Biporous Metal-Organic Framework with Tunable CO₂/CH₄ Separation Performance Facilitated by Intrinsic Flexibility

Area of Science:

• Materials Science
• Chemical Engineering
• Adsorption Science

Background:

• Metal-organic frameworks (MOFs) offer tunable porosity for gas separation.
• Biporous MOFs with distinct pore chemistries present opportunities for selective adsorption.
• Controlling MOF activation is crucial for optimizing material performance.

Purpose of the Study:

• To synthesize and characterize SION-8, a novel biporous MOF.
• To investigate the effect of stepwise activation on gas adsorption and separation properties.
• To evaluate the CO2/CH4 separation performance of SION-8 under different activation states.

Main Methods:

• Synthesis of SION-8 using Ca(II) and a tetracarboxylate ligand (TBAPy).
• Controlled activation of the MOF to yield partially (SION-8P) and fully activated (SION-8F) forms.
• Gas adsorption isotherms (CO2, CH4) and fixed-bed breakthrough experiments to assess separation performance.

Main Results:

• SION-8 exhibits distinct hydrophobic and hydrophilic pores.
• SION-8P shows high affinity for both CO2 and CH4, while SION-8F exhibits more pronounced CO2/CH4 affinity difference.
• SION-8F demonstrated a 40-160% increase in CO2/CH4 dynamic selectivity compared to SION-8P.

Conclusions:

• Stepwise activation of biporous MOFs can rationally tune gas separation performance.
• SION-8 offers a promising platform for selective CO2/CH4 separation.
• The intrinsic flexibility of SION-8 contributes to its complex adsorption behavior.