Facilitated transported composite membranes were synthesized for efficient CO2/N-2 separation by incorporation surface modified multi-walled carbon nanotubes (CNTs) in polyvinyl alcohol (PVA) and adjusting the pH of the membrane casting solution from acidic to basic. The membranes were developed for post-combustion CO2 capture operating under humidified condition and low CO2 partial pressure. The membrane was tailored by adding different concentrations of surface modified CNTs (0-2%) with respect to PVA and adjusting pH from 5 to 12. An optimal CNT loading along with membrane pH was determined based on experimental results from gas permeation tests. By optimizing the CNT loading and pH of the membrane, the CO2 permeance was increased from 0.18 +/- 0.02 m(3) (STP)/m(2) bar h to 0.44 +/- 0.02 m(3) (STP)/m(2) bar h at a constant CO2/N-2 selectivity of 60 +/- 1. The membrane swelling degree was also increased from 154 20 to 254 30. The thickness of the selective layer was reduced from similar to 0.85 mu m to 0.45 mu m which resulted in further increase in permeance to 0.48 m(3) (STP)/m(2) bar h. The developed membrane showed a stable operation over a period of 1 month.(C) 2017 Elsevier B.V. All rights reserved.