Alkynyl-based sp2 carbon-conjugated covalent organic frameworks with enhanced uranium extraction from seawater by photoinduced multiple effects

Abstract

Biofouling is a major obstacle to the efficient extraction of uranium from seawater due to the numerous marine microorganisms in the ocean. Herein, we report a novel amidoxime (AO) crystalline covalent organic framework (BD-TN-AO) by Knoevenagel condensation reaction of 2,2',2'-(benzene-1,3,5- triyl)triacetonitrile (TN) and 4,4'-(buta-1,3-diyne- 1,4-diyl)dibenzaldehyde (BD) that is highly conjugated and possesses excellent photocatalytic activity. The excellent photocatalytic activity endows the BDTN- AO high anti-biofouling activity by producing biotoxic reactive oxygen species (ROS) and photogenerated electrons to efficiently reduce the loaded U(VI) to insoluble U(IV). Meanwhile, the surfacepositive electric field has strong electrostatic attraction to the negative [UO2(CO3)3]4- in seawater, which can significantly enhance the extraction capacity of uranium. Benefiting from these outstanding photoinduced effects of BD-TN-AO, the adsorbent exhibits a high uranium adsorption capacity of 5.9 mg g-1 under simulated sunlight irradiation in microorganism-containing natural seawater, which is 1.48 times the adsorption capacity in darkness.