Chemically routed interpore molecular diffusion in metal-organic framework thin films.

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Molecular transport in porous solids typically follows Fickian diffusion along concentration gradients.
• Heterogeneous porous materials present challenges in predicting and controlling diffusion rates and directionality.
• Understanding complex diffusion pathways is crucial for optimizing material performance.

Purpose of the Study:

• To investigate molecular diffusion behavior in a model nanoporous system.
• To experimentally determine diffusion rate dependencies in heterogeneous pore structures.
• To explore the potential for controlling diffusion directionality.

Main Methods:

• Designed a model nanoporous structure using metal-organic frameworks (MOFs).
• Utilized an epitaxial, layer-by-layer growth method to create distinct, spatially oriented pore windows.
• Performed quantitative mass uptake rate measurements to analyze diffusion.

Main Results:

• Demonstrated that molecular diffusion can occur orthogonal to the concentration gradient.
• Identified interpore diffusion, perpendicular to the gradient, as the governing mass uptake mechanism.
• The MOF's specific design facilitated this non-Fickian diffusion behavior.

Conclusions:

• Molecular diffusion direction can be engineered, even against concentration gradients.
• This finding enables precise chemical carving of nanopores for enhanced diffusion.
• The study opens avenues for accelerating interpore diffusion and kinetic selectivity in porous materials.