Fabrication of novel aromatic amine functionalized nanofiltration (NF) membranes and testing its dye removal and desalting ability

In this work, novel positively charged NF membranes, decorated with aromatic amine moieties, aminated polyphenylsulfone (PPSU-NH2) were fabricated by the phase inversion technique. The prepared membranes were characterized by scanning electron microscopy, atomic force microscopy, average pore size and molecular weight cut-off. The surface properties of these membranes were determined by ion exchange capacity (IEC), contact angle (CA), surface free energy and water spreading coefficient. The membrane enriched with an aromatic amine (M3) had an overall smoother membrane surface with a pore size of 0.72 nm M3 has a positively charged surface with an IEC of 0.51 meq.g(-1) and a highly hydrophilic nature confirmed by a low water CA (similar to 31 degrees), and the greatest observed pure water flux (similar to 54 LMH). The amine incorporated membranes showed an increased resistance to fouling when challenged with cetyl trimethyl ammonium bromide as a model foulant, which suggests the existence of repulsive forces shielding the membranes from the positively charged foulants. The M3 showed a considerable rejection of 89 and 93.5% for the multivalent salts CaCl2 and AlCl3, respectively, and expectedly lower rejection of 18.7 and 25.6% for univalent salts Na2SO4 and NaCl, respectively. The prepared membranes demonstrated an exceptional ability in rejection ( > 99%) of cationic dye crystal violet while maintaining a moderate flux. Therefore, this method of preparation of a positively charged NF membrane can be further investigated for its potential for the removal of dyes and metal ions from commercial waste streams.