Electrospun dual-layer nonwoven membrane for desalination by air gap membrane distillation

In the present study, dual-layer nanofiber nonwoven membranes were prepared by a facile electrospinning technique and applied for desalination by air gap membrane distillation (AGMD). Neat single and dual-layer nanofiber membranes composed of a hydrophobic polyvinylidene fluoride-co-hexafluoropropylene (PH) top layer with different supporting hydrophilic layer made of either polyvinyl alcohol (PVA), nylon-6 (N6), or polyacrylonitrile (PAN) nanofibers were fabricated with and without heat-press post-treatment Surface characterization showed that the active layer (i.e., PH) of all electrospun nanofiber membranes (ENMs) exhibited a rough, highly porous (>80% porosity), and hydrophobic surface (CA > 140 degrees), while the other side was hydrophilic (CA < 90 degrees) with varying porosity. Heat-pressing the membrane resulted to thinner thickness (from >129 mu m to <100 mu m) and smaller pore sizes (<0.27 mu m). The AGMD experiments in a co-current flow set-up were carried out with constant inlet temperatures at the feed and permeate streams of 60 +/- 1.5 and 20 +/- 1.5 degrees C, respectively.TheAGMD module had a membrane area of 21 cm(2) and the thickness of the air gap was 3 mm. The neat single and dual-layer ENMs showed a water permeate flux of about 10.9-15.5 L/m(2) h (LMH) using 3.5 wt% NaCl solution as feed, which was much higher than that of a commercial PVDF membrane (similar to 5 LMH). The provision of a hydrophilic layer at the bottom layer enhanced the AGMD performance depending on the wettability and characteristics of the support layer. The PH/N6 dual-layer nanofiber membrane prepared under the optimum condition showed flux and salt rejection of 15.5 LMH and 992%, respectively, which has good potential for AGMD application. (C) 2015 Elsevier B.V. All rights reserved.