Studies on the porosity control of MWCNT/polysulfone composite membrane and its effect on metal removal

Functionalized multi-walled carbon nanotube/polysulfone (MWNT/PSf) composite membranes were synthesized by the phase inversion method using DMF as solvent and water with isopropanol as coagulant. The membrane characteristics when evaluated by capillary porometry showed reduced pore size depending on the type of functionalities on the nanotubes. Three different functionalities were generated on the nanotube surface i.e., oxidized, amide and azide. The MWNT/PSf composite membranes appeared to be more hydrophilic, with a reduced flux, and lower flow rate than the pure polysulfone (PSf) membranes. The amount of MWNTs in the composite membranes was an important factor affecting the morphology, and permeation properties of the membranes. The composite membranes also showed enhanced thermal stability as found from thermogravimetric analysis. Heavy metal rejection on the composite membranes gave interesting results. The percent rejection of heavy metal was found to increase with increase in amount of MWNTs and best results were obtained at a pressure of 0.49 MPa and in an acidic pH of 2.6. Amide functionalized CNT/PSf composite membranes gave 94.2% removal for Cr(VI) and 78.2% removal for Cd(II) which was just 10.2% and 9.9%, respectively, with unblended plain polysulfone membranes.

► Functionalized MWNT/polysulfone membranes process gave control on the membrane morphology.
► The MWNT/PSf composite membranes were more hydrophilic with a reduced flux and flow rate.
► Pore size and contact angle reduced with increasing percentage of nanotubes.
► Optimum conditions are 4.9 bar pressure and pH 2.6 for maximum rejection of heavy metals.
► Heavy metal rejection was the highest (94.2%) for amide functionalized MWNT/PSf composite membranes.