Abstract
•Presence of heavy metals in industrial wastewater poses an environmental risk.•Polyethersulfone/Carbon Nanotubes/Polyvinyl alcohol membranes were synthesised.•Infusion of CNTs improved metal rejection and membrane flux.•Polyvinyl alcohol coating improved membrane hydrophilicity and rejection.•The optimum membranes showed potential application for wastewater treatment.
Polyethersulfone (PES) is commonly used to fabricate ultrafiltration (UF) membranes applied during the treatment of wastewater due to its high permeability and tensile properties, chemical and thermal stability. However, PES has low hydrophilicity due the sulfonyl functional group and therefore becomes susceptible to fouling, resulting in reduced membrane performance and lifespan. In this study, 10 wt% PES/CNT membranes were prepared by infusing 2.5, 5, 7.5 and 10 wt% Carbon nanotubes (CNTs) into PES to produce PES/2.5 wt% CNT, PES/5 wt% CNT, PES/7.5 wt% CNT and PES/10 wt% CNT membranes by phase inversion. The membranes were immersed in 1 wt% PVA solution to coat a hydrophilic PVA layer on the surface of the membranes to fabricate PES/2.5 wt% CNT/PVA, PES/5 wt% CNT/PVA, PES/7.5 wt% CNT/PVA and PES/10 wt% CNT/PVA membranes. A 10 wt% pure PES reference membrane was also prepared for comparison purposes. This research focused on evaluating the effect of coating a PVA layer on the performance of a PES/CNT/PVA membrane. TEM characterization revealed that the CNTs are MWCNT, PSD was done to obtain CNT particle size, FTIR confirmed the formation of –COOH and –OH functional groups on the surface of CNTs, SEM confirmed porous membrane structures, BET showed an increase in pore size at higher CNTs loading, tensile properties showed a decrease when CNTs were added, and contact angle studies showed significant increase in hydrophilicity with the addition of CNTs and PVA. Filtration experiments were conducted using a dead-end stirred cell. PES/7.5 wt% CNT/PVA showed the most improved results with a good trade-off balance between membrane flux and rejection, generating a flux of 7.94 L/m2h and rejection of 88.56% Cu2+, 96.15% Fe2+, 89.06% Ni2+, 100% Zn2+ and 99.93% Cl−. Anti-fouling tests for PES/7.5 wt% CNT/PVA conducted using a cross-flow filtration rig showed that only 70.77% of the flux could be recovered. These results showed that a PES membrane that has been infused with functionalized CNTs and coated with a layer of PVA membrane can effectively remove Cu2+, Fe2+, Ni2+, Zn2+ and Cl− from industrial wastewater.