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

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 0 wt.% to 12 wt.%, the water contact angle (WCA) and the liquid entry pressure (LEPw) of the membrane vary from 130.4° and 84 kPa to 152.2° and 137 kPa, respectively. The superhydrophobic PVDF-PTFE nanofibrous membrane was then tested for desalination by vacuum membrane distillation (VMD), a stable flux of 18.5 kg/m2 h and salt rejection higher than 99.9% was presented throughout the entire testing period of 15 h, 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.