ZnO Nanorod Induced Omniphobic Polypropylene Membrane for Improved Antiwetting Performance in Membrane Distillation

Maintaining hydrophobicity of the membrane in membrane distillation is vital for treating high-salinity feedwater containing surface active substances due to their wetting impact on the membrane. An effective approach to mitigate membrane wetting is to build rough nanostructures on a pristine membrane to render its surface omniphobic. Directly building nanostructures on polypropylene (PP), however, is challenging, as the material is chemically inert. In this study, a novel method was developed to physically plant ZnO seeds on the PP membrane above the material’s heat deflection temperature. A biomimetic nanostructure was then constructed on the membrane surface by growing fluorinated ZnO nanorods along the seeded PP substrate. The resulting omniphobic membrane exhibited a contact angle constantly above 160° against a test solution containing 50 g/L NaCl and 0.06 mM sodium dodecyl benzenesulfonate. Compared to the pristine PP membrane, the modified PP membrane showed a nearly complete salt rejection and much improved antiwetting capacity against the surfactant added in the test solution. The physical seeding method presented in this study is therefore a promising alternative approach to functionalize chemically inert polymeric substrates with constructed biomimetic nanostructures.