Constructing an Amino-reinforced amidoxime swelling layer on a Polyacrylonitrile surface for enhanced uranium adsorption from seawater

Polyacrylonitrile (PAN)-based materials have been studied for decades as uranium (U(VI)) adsorbents, because the further products of abundant nitrile groups, amidoxime (AO) groups, show great affinity for U(VI) ions. However, excessive amidoximation could cause the shrinkage of PAN fibers, resulting in decreased adsorption performance. Hence, an amino-reinforced amidoxime (ARAO) swelling layer was constructed on the PAN fiber surface (PAN-NH2-AO) by modification of the strongly hydrophilic amino group to prevent shrinkage. The molecular chains in the ARAO swelling layer would be swelled due to the adsorption of a large amount of water. Simultaneously, U(Ⅵ) ions can penetrate into the ARAO swelling layer with water molecules and coordinate with amino or AO groups, leading to increased adsorption performance. PAN-NH2-AO exhibited maximum U(VI) and water adsorption capacities of 492.61 mg·g-1 and 20.32 g·g-1 at 25 ℃ with a swelling ratio of 20.73%, respectively. The adsorption capacity of PAN-NH2-AO was 0.312 mg·g-1 after a 91-day immersion in Yellow Sea, China. The study of the adsorption thermodynamics and kinetics of PAN-NH2-AO showed that the adsorption process was spontaneous homogeneous chemical adsorption. This paper proposes a novel method to obstruct amidoximation induced shrinkage and to maximize the potential application of PAN-based materials.