Carbon nanotube composite membranes of brominated poly(2,6-diphenyl-1,4-phenylene oxide) for gas separation

The mechanical strength of polymeric membranes is one of the limitations in their applications. Carbon nanotubes (CNTs) are very effective in reinforcing polymeric materials, but it is unknown whether they degrade the membranes’ gas separation performance. Using brominated poly(2,6-diphenyl-1,4-phenylene oxide) (BPPOdp) as an example, we show that pristine single-wall CNTs (SWNTs) and multi-wall CNTs (MWNTs) formed polymeric nanocomposite membranes with BPPOdp. The composite membranes had an increased CO2 permeability but a similar CO2/N2 selectivity compared to the corresponding pure-polymer membrane. The CO2 permeability increased with increasing the CNT content and reached a maximum of 155 Barrer at 9 wt% of SWNTs, or 148 Barrer at 5 wt% of MWNTs. The CO2/N2 separation performance was insensitive to the MWNT diameter or length. Carboxylic acid-functionalized SWNTs (COOH-SWNTs) dispersed more uniformly in BPPOdp, and neither increased the gas permeability nor deteriorated the gas separation performance. Thus, it is feasible to add CNTs to polymeric membranes for improved mechanical strength without deteriorating the gas separation performance of the membranes. The pristine CNT-enhanced gas permeability was attributed to the formed nanogaps surrounding the CNTs.