Visualizing dynamic competitive adsorption processes between iodine and methyl iodide within single covalent organic...

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Covalent organic frameworks (COFs) are crucial porous materials for adsorbing volatile iodine (I₂) and methyl iodide (CH₃I).
• Understanding the dynamic adsorption mechanisms at the single-crystal level is essential for enhancing COF performance in gas capture and separation.

Purpose of the Study:

• To visualize and analyze the real-time, dynamic adsorption behavior of single COF crystals exposed to a binary gaseous mixture of I₂ and CH₃I.
• To elucidate the underlying reaction mechanisms and identify factors influencing the competitive adsorption processes.

Main Methods:

• Operando real-time dark-field optical microscopy (DFM) imaging was employed to monitor single LZU-111 COF crystals.
• Time-lapse imaging analyzed changes in red (R) and blue (B) intensities within DFM images to track gas uptake.
• Theoretical calculations were integrated to complement experimental observations.

Main Results:

• DFM imaging revealed that I₂ and CH₃I uptake caused distinct changes in R and B intensities.
• An unusual blinking phenomenon in R/B intensities was observed, indicating intermittent sorption-desorption cycles.
• The competitive adsorption between CH₃I and I₂ was shown to follow a multi-time, oscillatory pathway, not a simple successive one.

Conclusions:

• The study visualizes the dynamic, intermittent, and oscillatory nature of competitive I₂ and CH₃I adsorption in LZU-111 COFs.
• Intermittent blinking events are linked to CH₃I and I₂ sorption-desorption dynamics within the COF framework.
• Differences in migration capability and initial pressure were identified as key factors initiating these blinking events.