Omniphobic Polyvinylidene Fluoride Membrane Decorated with a ZnO Nano Sea Urchin Structure: Performance Against Surfactant-Wetting in Membrane Distillation

Membrane distillation, an emerging desalination technology, shows much promise for treating industrial wastewater with high salinity. One major challenge that impedes its implementation for industrial applications is the wetting of hydrophobic membranes such as polyvinylidene fluoride (PVDF), resulting in a sharp decline in salt rejection. Wetting occurs when the feed solution contains surfactants, such as sodium dodecyl sulfate (SDS). It has been demonstrated that growing rough structures on the membrane surface followed by fluorination helps the membrane maintain its hydrophobicity. In this study, an omniphobic membrane was successfully prepared by first growing a layer of dense nano-ZnO needles on the surface of a pristine PVDF membrane, followed by a typical fluorination treatment. The modified membrane, with its surface similar to a nano sea urchin in appearance, exhibited a superior antiwetting property, having a high contact angle about 160° against a 50 g/L NaCl solution containing 0.3 mM SDS. The modified membrane showed a fairly good wetting resistance against 0.3 mM SDS, having a nearly 100% salt rejection in treating 50 g/L NaCl, whereas the pristine PVDF membrane could be easily wetted. The modified PVDF membrane shows promise in treating high-salinity wastewaters containing surface-active substances.