Relating the performance of sulfonated thin-film composite nanofiltration membranes to structural properties of macrovoid-free polyethersulfone/sulfonated polysulfone/O-MWCNT supports

Sulfonated thin-film composite nanofiltration (TFC NF) membranes were produced on macrovoid-free polyethersulfone/sulfonated polysulfone/oxidised multi-walled carbon nanotube (PES/SPSf/O-MWCNT) supports via an interfacial polymerisation method. The aqueous phase solution consisted of a mixture of piperazine (PIP) and 2,4-diaminobenzene sulfonic acid (2,4-DABSA) and the organic phase solution consisted of trimesoyl chloride (TMC). The TFC NF membranes fabricated on the PES/SPSf/O-MWCNT supports showed a 35% improvement in pure water flux with comparable salt rejections from those prepared on PES/SPSf supports. The presence of hydrophilic O-MWCNTs in the PES/SPSf supports resulted in the formation of a thin polyamide film on the surface of the support with enhanced water permeability and salt rejection. The addition of low monomer weight ratio of 2,4-DABSA in the diamine aqueous mixture led to the generation of sulfonated TFC NF membranes with superior membrane performance in terms of pure water permeability (30.2 L/m2·h·bar), monovalent/bivalent salt selectivity (αNaCl/Na2SO4 = 25.0) at low operating pressures (3 bar) and at salt concentrations in the range of brackish waters. Moreover, the fabricated sulfonated TFC NF membranes exhibited good antifouling properties against bovine serum albumin, with a flux recovery ratio of 96.4% obtainable after three cycles of fouling and cleaning. The performance of the sulfonated TFC NF membranes remained fairly stable over a 10-day period of pure water flux and Na2SO4 salt rejection testing. The fabricated sulfonated TFC NF membranes displayed promising features for use as pre-treatment membranes for lower-pressure water softening and desalination of brackish water.