A Study on the Degree of Amidoximation of Polyacrylonitrile Fibers and Its Effect on Their Capacity to Adsorb Uranyl Ions

Abstract

Amidoximation of polyacrylonitrile (PAN) fibers was studied by reacting them with hydroxylamine. The chemical structure, mechanical intensity, and morphologies of PAN and amidoximated PAN (AO-PAN) fibers were evaluated by Fourier transform infrared spectroscopy, tensile tests, dynamic mechanical analysis, and scanning electron microscopy, respectively. A higher degree of amidoximation resulted in a higher conversion ratio (CR) of the nitrile group and a higher density of the amidoxime group, while also reducing the mechanical intensity of the fibers. During amidoximation, a hydrogel layer formed on the fiber surface by bonding with H2O molecules, increasing the diameter of the AO-PAN fibers. The layer thickness increased as the CR of the AO-PAN fibers’ nitrile group was increased. The hydrogel layer decreased the adsorption capability by hindering the diffusion of uranyl ions to the interior of the AO-PAN fibers. Therefore, a CR of about 10.8% would provide an appropriate balance between the mechanical properties and the adsorption capability.

An Ion‐Crosslinked Supramolecular Hydrogel for Ultrahigh and Fast Uranium Recovery from Seawater

“…However, due to the relative hydrophobicity of amidoxime‐functionalized polymers, they are typically dense in aqueous solutions, and the uranyl ions are difficult to transfer into the polymer interiors . Consequently, only the superficial amidoxime groups can attain high uranium adsorption efficiency . To improve the overall uranium adsorption capacity of the amidoxime groups, one effective strategy is to dramatically increase the specific surface area of these adsorbents (for instance, by designing microporous structures or ultrathin nanofibers).…”

Significantly Enhanced Uranium Extraction from Seawater with Mass Produced Fully Amidoximated Nanofiber Adsorbent

“…Amidoxime‐based polymers were identified as the most promising sequestering materials for uranium adsorption due to the relatively high affinity of amidoxime group toward uranyl ion (UO 2 2+ ) and facile preparation from amidoximation of nitrile‐containing polymers . Radiation‐induced graft polymerization (RIGP) and atom‐transfer radical polymerization (ATRP) strategies were commonly used to graft acrylonitrile monomer to some robust backbone polymer fibers, typically polyethylene (PE) fibers, to form polyacrylonitrile (PAN) grafted fabric, followed with the postamidoximation to convert nitrile groups to amidoxime groups . The best adsorption capacity of these fiber adsorbents reached around 225 mg‐U per g‐Adsorbents (Ads) in uranium spiked seawater and 6.9 mg‐U per g‐Ads after contact with natural seawater over an 8 week period in the field column test .…”

Leveraging Actinide Hydrolysis Chemistry for Targeted Th and U Separations using Amidoxime‐Functionalized Poly(HIPE)s

“…In contrast, investigation of the U binding environment in these systems produced models consistent with at least two amidoxime groups in the inner sphere suggesting materials with a higher AO loading would perform better. Recent work by Li and co‐workers found a direct relationship between UO 2 2+ uptake and AO functional group loading on polymer fibers up to a point where higher levels of AO loading actually resulted in worse U uptake performance. It is possible that the relatively low amidoxime loading in the poly(HIPE) materials discussed herein (compared with amidoxime‐functionalized polymer fibers used for uranium from seawater purposes) coupled with their large pore size, limits the ability of multiple amidoxime groups to bind U, thus preventing the formation of stable ( AO ) x −U−( AO ) y environments and explaining, at least in part, the Th/U selectively.…”