Engineering biaxial stretching polyethylene membrane with poly(amidoxime)-nanoparticle and mesopores architecture for uranium extraction from seawater

Abstract

Conventional polymeric adsorbents encapsulate most of their ligand groups (such as amidoxime, AO) in dense structures, leading to problems such as low adsorption capacity for Uranium extraction from seawater (UES). The uranium coordination environment of polymeric adsorbents has not been positively identified even after decades of research. Therefore, a new and functional Biaxially stretched polyethylene (BSPE) membrane with Poly-amidoxime (PAO) nanoparticles, mesoporous architecture, and nano-channels (PAO-BSPE) was fabricated in this study for UES, based on the interfacial self-assembly of axial grafting chains. The underlying mechanism involved in the formation of the PAO-BSPE membrane was elucidated using first-principles computations of the various reactions. The engineered PAO-BSPE membrane exhibited excellent hydrophilicity, good mechanical properties, high specific surface area, and contained mesoporous architecture and nano-channels, which facilitated advantages in terms of kinetics, capacity, and renewability in both laboratory experiments and marine field-testing. After 64 days of adsorption in natural seawater, the PAO-BSPE membrane with a low degree of grafting of 70.5% exhibited a high uranium-adsorption-capacity of 12.67 mg-U/g-ads, which was 1.77 times higher than that toward vanadium. The PAO-BSPE membrane efficiently extracted uranium in the presence of high concentrations of co-existing ions, with the distribution coefficient reaching 4.09 × 106 mL/g in natural seawater. The total amount of uranium recovered by the PAO-BSPE membrane was 15.0 g in terms of yellow cake during a total submersion time of 30 days in the ocean. The adsorbent exhibited a long service life of at least 12 cycles. Furthermore, near-edge and extended X-ray absorption fine structure spectroscopy analyses suggested that the mechanism of uranium adsorption involved the formation of a stable complex via the linkage of uranium with two amidoximes in a cooperative chelating fashion. This study presents a new adsorbent with improved efficiency for UES, which has significant implications for the development of polymer adsorbents with high selectivity.