Increased CO₂ Affinity and Adsorption Selectivity in MOF-801 Fluorinated Analogues

Area of Science:

• Materials Science
• Chemistry

Background:

• Metal-organic frameworks (MOFs) offer tunable porosity for gas adsorption.
• Perfluorinated linkers can modify MOF properties, but their impact on porosity and adsorption needs further investigation.

Purpose of the Study:

• To synthesize and characterize a novel Zr(IV)-based perfluorinated MOF (ZrTFS) using tetrafluorosuccinic acid (H2TFS).
• To investigate the effect of incorporating fluorinated linkers into MOF-801 via postsynthetic exchange (PSE) on CO2 and N2 adsorption.
• To elucidate the structural and thermodynamic factors governing CO2 adsorption in these materials using DFT calculations.

Main Methods:

• Solvent-free synthesis of ZrTFS.
• X-ray powder diffraction for structural analysis.
• Postsynthetic exchange (PSE) reactions to create mixed-linker MOFs (PF-MOF1, PF-MOF2).
• Gas adsorption measurements (CO2, N2) to determine adsorption capacity and selectivity.
• Solid-state density functional theory (DFT) calculations.

Main Results:

• ZrTFS was synthesized and found to be isoreticular to MOF-801, but with reduced porosity due to bulky fluorine atoms.
• PSE reactions successfully incorporated H2TFS linkers into defective MOF-801 sites, forming PF-MOF1 and PF-MOF2.
• CO2 adsorption affinity (Qst) and CO2/N2 selectivity increased with higher TFS content, reaching optimal values in PF-MOF2 (30 kJ/mol and 41 IAST, respectively).
• DFT calculations identified preferential CO2 adsorption sites and highlighted the role of hydrogen bonding.

Conclusions:

• Perfluorinated linkers can enhance CO2 adsorption properties of MOFs.
• Postsynthetic exchange is an effective strategy to introduce fluorinated linkers and improve MOF performance for CO2 capture.
• The study provides insights into structure-adsorption relationships for designing advanced gas separation materials.