Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal Dual-layered electrospun nanofibrous membranes for membrane distillation M. Khayet a,b,⁎ , M.C. García-Payo a , L. García-Fernández a , J. Contreras-Martínez a a Department of Applied Physics I, Faculty of Physics, University Complutense of Madrid, Avda. Complutense s/n, 28040 Madrid, Spain b Madrid Institute of Advances Studies of Water (IMDEA Water Institute), Avda. Punto Com No 2, 28805, Alcalá de Henares, Madrid, Spain GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Dual-layer Electrospinning Nanofiber Desalination Membrane distillation ABSTRACT Dual-layered electrospun nanofibrous membranes (DL-ENMs) were prepared using the hydrophobic polymer polyvinylidene fluoride (PVDF) and the hydrophilic one polysulfone (PSF). The thickness of each layer was varied by changing the electrospinning time of each polymer solution maintaining the total electrospinning time at 3 h. The characteristics of the DL-ENMs and those of each layer were studied by means of different techniques and the results were compared to the single layer PVDF and PSF ENMs (i.e. SL-ENMs). The prepared DL-ENMs were tested in desalination by direct contact membrane distillation (DCMD) using different sodium chloride feed aqueous solutions. The DCMD permeate flux of the DL-ENMs was found to be higher than that of the PVDF SL- ENM and it increased with the decrease of the PVDF layer due not only to the reduction of the total thickness and to the increase of both the inter-fiber space and the void volume fraction, but also to the reduction of the path between the liquid/vapour interfaces formed at both side of the DL-ENMs. Compared to the proposed SL-ENMs in DCMD, it is better to use DL-ENMs adequately designed with hydrophobic and hydrophilic polymers than SL- ENM with only a hydrophobic polymer. 1. Introduction Nanofibrous materials exhibit several important characteristics such as a very high surface area to volume ratio that can be as high as 100 times that of microfibrous materials, tunable and very high void volume fraction or “porosity” that can reach > 90%, inter-fiber space or “pore size” that can range from ten nanometers to several micrometers, flexibility in surface functionalities, interconnected open structure, good mechanical performance and possibility to construct a wide variety of fiber sizes and shapes (e.g. beaded, ribbon, porous and core- shell nanofibers). Therefore, nanofibrous materials have received ex- tensive research interest for many potential applications in diverse http://dx.doi.org/10.1016/j.desal.2017.10.036 Received 1 August 2017; Received in revised form 21 October 2017; Accepted 22 October 2017 ⁎ Corresponding author at: Department of Applied Physics I, Faculty of Physics, University Complutense of Madrid, Avda. Complutense s/n, 28040 Madrid, Spain. E-mail address: khayetm@fis.ucm.es (M. Khayet). Desalination 426 (2018) 174–184 Available online 10 November 2017 0011-9164/ © 2017 Elsevier B.V. All rights reserved. MARK