The Effect of Cross-Linkers on the Permeability of Electrically Conductive Membranes

Microfiltration (MF) and ultrafiltration (UF) electrically conductive membranes (ECMs) were fabricated by coating MF and UF poly(ether sulfone) membranes, respectively, with a thin conductive film of cross-linked functionalized single-and double-walled carbon nanotubes. The thin film was composed of a reacted network of carbon nanotubes, poly(vinyl alcohol), and dicarboxylic cross-linkers. We analyzed the impact of cross-linker lengths, mass of CNTs, and cross-linking degree on the thin conductive film's electrical conductivity, pore size, porosity, surface hydrophilicity, and the resultant ECM transmembrane flux. It was found that conductive thin films containing longer cross-linkers increased transmembrane flux in MF and UF membranes by up to 187% and 254%, respectively, over control non-cross-linked membranes. Control MF and UF CNT membranes had average permeabilities of 1008 and 97 LMH/bar. Cross-linked membranes achieved an average permeability of 2901 and 344 LMH/bar, respectively. The bulk electrical conductivity was shown to be affected by both the presence of cross-linkers as well as the thickness of the thin film. Longer cross-linkers in MF and UF ECMs enhanced electrical conductivity by up to 61% and 440% as compared to control non-cross-linked MF and UF ECMs, respectively. Morphology of the membrane, wetting properties, surface roughness, and presence of covalent bonds were investigated using SEM, pendant-drop contact angle test, AFM, and FTIR, respectively.