Constructing Uranyl-Specific Nanofluidic Channels for Unipolar Ionic Transport to Realize Ultrafast Uranium Extraction.

High-speed capturing of uranyl (UO22+) ions from seawater elicits unprecedented interest for the sustainable development of the nuclear energy industry. However, the ultralow concentration (∼3.3 μg L-1) of uranium element leads to the slow ion diffusion inside the adsorbent particle, especially after the transfer paths are occupied by the coexisted interfering ions. Considering the geometric dimension of UO22+ ion (a maximum length of 6.04-6.84 Å), the interlayer spacing of graphene sheets was covalently pillared with phenyl-based units into twice the ionic length (13 Å) to obtain uranyl-specific nanofluidic channels. Applying a negative potential (-1.3 V), such a charge-governed region facilitates a unipolar ionic transport, where cations are greatly accelerated and co-ions are repelled. Notably, the resulting adsorbent gives the highest adsorption velocity among all reported materials. The adsorption capacity measured after 56 days of exposure in natural seawater is evaluated to be ∼16 mg g-1. This novel concept with rapid adsorption, high capacity, and facile operating process shows great promise to implement in real-world uranium extraction.