Tailoring the morphology of polyethersulfone/sulfonated polysulfone ultrafiltration membranes for highly efficient separation of oil-in-water emulsions using TiO2 nanoparticles

Abstract

Polyethersulfone (PES)/sulfonated polysulfone (SPSf)/TiO2 mixed matrix membranes (MMMs) were fabricated using non-solvent induced phase inversion (NIPS) technique for oil-in-water emulsion separation. The performance of the membrane was tailored by tuning the morphology through the addition of TiO2 nanoparticles (NPs) (0.05–0.15 wt %) and by varying the polymer concentrations (18–28 wt). The optimum concentration of TiO2 was found to be 0.075 wt %), where the water permeability and solute rejection trade-off neutralised. In this membrane the polymer concentration was 22 wt %. In terms of performance, the membrane had pure water permeance of 555.2 LMH bar-1, 90% oil rejection and 89.5% permeance recovery rate (PRR) at an initial concentration of 900 ppm. The surface porosity was 13.1%. Molecular dynamic (MD) simulations and spectroscopic analyses proved that the NPs formed hydrogen bonds with the polymer chains. This resulted in two effects with ripple impacts: a) slowed movement of polymer chains or slow solid-liquid phase separation, leading to the MMMs with the thicker top layer and high surface porosity, and b) stable and even distribution of NPs within the framework as observed with elemental mapping. Accordingly, the MMMs obtained desired asymmetric features corresponded to their overall superior performance. In conclusion, small concentrations of TiO2 NPs can be used to successfully modify morphology and separation performance of membranes used for oil-in-water emulsion filtration.