynamics shows that the adsorption process of PAN-3G-PAMAM to U（Ⅵ）is a spontaneous chemical adsorption.The molecular chains in the hyperbranched swelling layer swell due to its hydrophilicity and the absorption of a large amount of water.And the main chain of PAN fiber swells simultaneously.U（Ⅵ）penetrates into the swelling layer with water and coordinates with amino and amide groups in the swelling layer.