Facile preparation of omniphobic PDTS-ZnO-PVDF membrane with excellent anti-wetting property in direct contact membrane distillation (DCMD)

Abstract

Membrane distillation (MD) is a promising hybrid thermal/membrane desalination process to treat high salinity industrial wastewater with near-complete rejection of nonvolatile solutes. However, MD membrane still suffers the membrane wetting, which largely affects the desalination performance. In this study, a facile method includes one-step in-situ growth of ZnO nanorods and dip coating of low surface energy 1H,1H,2H,2H-perfluorodecytriethoxysilane (PDTS) was applied to fabricate omniphobic membrane (FZnO-PVDF) with excellent anti-wetting performance. The anti-wetting performance of FZnO-PVDF membrane was systemically evaluated by treating pure water, feed with surfactant and sparingly soluble salts for the first time. Theoretical analysis such as numerical simulation, dynamic liquid entry pressure (LEP) changes and nucleation condition was carried out to explain its anti-wetting mechanism. Results showed that FZnO-PVDF membrane displayed high contact angles towards water droplets with (∼121.1°) or without alcohol (∼164.9°), and low sliding angle for water (10.6°). The resultant membrane not only exhibited excellent resistance for surfactant-induced membrane wetting towards 0.6 mM sodium dodecyl sulfate (SDS) due to its enhanced LEP value (225 kPa), but also remarkable resistance for scaling-induced membrane wetting because of the high energy barrier for CaSO4 heterogeneous nucleation (34.2 mJ mol−1) and slip boundary condition of membrane. This study provides valuable insights for fabricating omniphobic membrane and comprehending its anti-wetting property in MD application.