Controllable preparation of novel “ridge-valley shaped” poly(p-phenylene terephthamide) (PPTA) hollow fiber nanofiltration membrane for thermal dye/salt wastewater separation

In this study, two novel poly(p-phenylene terephthamide) (PPTA) hollow fiber composite nanofiltration (NF) membranes with excellent thermal stability and antifouling performance were synthesized on the homogeneous reinforced PPTA hollow fiber membranes by interfacial polymerization and the robust chemical vapor deposition separately. The effect of fabrication conditions, substrate properties on the NF performance was systematically investigated and optimized. Interestingly, SEM images presented that the two different composite membranes had relatively rough surfaces containing globular or striped structures, which was the same as the reported Turing-type structures. Meanwhile, the formation mechanism of the rough globular and striped morphologies on the surface of the membranes was also discussed. Moreover, both membranes were compared through filtration experiments such as permeate flux, solute rejection, heat stability, and anti-fouling property. The results presented that both membranes displayed high removal capacity for low molecular weight dyes (200–1000 Da), meanwhile, they exhibited high rejections (98.4 %) for negative dyes. However, they possessed complicated and diverse rejective behaviors for dye removal in different aqueous environments, such as diverse solute concentrations and diverse operating conditions. It was worth noting that PPTA/PA composite membrane showed higher separation efficiency, thermal stability, and antifouling performance compared to PPTA/PPy composite membrane, due to the significantly increased negative charge density and hydrophilicity on the membrane surface. Besides, this study offered new insights and strategies for exploring next-generation NF membranes for high temperature dye wastewater treatment.