High-strength ionic hydrogel constructed by metal-free physical crosslinking strategy for enhanced uranium extraction from seawater

Uranium is one of the most important elements in the nuclear industry, and efficient extraction of uranium from the ocean is conducive to the sustainable development of nuclear energy. In this work, rigid perylene tetracarboxylate anion (PTC4- ) was introduced by physical (non-covalent) crosslinking strategy to obtain metal-free ionic hydrogel PAOIB-PTC. PTC4- not only increased the rigid structure content of ionic hydrogel, but also formed dynamic macrocycle AO-PTC with amidoxime (AO) through hydrogen bonds. Unlike reported heterogeneous additives, PTC4- did not undergo inhomogeneity or shedding. Therefore, PAOIB-PTC exhibited high strength (7.34 MPa), excellent solvent resistance and salinity tolerance. A large number of hydrophilic groups and multistage pore structure endowed PAOIB-PTC with high hydrophilicity, which facilitated U(VI) mass transfer and led to rapid adsorption rates (88.6 mg g-1 h-1, c0 = 250 ppm). Since the metal-free component enabled more adsorption sites to be utilized, the maximum adsorption capacity of PAOIB-PTC was as high as 1008.03 mg g-1, which exceeded most reported hydrogel-based uranium adsorbents. Experiments and DFT calculations proved that PAOIB-PTC possessed high adsorption selectivity through uranyl recognition via hydrogen bonding and synergistic coordination by supramolecular structure AO-PTC. The low-concentration uranium capture capability and excellent recycling performance demonstrated the practical application potential of PAOIB-PTC. This work provides an idea for the design of metal-free ionic hydrogels with high-strength, and the established PAOIB-PTC is expected to be a candidate material for enhanced uranium extraction from seawater.