Real-Time Single-Particle Imaging of a Dynamic Host–Guest Interaction-Initiated Nanoconfinement Effect on Iodine Uptake

Fundamentally understanding the nanoconfinement effect within porous crystals is crucial for improving and extending their applications. Here, we report the real-time single-particle imaging of dynamic adaptive host–guest interaction between acetic acid (HAc) and covalent organic framework-300 (COF-300) to generate HAc-confined COF-300 (HAc@COF-300) under in situ reaction conditions, which initiates subsequent iodine uptake in an aqueous solution using a dark-field optical microscope (DFM). Operando DFM imaging reveals the adaptive deformation of COF-300 particles during the host–guest interaction process, which is attributed to the Lewis acid–base interaction-induced crystal contraction. Moreover, quantitative analysis shows that the HAc@COF-300 exhibits 65,000-fold higher binding affinity toward iodine than free HAc because of the increase in local concentration and close proximity under the nanoconfinement environment. With the guidance of the nanoconfinement effect, an adsorption reaction system consisting of HAc and COF-300 for capturing I2 is rationally designed and validated by macroscopic ensemble measurements, resulting in significantly improved adsorption performance by 7- to 8-fold. These findings highlight the nanoconfinement effects in adsorption/separation reactions.