A positively charged composite loose nanofiltration membrane for water purification from heavy metals

A new hybrid loose nanofiltration membrane with the positive surface charge was developed by self-assembly of Ethylenediamine (ED) grafted multi-walled carbon nanotube (ED-g-MWCNT) on the top layer of asymmetric Polyethersulfone (PES). The effects of different nanotubes loading on the membrane surface roughness, hydrophilicity, isoelectric point, and thermal and mechanical stabilities were evaluated. Due to the Donnan exclusion, the hybrid membranes exhibited excellent heavy metals rejection rates in the order of Zn (96.7%) Mg (95.01%) > Cd (92.4%) > Cu (91.9%) > Ca (91.3%) > Ni (90.7%) > Pb (90.5%). Additionally, pure water flux (PWF) of the composite membranes enhanced 122%, compared to the pure PES membrane, and achieved 80.5 L/m(2) h. Owing to the high surface hydrophilicity and minor surface roughness, the membranes antifouling properties are significantly enhanced. The overall assessment of the membranes, considering all-important factors was performed by ranking efficiency product (REP). The results indicated that the incorporation of nanotubes with a loading ratio of 0.6 wt% leads to the optimum membrane. Finally, the results of this work introduce an effective solution for water purification from heavy metal ions based on the PES nanofiltration membrane incorporated with the ED-g-MWCNT.