Dual-layered electrospun nanofibrous membranes for 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 SLENM 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 SLENM with only a hydrophobic polymer.