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In this study, the gas separation performance of polysulfone (PSF) hollow fiber mixed matrix membranes (MMMs) incorporated with nanotubes derived from titania were investigated. Titania nanotubes (TNTs) were synthesized via facile hydrothermal method of different reaction times: 10 h and 48 h. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and BET analysis were conducted to scrutinize the structural morphology of the as-synthesized TNTs. TNTs produced under prolonged reaction exhibited larger tube diameters, but have rather smaller pores. No functionalizations or modifications were made regarding the surface chemistry of the TNTs prior to blending with the spinning dope. Defect-free membranes were attained up to 0.6 wt% addition of TNT10. The measured permeances for all gases tested were profoundly increased with the addition of TNTs. PSF-TNT10 0.4 wt% MMM recorded the highest permeance enhancement (about 150%), with H2, CO2, O2 permeance of 269 GPU, 120 GPU, and 26 GPU, respectively, with O2/N2, H2/CH4, CO2/CH4, and CO2/N2 selectivity remained higher than the neat membrane. TNT48 MMM demonstrated relatively lower fluxes but higher selectivity which ascribed to its smaller internal tube diameter endowing better size-exclusion capability. The TNTs formation mechanisms were discussed to justify the evolution of gas separation performance of TNT-incorporated MMMs. In light of the findings, hydrothermal method can be regarded as a versatile technique for producing TNTs of different morphologies simply by manipulating its reaction parameters. On top of that, TNTs being a low cost material, it holds enormous potential to be widely exploited in gas separation applications.

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.