2.3.2. Fabrication of Elvaloy4170 /MWNTs mixed matrix membranes
Except for the composition and preparation procedure of the dope, other processes for the MMMs fabrication were similar to the pure polymer membranes. The dope preparation procedure of the MMMs was as follows. Three grams of Elvaloy4170 was dissolved in 14 g of toluene and mixed and heated at 50 °C for 1 day to prepare the polymer solution with a composition of 3:14 (Elvaloy4170:toluene). Since CNTs are highly susceptible to water adsorption, they were dried in an air circulating oven at 100 °C overnight prior to use. Next, a predetermined amount (1, 2, 3 or 4 wt.% solid base) of r-MWNTs or f-MWNTs was added to 3 g of toluene and the mixture was sonicated for 15 min at room temperature in order to break nanotubes aggregation and enhance their dispersion quality in toluene. Immediately afterward, the nanotubes dispersion was added all at once to the prepared polymer solution. The resulting solution composed of Elvaloy4170, MWNTs, and toluene was further stirred at 50 °C for 6 h to obtain a homogeneous viscous solution. Following this time period, the mixture was re-sonicated for 50 min at 50 °C to provide effective dispersion of MWNTs and degas the mixture. As-prepared solution was then kept under vacuum at 60 °C for 15 min to ensure the complete removal of gas bubbles that may exist in the dope. After degassing, the membranes were cast onto a Teflon plate using a casting knife with 300 μm thickness. For all dope solutions, Elvaloy4170 to toluene/MWNTs mixture ratio was 15:85, but the ratio of Elvaloy4170 to MWNTs was varied; 99.0:1.0, 98.0:2.0, 97.0:3.0 and 96.0:4.0. Hereafter, the contents of MWNTs with respect to Elvaloy4170 will be used throughout the paper. Table 3 represents the dope compositions of MMMs. The drying procedure for the MMMs was identical to that of the neat polymer membrane.