Abstract
The present work reports on the gas transport behavior of mixed matrix membranes (MMM) which were prepared from multi-walled carbon nanotubes (MWCNTs) and dispersed within polymers of intrinsic microporosity (PIM-1) matrix. The MWCNTs were chemically functionalized with poly(ethylene glycol) (PEG) for a better dispersion in the polymer matrix. MMM-incorporating functionalized MWCNTs (f-MWCNTs) were fabricated by dip-coating method using microporous polyacrylonitrile membrane as a support and were characterized for gas separation performance. Gas permeation measurements show that MMM incorporated with pristine or functionalized MWCNTs exhibited improved gas separation performance compared to pure PIM-1. The f-MWCNTs MMM show better performance in terms of permeance and selectivity in comparison to pristine MWCNTs. The gas permeances of the derived MMM are increased to approximately 50% without sacrificing the selectivity at 2 wt.% of f-MWCNTs' loading. The PEG groups on the MWCNTs have strong interaction with CO2 which increases the solubility of polar gas and limit the solubility of nonpolar gas, which is advantageous for CO2/N2 selectivity. The addition of f-MWCNTs inside the polymer matrix also improved the long-term gas transport stability of MMM in comparison with PIM-1. The high permeance, selectivity, and long term stability of the fabricated MMM suggest that the reported approach can be utilized in practical gas separation technology.
Highlights
During the last two decades, significant improvements in the performance of polymeric materials for gas separation membranes have been made [1,2,3,4,5,6], and understanding of the relationships between the polymer structure and gas transport properties of polymeric membranes has been greatly advanced [2,3]
The pristine and functionalized multi-walled carbon nanotubes (MWCNTs) were characterized by Thermal gravimetric analysis (TGA) and Fourier transform infrared (FTIR)
The scanning electron microscopy (SEM) images of the prepared matrix membranes (MMM) revealed that the functionalized MWCNTs are well dispersed throughout the polymer of intrinsic microporosity (PIM)-1 matrix compared to the one which is fabricated from pristine MWCNTs
Summary
During the last two decades, significant improvements in the performance of polymeric materials for gas separation membranes have been made [1,2,3,4,5,6], and understanding of the relationships between the polymer structure and gas transport properties of polymeric membranes has been greatly advanced [2,3] Despite these advantages and progresses, polymeric membranes are restricted by the trade-off trend between gas permeability and selectivity, as shown by Robeson [7]. In their results both the permeabilities and the selectivities of H2, CO2, and CH4 improved significantly at high MWCNTs concentrations (>5 wt.%) Based on these investigations, one can conclude that the interaction between polymer matrix and nanotubes may disrupt the polymer chain packing enhancing gas diffusion due to introducing more free volume voids between the polymer chains and nanoscale defects on the polymer/nanofillers interface
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