Fabrication of loose outer-selective nanofiltration (NF) polyethersulfone (PES) hollow fibers via single-step spinning process for dye removal

The textile industry is a highly polluting industry that generates a vast amount of wastewater. There is no conventional separation method that can effectively removes all the chemicals and dyes on its own. However, nanofiltration (NF) has recently demonstrated its potential to replace or complement some of the conventional methods. Nevertheless, commercially available NF membranes are predominantly fabricated by a two-step interfacial polymerization reaction on an ultrafiltration flat sheet membrane, which tends to be more laborious and complicated. In order to (1) further simplify the fabrication process and (2) exploit the advantages of the hollow fiber configuration which includes high packing density and no spacer, the fabrication of loose outer-selective NF polyethersulfone (PES) hollow fibers via a single-step spinning process for dye removal is proposed. By effectively controlling the membrane preparation process, the resultant NF hollow fiber membranes has a molecular weight cut-off of 1500 Da (pore diameter approximate to 1.96 nm) and a reasonably high pure water permeability of 13.2 LMH/bar. The newly developed NF membrane not only can effectively remove indigo carmine (M-w: 466 gmol(-1)) with a rejection greater than 94.9%, but also sustain the, high rejection during a 72 h continuous operation. Given the ease of fabrication and promising results, these PES hollow fibers may find useful applications in the treatment of textile wastewater.