SUPERHYDROPHOBIC NANOCOMPOSITE MEMBRANE FABRICATION WITH HYBRIDIZED ELECTROSPINNING AND ELECTROSPRAYING TECHNOLOGY FOR MEMBRANE DISTILLATION APPLICATION

Abstract

Membrane distillation (MD) is an emerging membrane separation process that is now becoming competitive with other desalination techniques. Generally, MD membranes are fabricated with “polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or Poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP)” due to their superior anti-wetting property and mechanical strength. In this work, successful attempts were made to fabricate a hydrophobic nanofibrous membrane with polystyrene (PS) blended with a relatively small fraction of PVDF to maintain the mechanical strength of the overall composite MD membrane. PS is nearly 80-95% cheaper than PVDF with highly porous morphology and thermal resistance. The membranes were optimized by various characterization methods like contact angle (CA), surface energy, porosity, liquid entry pressure (LEP), field emission scanning electron microscopy (FE-SEM), chemical stability, and mechanical strength. The porosity of around 83.38% and contact angle of 144±2° were achieved from the electrospun membrane with “4.25% PVDF and 10.75% PS” polymeric concentration. The optimized membrane was then further chemically modified by grafting the silane functionalized WO3 nanoparticles (NPs) by the novel electrospraying technology. The modified membrane achieved superhydrophobic property, and hydrophobicity was enhanced to superhydrophobic (water contact angle ~170°, porosity ~83%) by incorporating multi-scale re-entrant structure morphology by electrospraying silane functionalized tungsten trioxide (WO3) nanocomposite. Compared to common titanium dioxide or zinc oxide nanoparticles, WO3 is relatively economical and has superior anti-bacterial, anti-fouling properties against organic compounds like dyes. Further, WO3 exhibits superior chemical resistance in a large range of pH (3 to 11) solutions. The membrane performance was tested under direct contact membrane distillation (DCMD) configuration for the anti-wetting test in which the membrane delivered constant flux (above 14 LMH) during the testing without any wetting during the whole run of MD.