Superhydrophobic dual layer functionalized titanium dioxide/polyvinylidene fluoride-co-hexafluoropropylene (TiO2/PH) nanofibrous membrane for high flux membrane distillation

In this study, superhydrophobic dual layer membranes with highly porous structure were fabricated using electrospinning and electrospraying techniques. Electrospinning method was used to produce the support nanofibrous layer using polyvinylidene fluoride-co-hexafluoropropylene (PH) as the polymer and a mixed solvent system of N,N-Dimetylformamide (DMF) and acetone. Afterwards, hydrophobic, functionalized TiO2 nanoparticles were deposited on the surface of the support layer using the electrospraying technique. TiO2 chemical functionalization and their deposition on the support layer were investigated by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy. The effects of different concentrations of TiO2 nanoparticles (100 and 200wt%) and PH (7–9wt%) in the electrospraying solution on the dual layer membrane characteristics, such as surface morphology, pore size, porosity, water contact and sliding angle, mechanical properties, and liquid entry pressure (LEP) were thoroughly examined. The results show that porous superhydrophobic nanofibrous membranes with water contact angles higher than 150°, sliding angles lower than 10°, and low contact angle hysteresis were successfully fabricated. Consequently, the prepared membranes showed comparable LEP with the commercial polyvinylidene fluoride (PVDF) membrane, but at much higher porosity (>85%) and mean pore size (>0.70μm). Performance of the dual layer membranes, along with the single layer PH and commercial PVDF membranes, were carried out in a direct contact membrane distillation setup. The superhydrophobic nanofibrous membrane showed noticeably more stable operation compared with the neat PH membrane and consistently higher flux (38.71∓1.105Lm−2h−1) than the commercial PVDF membrane (26.64∓0.97Lm−2h−1) during 24h of operation.