Poly(amide-imide) (PAI) and TiO2 nanoparticle-incorporated poly(ether-sulfone) (PES) asymmetric nanofiltration membranes with an integrally dense skin layer were prepared by diffusion induced phase separation. The prepared membranes were characterized by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), atomic force microscopy (AFM), pure water flux, water content and contact angle technique to investigate the influence of PAI on the properties of the membranes. Intermolecular interactions between the components in blend membranes were established by ATR-FTIR and microcrystalline morphology was confirmed by XRD. The SEM analysis showed that blend membranes have an integrally dense skin layer adequate for nanofiltration and a spongy sub-layer along the entire membrane cross section. The contact angle measurements indicated that, hydrophilicity of the virgin PES membranes was improved by the addition of PAI and TiO2 nanoparticles due to the preferential orientation of these components towards the membrane surface during immersion precipitation. Surface free energy parameters of the membrane such as surface free energy, interfacial free energy, work of adhesion and spreading coefficient were calculated. The efficiency of these membranes in the separation of mixture solutions of divalent salt and surfactant were found to be improved significantly. Fouling stability of the membranes studied by bovine serum albumin (BSA) as the model foulant revealed improved fouling resistance. Chlorine stability of the modified membranes was also investigated. From the results, it was revealed that low interfacial free energy membranes prepared by the incorporation of PAI and TiO2 nanoparticles may be valuable in fouling stability industrial separations.
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