Preparation of polysulfone–polyamide thin film composite hollow fiber nanofiltration membranes and their performance in the treatment of aqueous dye solutions

Thin film composite hollow fiber nanofiltration membranes containing poly(m-phenylene-trimesamide) active layer on polysulfone ultrafiltration membrane were prepared by in situ interfacial polymerization between m-phenylenediamine and trimesoyl chloride under different conditions. The nanofiltration membranes exhibited molecular weight cut-off values in the range of 490 to 730 g/mole. They showed the rejections in the range of 60–97% for reactive black-5 and rhodamine-B with water flux of 10–35 mL/m2 h at 25 psi for feed solutions containing 400–2000 ppm dye. The flux was decreased slightly while the rejection was remained almost the same upon increasing the dye concentration from 400 ppm to 2500 ppm in feed. The dye rejection and flux of the membranes were found to be reduced by 2–5% when tested with feed solutions containing a mixture of dye and NaCl (up to 10,000 ppm). This may be attributed to either the decrease in Donnan's exclusion effect or change in membrane pore structure by salting out or by pore swelling effect. The membranes were characterized by SEM and AFM for surface morphology. The surface roughness was found to be in the range of 20 to 40 nm, as observed by AFM, depending upon polyamide preparation conditions.