Effect of Salt Additives on the Fabrication of Poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) Nanofiber Membranes for Air Gap Membrane Distillation

Abstract

In the past few years, application of electrospun nanofiber has gained intensive attention for membrane distillation (MD) that exhibit promising results. In this study the effects of three salt additives including calcium carbonate (CaCO₃), lithium chloride (LiCl) and calcium chloride (CaCl2) on the morphology, hydrophobicity, porosity and permeation performance of poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP) nanofiber membranes were investigated. Scanning electron microscopy (SEM), geniometer, gravimetric method and air gap MD (AGMD) setup were used to characterize the resultant PVDF-HFP membranes. It was observed that addition of LiCl and CaCl₂ improved the electrospinability of polymer dope solution and changes the morphology of fibers from beaded fiber to a uniform fiber structure. Also the membrane made from the dope with LiCl as the additive salt possessed the highest porosity of % 89. The membrane hydrophobicity was affected less by CaCO₃ as compared with LiCl and CaCl₂. The synthesized membrane was applied in desalination via air gap membrane distillation, in which a water permeation flux of 13.6, 12.2 and 9.8 Lh^-1m^-2 were obtained when LiCl, CaCl₂ and CaCO₃ was used as the additive, respectively.