Preparation and characterization of polyvinylidene fluoride/1-butyl-3-methylimidazolium bromide-based ionogel membranes for desalination applications

Polyvinylidene fluoride and an ionic liquid, 1-butyl-3-methylimidazolium bromide-based ionogel membranes, were fabricated by phase inversion method. The concentration of ionic liquid was varied in these membranes ranging from 0 to 15 wt%. The membranes were characterized by X-ray diffraction analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. The X-ray diffraction and Fourier transform infrared spectroscopy results confirmed the conversion of alpha phase of pure polyvinylidene fluoride into beta phase with the addition of ionic liquid. The thermogravimetric results exhibited an increase in thermal stability, whereas scanning electron microscopy analysis displayed an increase in porosity of the ionogel membranes with the increase in concentration of ionic liquid. These fabricated membranes were applied for desalination such as the removal of copper nitrate trihydrate and cobalt nitrate hexahydrate from water. Different membrane properties including porosity, water content, solvent content, shrinkage ratio, pure water flux, salt rejection and fouling recovery ratio were also studied for the determination of applicability of these membranes in desalination. The porosity, water content, pure water flux and fouling recovery ratio manifested an increasing trend. The solvent content decreased as we moved from less hydrophobic solvents toward more hydrophobic solvents. Shrinkage ratio also decreased with the subsequent addition of ionic liquid. All these results evidenced the efficiency of these membranes in desalination and are mainly attributed to an increase in hydrophilicity and porosity of membranes.