Hydrogel polyamidoxime shell layer constructed on cyclized polyacrylonitrile nanofibrous mats for efficient uranium extraction from seawater

Extracting uranium from seawater, which contains hundreds of times more than terrestrial ores, furnishes a sustainable energy resource while curbing carbon emissions. Nanofibrous-based amidoxime is the most reliable uranium adsorbent due to its abundant chelating sites and large surface area. However, the amidoximation (AO) of polyacrylonitrile nanofiber (PAN NFs) produces brittle and shrunk AO-PAN NFs, and the spinning of pre-amidoximed PAN produces sub-micro stiff poly amidoxime (PAO) NFs, restricting their applicability. Herein, pre-cyclization (210 °C) and optimized amidoximation are applied to construct a hydrogel shell layer from PAO on cyclized electrospun PAN NFs. Among different amidoximation ratios, AO10-CPAN mats (10 g/L) with a thin hydrogel PAO shell layer exhibit excellent mechanical strength, high uranium adsorption capacity reached 380 mg/g at pH 8, and maintained their structure and 89 % of their initial adsorption capacity after six adsorption-desorption cycles. Furthermore, a 20.6 mg/g uranium adsorption capacity is reached after 15 days of circulating spiked (300 ppb uranium) natural seawater through the AO10-CPAN mats, proving their excellent selectivity and the open-chain amidoxime is the main compound of PAO shell. The surface amidoximed cyclized PAN (AO10-CPAN) mats satisfy the mechanical and physiochemical requirements for effectively extracting uranium from seawater.