Atomic Force Microscopy Strategies for Capturing Guest-Induced Structural Transitions in Single Flexible...

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Flexible metal-organic frameworks (MOFs) exhibit stepped adsorption isotherms, crucial for gas storage and separation.
• These steps arise from transitions between narrow-pore (np) and large-pore (lp) states, enabling high working capacities.
• Tuning transition pressure via particle size is key, but bulk measurements obscure size-dependent effects.

Purpose of the Study:

• To investigate guest-induced structural transitions in flexible MOFs at the single-particle level.
• To understand the size-dependent effects on MOF adsorption behavior.
• To analyze transition mechanisms and pressures using atomic force microscopy and thermodynamic analysis.

Main Methods:

• Utilized atomic force microscopy (AFM) to apply force to individual MOF particles.
• Analyzed force profiles to determine guest-induced structural transitions (lp to np state).
• Employed free energy analysis to calculate transition pressures and understand mechanisms.

Main Results:

• Identified distinct transition mechanisms: step-by-step for ELM-12 and all-at-once for DUT-8(Ni).
• Precisely determined free energy changes and transition pressures for individual MOF particles.
• Demonstrated that single-particle behavior significantly influences bulk adsorption isotherms.

Conclusions:

• Single-particle force-based analysis provides detailed insights into MOF transition mechanisms.
• This method offers a novel perspective on how particle size affects MOF performance in gas applications.
• Understanding single-particle dynamics is essential for designing efficient MOF-based gas storage and separation systems.