Gas separation performance of ultra-permeable graphene oxide membranes supported by single-wall carbon nanotubes: Unveiling the effect of fabrication method, gas flow transport type, and material aging

This study comprehensively investigated the impact of the preparation method on the resulting material properties of self-standing graphene oxide (GO) membranes and GO membranes deposited on a single-walled carbon nanotube (SWCNT) support layer, which was carried out using SEM, XRD, XPS, Raman and FTIR spectroscopy, 3D profilometry, thermal analysis and physisorption characterisation. The analysis of the gas permeability and separation properties of the membranes (including the effect of ageing) performed by repeated time-lag measurements of individual gases revealed a gradually increasing permeability and ideal selectivity, probably due to the release of residual water from the mother liquor. Samples prepared by the evaporation or vacuum filtration method exhibited a relatively short lifetime (up to 100 h), high H₂ permeability (up to 12,000 Barrers), and ideal H₂/CO₂ selectivity from 2 to 3. In contrast, membranes prepared by the pressure filtration method showed durable character for almost 800 days while showing huge and increasing permeability exceeding 100,000 Barrers and, at the same time, remarkable selectivity for H₂/CO₂ (more than 4) and H₂/CH₄ (around 2) gas vapors, over the 2008 Robeson upper bound limit. The transport analysis performed via the Binary Friction Model revealed the predominant type of gas transport as Darcy flow rather than Knudsen type. Our work demonstrates the potential of GO-SWCNT membrane materials for developing new advanced separation membranes for future efficient gas, vapor, or liquid separation technologies.