Modulating tris-acid integrated proton-confined motifs for efficient uranium extraction from natural seawater

Uranium predominantly exists as the anionic [UO₂(CO₃)₃]^4- complex in seawater; conventional uranium adsorbents cannot displace carbonate ligands from the uranyl core via competitive coordination, resulting in inherently low uranium extraction efficiency. Herein, we report a class of unprecedented porous adsorbents featuring tris-acid (triphosphonate/trisulfonate/tricarboxylate) integrated proton-confined motifs. In contrast to traditional sorbents, the incorporated tris-acid moieties suppress proton release through extensive hydrogen-bonding networks, enabling the formation of protonated uranyl tricarbonate species upon contact with [UO₂(CO₃)₃]^4-. Such a localized proton microenvironment lowers the energy barrier for CO₃^2- dissociation from [UO₂(CO₃)₃]^4-, and the liberated uranyl ions are rapidly re-coordinated by the tris-acid integrated anionic binding sites. Among the synthesized materials, the tricarboxylate-based MIPAF-17 exhibits the highest affinity toward uranyl carbonate, achieving an exceptional distribution coefficient (K_d) of 1.3 × 10⁸ mL g^-1. Moreover, it delivers a remarkable uranium uptake capacity of 19.0 mg g^-1 within 15 days in natural seawater. This work establishes a general design paradigm for high-performance adsorbents toward uranium extraction from seawater.