Electrospun nanofibrous omniphobic membrane for anti-surfactant-wetting membrane distillation desalination

A novel omniphobic membrane was fabricated for anti-surfactant-wetting membrane distillation (MD) by electrospinning hybrid nanofibers comprising cellulose acetate (CA) and silica nanoparticles (SiNPs) to create hierarchical re-entrant surface structures, followed by surface fluorination to lower the surface energy of the fibrous membrane. The effects of surface morphology and surface energy on membrane wettability were investigated through evaluating wetting resistance to various liquids with different surface tension, it was demonstrated that both ultralow surface energy and hierarchical re-entrant surface structure were indispensable for membrane wetting resistance to low-surface-tension liquids. Specifically, the secondary re-entrant structure induced by SiNPs inlayed in the cylindrical nanofibers played a critical role in achieving surface omniphobicity. The fabricated omniphobic fibrous membrane exhibited superior anti-wetting properties, as evidenced by the contact angles for water and decane, which were as high as 155.6 ± 3.9° and 95.3 ± 2.5°, respectively. Compared with the hydrophobic membranes, the omniphobic membrane possessed robust wetting resistance to the low-surface-tension feed and maintained stable permeate flux and salt rejection during direct contact MD experiments, while all the tested hydrophobic membranes can be easily wetted. Our results suggest that the fabricated omniphobic membrane is promising and feasible for MD desalinating the wastewaters with low-surface-tension contaminants.