MOF Pore Sieving | mysimulator.uk

Framework Tuning

Pore aperture 4.2 Å

Temperature 298 K

Adsorption energy 22 kJ/mol

Gas Mixture

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CO₂ : N₂ selectivity (adsorbed fraction ratio)

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How it works

A metal-organic framework (MOF) is a crystalline lattice of metal-ion nodes linked by rigid organic struts, enclosing regular nanopores. Swapping the linker length changes the pore's aperture — the narrowest opening a diffusing molecule must pass through — which is exactly how real frameworks like ZIF-8 (aperture ≈ 3.4 Å) achieve molecular sieving.

Each gas molecule here carries its real kinetic diameter (CO₂ 3.30 Å, N₂ 3.64 Å, CH₄ 3.80 Å). Near an open metal site it can adsorb with a site-blocking (Langmuir) probability per step:

p_ads ∝ f(aperture − d_molecule) · exp(−Eads / RT)
f = 0 for aperture < d_molecule   (size-excluded)
f → 1 as aperture − d_molecule grows

A smaller aperture sieves out the larger molecule entirely regardless of energy — pure size exclusion. A larger aperture admits everything, and selectivity is then set only by the Boltzmann factor exp(−E_ads/RT): a deeper binding well and a lower temperature both raise occupancy and residence time, mirroring real MOF gas-separation performance (e.g. CO₂/N₂ capture from flue gas).

Pore aperture — narrows or widens the sieving window between unit cells.
Temperature — raises molecular speed and desorption rate (residence time ∝ exp(E/RT)).
Adsorption energy — the physisorption well depth at each open metal site.
Species toggles — add or remove a gas from the mixture entirely.

Framework node (metal cluster) CO₂ N₂ CH₄

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MOF Pore Sieving: Selective Gas Adsorption