Surface Modification of Electrospun Poly(vinylidene fluoride) Membrane by Low-Pressure Plasma Polymerization to Improve Long-Term Membrane Performance in Water Desalination Process Based on Air Gap Membrane Distillation Method

Today, the lack of access to fresh water has become a serious problem for people around the world. Finding an appropriate method to solve this problem has attracted the attention of many researchers. In recent years, the well-known electrospinning technique has been used as a conventional method to prepare nanofibrous membranes.

A hydrophobic and oleophobic (omniphobic) nanofibrous membrane made of poly(vinylidene fluoride) (PVDF) was prepared by electrospinning. The surface of the nanofibrous membrane was modified using low-pressure plasma polymerization. First, the membrane surface was activated using argon gas plasma to generate free radicals on the polymer chain. Then, perfluorodecyl acrylate monomer was polymerized on the surface of nanofibers in a low-pressure plasma medium. The long-term performance of the prepared omniphobic nanofibrous membrane was evaluated in an air gap membrane distillation (AGMD) module. For this purpose, a saline solution (3.5% by wt) containing 0.2 mM of sodium dodecyl sulfate was used as the feed solution.

To prove the membrane omniphobic characteristic, the contact angle for isopropanol, engine oil, kerosene and water droplets was measured as 120°, 126°, 127°, 140°, respectively. In the AGMD module, the unmodified membrane became wet and unusable after 25 min, whereas the modified membrane maintained a flux of 4.2 L/ (m2.h) and salt rejection of 98% for a time period as long as 300 min. To be more precise, in comparison to the unmodified membrane, the long-term performance and wetting resistance of the modified membrane enhanced more than 12 times. In this research, an efficient and relatively simple technique was provided to modify the surface of electrospun PVDF fibers by low-pressure plasma polymerization of perfluorodecyl acrylate monomer. The modified membrane can be considered for water desalination using AGMD technique.