Imaging the Encapsulation of Formic Acids in Single LZU-111 COFs as Reductants, Microreactors, and Optical...

Covalent organic frameworks (COFs) represent attractive crystalline porous materials for the capture of radioactive iodate anions (IO₃^-). 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 IO₃^- 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 IO₃^- using in situ dark-field optical microscopy (DFM) and quantitatively unveil the stepwise reduction kinetics of IO₃^- into I₂/I₃^- 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 IO₃^- reduction. Guided by mechanistic understanding, the bulk performance of FA@LZU-111 for IO₃^- was evaluated under visible light irradiation, showing a record-high removal capacity (2817.5 mg·g^-1) 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.