Superhydrophobic PVDF–PTFE electrospun nanofibrous membranes for desalination by vacuum membrane distillation

Abstract

In this study, a superhydrophobic nanofibrous membrane was prepared on the basis of an electrospun polyvinylidene fluoride (PVDF)–polytetrafluoroethylene (PTFE) nanofibrous scaffold coupled with a microporous PTFE substrate. The PVDF–PTFE nanofibrous scaffold was fabricated by electrospining of PVDF–PTFE blend solutions, it was observed that by changing the PTFE micro-powder content in the dope solutions from 0wt.% to 12wt.%, the water contact angle (WCA) and the liquid entry pressure (LEPw) of the membrane vary from 130.4° and 84kPa to 152.2° and 137kPa, respectively. The superhydrophobic PVDF–PTFE nanofibrous membrane was then tested for desalination by vacuum membrane distillation (VMD), a stable flux of 18.5kg/m2h and salt rejection higher than 99.9% was presented throughout the entire testing period of 15h, indicating the great potential of the PVDF–PTFE nanofibrous membranes in VMD. For further application of the PVDF–PTFE nanofibrous membranes in VMD, a mathematical model was presented to predict the vapor flux of the novel membrane under various operation conditions. A good agreement between the experimental and theoretical values for vapor fluxes was obtained; the results indicated that the VMD flux increased with the increase of feed temperature and flow rate and decreased with the increase of permeate pressure.