Engineering superhydrophobic surface on poly(vinylidene fluoride) nanofiber membranes for direct contact membrane distillation

The characterizations reveal that the modifications have altered the membrane surface morphology and topology and made the membrane superhydrophobic due to their hierarchical structures. Compared with unmodified membrane, the integrally-modified membrane (I-PVDF) can achieve a high and stable MD water flux of 31.6 L m−2 h−1 using a 3.5 wt% NaCl as the feed solution while the feed and permeate temperatures were fixed at 333 K and 293 K, respectively. To the best of our knowledge, this result is superior to all other PVDF flat-sheet membranes tested under the same or similar conditions, which is believed to be attributed to the open-surface pore structure and thin thickness of the PVDF nanofiber membrane with the aid of electro-spinning. The superhydrophobic nature of the membrane surface brought by the integral modification on all nanofibers renders the membrane anti-wetting property while remaining high water flux.