Imaging the Encapsulation of Formic Acids in Single LZU-111 COFs as Reductants, Microreactors, and Optical Microcavities for Record-High Iodate Anion Removal.

Covalent organic frameworks (COFs) represent attractive crystalline porous materials for the capture of radioactive iodate anions (IO). However, the optimization and improvement of COF performances have mainly relied on trial-and-error approaches using bulk ensemble samples, and high-performance COFs for IO treatment are still lacking. Here we image the encapsulation of formic acids in a model single LZU-111 COF (FA@LZU-111) to react with IO using dark-field optical microscopy (DFM) and quantitatively unveil the stepwise reduction kinetics of IO into I/I in real time. Sequential DFM analysis, supplementary characterization, and theoretical simulation reveal that FA@LZU-111 COFs serve as reductants, microreactors, and optical microcavities during IO reduction. Guided by mechanistic understanding, the bulk performance of FA@LZU-111 for IO was evaluated under visible light irradiation, showing a record-high removal capacity (2817.5 mg·g) and excellent selectivity. This study highlights how single-particle imaging reveals structure-activity relationships in a bottom-up approach and aids the rational design of high-performance COF materials.