Directional dendritic gels constructed by binder-regulated freeze casting for enhanced uranium extraction from seawater

Directional microchannels can speed up the transportation of seawater in adsorbents, and the introduction of nanopores in the microchannels can enhance the specific surface area and endow the adsorbent with more adsorption sites, which are beneficial for improving the uranium adsorption ability. Herein, directional dendritic and hierarchical porous aerogels (DDH-PAO gels) were constructed by the binder-regulated freeze casting. The gels displayed directional dendritic channels and special honeycomb-like nanopores, which endowed the DDH-PAO gels with a rapid water permeation rate (0.74 s) and a large BET area. They exhibited good uranium adsorption capacities of 494.34 mg-U/g-Ads (in 16 ppm U-spiked simulated seawater) and 6.3 mg-U/g-Ads (in nonspiked natural seawater). The adsorption process can be observed by the naked eyes due to significant color changes before and after uranium adsorption. The uranium adsorption mechanism was analyzed by kinetic models and XPS spectra, and the role of regulators in microstructures formation was investigated by changing the amount of PVA. The directional microchannels, honeycomb-like nanopores, rapid water transportation rate, and high mechanical strength indicated that the DDH-PAO gels are promising for real uranium extraction from seawater.