Facile pore structure control of poly(vinylidene fluoride) membrane for oil/water separation

摘要

Traditional fabrication of poly(vinylidene fluoride) (PVDF) microfiltration (MF) membranes used in oil/water emulsion separation has yet to overcome the challenging trade-off relationship between permeability and selectivity. Herein, we proposed a facile approach to fabricate a PVDF microfiltration membrane with high flux and highly controllable pore structure for effective oil/water emulsion separation, utilizing a unique quaternary PVDF/MgCl2/PVP/DMAc system featuring a lower critical solution temperature (LCST) without any thermosensitive polymer. FTIR analysis indicated the molecular interaction amongst the four components and the LCST hypothesis was proposed. Combined with an unconventional nonsolvent thermally induced phase separation (NTIPS) method, a unique skinless surface and macrovoid-free pore structure of the membrane were achieved by simply tuning the water coagulation temperature to below or above the LCST of the selected solution system, i.e. 50 degrees C. The membrane produced at 70 degrees C, namely N70, exhibited superior filtration performance in both pure water testing with an ultrahigh flux of 6870 L m(-2) h(-1) bar(-1), and filtration of surfactant-stabilized oil/water emulsion in terms of superior permeability of 1608 L m(-2) h(-1) bar(-1) and 99.1% rejection of oil contaminants. The membrane permeability was 5.5-fold higher than that of the membrane produced below LCST, without compromising the rejection properties. Preliminary fouling studies show that the N70 exhibited the lowest resistance to oil fouling and hence the highest flux recovery. Thus, the proposed strategies bring new perspectives in preparing an ideal membrane for water purification to overcome the trade-off between high flux and high rejection properties. The concept can be extended to the fabrication of membranes with controllable structure in the broader separation and purification field.