Highly amidoxime utilization ratio of porous poly(cyclic imide dioxime) nanofiber for effective uranium extraction from seawater

Fibrous adsorption material with amidoxime (AO) group is widely considered as the most prospect of industrial application in uranium (U) extraction from seawater. However, the challenge of the AO-based adsorbents is that the utilization of AO has encountered bottle-neck of less than 1/100, which is far from saturated for decades. Herein, we construct porous structure in raspberry-like nanofibers (NFs) with rearranged AO groups cyclic imide dioxime (CID) nanoparticles (CID NFs) to improve the AO utilization ratio during U adsorption. By adjusting the size of the CID nanoparticles in NF, the area of the functional groups can be maximum exposed, which resulted in a breakthrough of the AO utilization ratio with high adsorption capacity. In simulated seawater with a U concentration of 330 ppb, the highest AO utilization ratio can reach 1/31. After adsorption in natural seawater for 87 days, the adsorption capacity of U was determined to be 11.39 mg-U/g-ads with AO utilization ratio of 1/74. Furthermore, extended X-ray absorption fine structure (EXAFS) fits and nuclear magnetic resonance (NMR) spectra suggested that the mechanism of AO bind uranyl ion was a tridentate binding model with CID. Density functional theory (DFT) computational studies proved that the tridentate binding model was the most stable combination. Positron annihilation lifetime spectroscopy (PALS) found that the generation of smaller free-volume holes in CID NFs have a certain cooperative binding in space on U adsorption. The CID NFs with unique nano morphology, and special CID chemical structure provide a new idea and potentiality for a novel design of U adsorbents in future U extraction from seawater.