Asymmetric hollow fiber membrane coated with polydimethylsiloxane–metal organic framework hybrid layer for gas separation

• Multicomponent composite/hybrid asymmetric membrane was prepared.
• Hollow fiber membrane was coated by PDMS containing Cu3(BTC)2 MOF.
• Cu3(BTC)2 particle was homogeneously embedded in the PDMS coating layer.
• Composite membranes showed higher permeance and selectivity.

This study presents an alternative approach to improve the gas separation performance of conventional asymmetric membranes. For the first time, multicomponent composite/hybrid asymmetric membrane was prepared by unifying two prominent concepts in gas separation membranes: (1) sealing or caulking asymmetric membrane imperfections by means of coating a highly permeable polymer layer, and (2) the incorporation of selective inorganic particle in polymer matrix generally known as the mixed matrix membrane. Asymmetric hollow fiber membranes (polysulfone (PSF)) was externally coated by polydimethylsiloxane (PDMS) solution containing suspended Cu3(BTC)2 metal organic framework (MOF) by dip-coating technique. FESEM–EDS mapping confirmed the increase in Cu3(BTC)2 adherence with increasing number of coating. The pure gas permeation experiment with CO2, N2 and CH4 corroborated the contribution of Cu3(BTC)2 particle to the overall composite/hybrid membrane performance. The gas permeation rates were increased with increasing number of PDMS–Cu3(BTC)2 coating applied. CO2 permeance increased from 69.7 to 109.2 × 10−6 cm3 (STP)/cm2 s cmHg after 5 consecutive coatings. In addition, the CO2/CH4 and CO2/N2 selectivities were found to be increased as well. Cu3(BTC)2 contributed to higher affinity toward CO2 due to the coordinatively unsaturated copper sites in its crystal network, which provide exceptionally high adsorptive capability for polar molecules, hence resulted in the increase of the overall selectivities and gas permeation rates across the membrane. Further development based on this study will create vast opportunities for future improvement on any commercially available gas separation membranes by implementing the method described herein.

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