Morphology Controlled Covalent Organic Framework Nano-Trap for Synergetic Uranium Adsorption and Photoreduction

Abstract

Covalent organic frameworks (COFs) without donor–acceptor pairs or inefficient separation of photogenerated electrons are usually considered unfavorable for photocatalysis due to electron-hole recombination. However, the study demonstrates a nitrile (CN) functionalized covalent organic framework nano-traps (COF-nTs; COF-nTS₁, COF-nTS₂, and COF-nTS₃), in which the CN groups act as electron-withdrawing centers, surrounding electron and facilitating charge separation, transport, and adsorption process. To further enhance the efficiency of charge carriers, a special approach is introduced to integrate morphology control through acid regulation and defect engineering. These key strategies optimize the key structure and improve photocatalytic performance, achieving a maximum uranium extraction capacity of 3548.1 mg g⁻¹, which is significantly higher than previously reported COF-based photocatalysts under visible light. A flexible 3 × 6 cm film of COF-nTs₃ is prepared by the blade coating method, successfully extracting uranium from spiked seawater with a 7-day capacity of 76 mg g⁻¹, a saturation capacity of 193 mg g⁻¹, and 0.2 day half saturation time. This demonstrates its potential for uranium extraction from aqueous solutions.