Robust PVDF/PSF hollow-fiber membranes modified with inorganic TiO2 particles for enhanced oil-water separation

HPollow-fiber (HF) membranes with high tensile strength and water permeance and composed of poly(vinylidene fluoride) (PVDF) and polysulfone (PSF) were prepared using phase inversion to enhance separation of oil-in-water (O/W) emulsions. Hydrophilic inorganic particles of titanium dioxide (TiO₂) were coated onto PVDF/PSF membrane surfaces with the aid of Pluronic and polydopamine (PDA). The pore structure, hydrophilic properties, and tensile strength of HF membranes can be finely tuned by varying the TiO₂ concentration in the coating solution. Pluronic or PDA-assisted TiO₂ coating enhanced the adhesion between TiO₂ and membrane surface as revealed by X-ray photoelectron spectroscopy and stability tests. These HF membranes achieved enhanced O/W emulsion separation in a crossflow filtration process. A Pluronic-stabilized HF membrane achieved a higher rejection rate (above 99.5%) and stable permeance (∼650 Lm^-2 h⁻¹ bar⁻¹) in a micro-sized emulsion (soybeans-in-water) at a TiO₂ concentration of 0.75 wt% compared with a pristine HF membrane. Meanwhile, PDA-stabilized HF membranes exhibited 99% rejection and stable permeance of 410 Lm^-2 h⁻¹ bar⁻¹ toward nano-sized emulsion (hexane-in-water) when the PDA@TiO₂ composite concentration was 0.75 wt%, while a pristine HF membrane achieved a rejection rate of only ∼90% and a permeance <200 Lm^-2 h⁻¹ bar⁻¹. The enhanced hydrophilicity and decorated pore structure produced by hydrophilic TiO₂ with the aid of polymers (Pluronic or PDA) enhanced the separation performance of both micro- and nano-sized O/W emulsions through HF membranes.