Fabrication and characterization of a high performance polyimide ultrafiltration membrane for dye removal

Membrane separation technology is one of the cost effective and most efficient technologies for treatment of wastewater from textile industry. However, development of membranes with better performance and thermal stability is still a highly challenging task. In this study, successful preparation of a novel thermally stable polyimide (PI) polymer was demonstrated using 2,4,6-trimethyl-1,3-phenylenediamine, 4,4'-diaminodiphenylmethane and 1,2,4,5-benzenetetracarboxylic dianhydride components. PI was selected as representative candidate because of its excellent thermal stability (decomposition temperature of 529 °C), as revealed by thermogravimetric analysis. Furthermore, PI polymer was used to fabricate ultrafiltration (UF) membrane by phase inversion process. This UF membrane is especially interesting as it allowed for almost complete penetration of monovalent (NaCl) and divalent (Na₂SO₄) inorganic salts because of its molecular weight cut off of 9320 Da. Moreover, the membrane exhibited very good surface hydrophilicity with the water contact angle of 67.6°. This PI-based UF membrane was found to be substantially effective as it showed high pure-water and dye-permeation fluxes of 345.10 and 305.58 L m^-2 h^-1 at 0.1 MPa, respectively. Besides, the membrane exhibited a rejection of 98.65% toward the direct red 23 dye (100 ppm) at 0.1 MPa. Thus, this PI-based UF membrane is highly beneficial and acts as a potential candidate for dye removal from wastewater produced by textile industry.