Advanced multi-nozzle electrospun functionalized titanium dioxide/polyvinylidene fluoride-co-hexafluoropropylene (TiO₂/PVDF-HFP) composite membranes for direct contact membrane distillation

The unique capabilities of electrospinning technology are being increasingly utilized in the fabrication of hydrophobic membranes to improve the membrane distillation (MD) process in recent years. In this study, hydrophobic titanium dioxide (TiO₂) nanoparticles functionalized by fluorosilane were incorporated into electrospun membranes using single, coaxial, and dual nozzles to develop novel membrane architectures for improved physico-chemical properties for MD. By incorporating fluorosilane coated TiO₂ into the PVDF-HFP solution during the membrane synthesis and using an advanced multi-nozzle to form various hierarchical membrane structures tuned the size and structure of the nanofibers and made them vastly superior for the application in MD. The single and coaxial nozzle membranes showed contact angles close to 150° and the dual-nozzle membrane assembled bead-on-string fibers achieved superhydrophobicity (i.e., contact angle of 153.4°). To test the functionalized titanium dioxide/polyvinylidene fluoride-co-hexafluoropropylene (TiO₂/PVDF-HFP) composite membranes for MD performance, the membranes were subjected to long-term direct contact MD for about two days to monitor their water vapor flux and selectivity. Compared to commercial PVDF membranes, all electrospun F-TiO₂/ PVDF-HFP membrane achieved higher water vapor flux of 40 L m⁻² h⁻¹ (60 °C feed and 20 °C permeate) with a brine (7.0 wt% NaCl) as the feed solution and also exhibited anti-wetting property while maintaining high water flux compared to the membrane without TiO₂ incorporation.