In Situ Synthesis of Polyamidoxime Chains Inside the Negative‐Charged Confining Fields for Efficient Adsorption of Uranyl Ions

Abstract Polyamidoxime (PAO) and its derivatives are widely regarded as promising adsorbents for uranium extraction from seawater. However, their close‐packed structure encapsulates a large number of adsorption sites and slows down the transfer rate of uranyl ions, resulting in a slight uranium adsorption capacity. Herein, PAO polymer chains are synthesized through the molecular coordination template method in the carboxylate covalent organic framework (COF) to obtain a PAO‐inserted COF adsorbent with open ion transport channels. After removing the protons, the COO⁻ groups form in situ electric fields inside the 0.7 nm COF channel. This negatively‐charged framework reduces the electrostatic repulsion among uranium cations, thus realizing ultrahigh utilization of adsorption sites of PAO polymer (81.0%), far exceeding that of classical amidoxime‐based adsorbents (33.7%). After 10 days of contact with natural seawater, COF‐PAO achieved an average capacity of ≈12.26 mg‐U per g for uranium in Bohai (China), satisfying the uranium extraction standard (6.0 mg g⁻¹). This work enumerates a method for the control of the spatial environment of polymer chains, and provides guidance for the design of subsequent high‐efficiency adsorbents.