Polyamide thin film nanocomposite membrane incorporated with carbon nanotubes/graphene oxide for carbon dioxide removal

Abstract

Carbon capture and storage (CCS) is a feasible option to reduce the atmospheric carbon dioxide (CO2) concentration that has is rising in an alarming rate. However, the implementation of CCS is hampered by the high operating cost that is associated with CO2 removal from the emission sources. Membrane is one of the sustainable technologies that holds much potential to drive down this cost. Thin film nanocomposite (TFN) is a particularly attractive membrane as its nanomaterialembedded ultrathin selective layer could permit good separation efficiency at high rate of mass transport. Even though carbon nanotube (CNT) is a prized nanomaterial that could greatly elevate the membrane strength and separation performance, its high aggregation tendency limits its usefulness for the development of CNT-based TFN. In this study, the dispersibility of CNT was improved through amino functionalization and addition of graphene oxide (GO). Amino groups on the surface of functionalized CNT (ACNT) sterically hindered the nanotubes from bundling while the amphiphilic GO acted as dispersant that prevented clustering of the nanomaterials. This allowed successful incorporation of the nanofillers into the membrane ultrathin selective layer during interfacial polymerization (IP). The impacts of nanofillers loading, combination and ratio on IP were systematically explored. The nanomaterial s’ properties such as hydrophilicity and adsorptivity was found to affect the reactivity of IP which in turn altered the characteristics of selective layer. Gas separation results show that incorporation of ACNT improved the membrane selectivity due to its narrow openings that favor transport of the small CO2 . On the other hand, incorporation of GO led to the formation of relatively thin selective layer which improved the membrane gas permeability. Co-incorporation of ACNT with GO boosted the permeability and CO2/nitrogen selectivity of TFN by 30% and 60%, respectively, compared to the control membrane. The resulted TFN was also more reproducible and stable under elevated temperature and exposure to air. The outcome of this study suggested that synergetic incorporation of ACNT and GO provides an additional degree of freedom to control the formation of selective layer as compared to single-filler incorporation. TFN containing these two geometrically different carbon-based nanomaterials showed fascinating properties and deserves further in-depth development.