Water Adsorption and Insertion in MOF-5

Area of Science:

• Materials Science
• Chemical Physics
• Computational Chemistry

Background:

• Metal-organic frameworks (MOFs) offer high surface areas and tunable properties, making them promising for catalysis and gas management.
• However, the limited hydrolytic stability of some MOFs hinders their practical application in humid environments.
• Understanding MOF hydrolysis mechanisms is crucial for designing water-stable materials.

Purpose of the Study:

• To elucidate the atomic-scale mechanisms governing MOF hydrolysis under humid conditions.
• To investigate the thermodynamics and kinetics of water adsorption and insertion into MOF-5.
• To provide insights for developing robust MOFs resistant to water degradation.

Main Methods:

• Utilized van der Waals-augmented density functional theory (DFT).
• Employed transition-state finding techniques and thermodynamic integration.
• Analyzed water adsorption/insertion energetics in MOF-5 without structural approximations.

Main Results:

• MOF hydrolysis thermodynamics are coverage-dependent.
• Water insertion into MOF-5 becomes exothermic only after sufficient co-adsorbed water clusters form.
• A low free-energy barrier (0.17 eV at 0 K, 0.04 eV at 300 K) for water insertion was calculated above the coverage threshold.
• Co-adsorbed water clusters facilitate Zn-O bond breaking, driving hydrolysis.

Conclusions:

• The study provides a realistic atomic-level understanding of MOF hydrolysis mechanisms.
• Water co-adsorption plays a critical role in initiating MOF framework degradation.
• Findings can guide the rational design of hydrolytically stable MOFs for practical applications.