Designing triple-layer superhydrophobic/hydrophobic/hydrophilic nanofibrous membrane via electrohydrodynamic technique for enhanced anti-fouling and anti-wetting in wastewater treatment by membrane distillation

Developing high-performance membranes for membrane distillation (MD) to treat highly saline industrial wastewater is of great significance. In this work, a superhydrophobic/hydrophobic/hydrophilic triple-layer membrane combining an electrosprayed superhydrophobic top layer, an electrospun hydrophobic nanofibrous intermediate layer and a hydrophilic microporous membrane substrate was fabricated by using electrohydrodynamic techniques. The top superhydrophobic surface possesses a unique surface morphology composing of hydrophobic SiO₂-polymer microbeads with nanoscaled protrusions and interconnected thin nanofibers, which contributed to the enhanced water flux for desalination in direct contact MD. By tuning the concentrations of hydrophobic SiO₂ nanoparticles and polyvinylidene fluoride-co-hexafluoropropylene for electrospraying the top layer, the triple-layer membrane showed both enhanced anti-fouling and anti-wetting properties due to the reduced liquid-solid contact area and stable Cassie-Baxter state. The triple-layer membrane exhibited stable MD performances when using real seawater and industrial flue gas desulfurization wastewater as the feed solutions, while no obvious fouling and wetting being observed even at 60% water recovery. This study provides an effective approach for fabricating a high-performance triple-layer superhydrophobic/hydrophobic/hydrophilic membrane for potential practical MD applications for industrial wastewater treatment.