Effect of Positively Charged Lipids (DOTAP) on the Insertion of Carbon Nanotubes into Liposomes and the Separation Performance of Thin-Film Nanocomposite Membranes

A liposome vesicle is an ideal carrier for carbon nanotubes (CNTs) serving as the water channel that allows for the fast transport of water molecules, thus enhancing membrane permeability. However, a low quantity of CNTs inserted into the liposome vesicle is an important factor that limits the further improvement of the membrane flux. In the present study, a positively charged lipid, (2,3-dioleoyloxy-propyl)-trimethylammonium-chloride (DOTAP), was introduced to 1,2-dioleoyl-sn-glycero-3-phosphoethanolamineon (DOPE) liposome vesicles to tailor the vesicle charge so as to evaluate the effect of positively charged DOTAP on the insertion of CNTs into liposomes and the separation performance of thin-film nanocomposite (TFN) membranes. The results show that the addition of DOTAP increased the quantity of CNTs inserted into the liposome vesicles, as the shrinkage rate (k) and permeability (Pf) of the liposome vesicles presented an obvious increase with the increased content of DOTAP in the liposome vesicles. Moreover, it contributed to a 252.3% higher water flux for TFN membranes containing DOPE/DOTAP2:1-CNT liposomes (the mass ratio between DOPE and DOTAP was 2:1) than thin-film composite (TFC) membranes. More importantly, it presented a 106.7% higher water flux for TFN membranes containing DOPE/DOTAP4:1-CNT liposomes (the mass ratio between DOPE and DOTAP was 4:1), which originated from the greater number of water channels that the CNTs provided in the liposome vesicles. Overall, positively charged DOTAP effectively tailored the vesicle charge, which provided a better carrier for the insertion of a greater quantity of CNTs and contributed to the higher permeability of the TFN membranes.