Facile fabrication of omniphobic PVDF composite membrane via a waterborne coating for anti-wetting and anti-fouling membrane distillation

Omniphobic membranes have been brought to great attention recently regarding the ability to resist both water and low surface tension liquids, thus can be utilized for desalination of saline wastewater containing low surface tension contaminants in membrane distillation (MD). In this study, a facile, environment-friendly, and one-step strategy is developed for fabricating an omniphobic membrane with re-entrant structure and low surface energy by spraying a waterborne coating solution comprising of fluorocarbon surfactant (FS, Zonyl@8867L), fluorinated alkyl silane (FAS), and silicon dioxide nano-particles (SiO 2 NPs) onto amino functionalized polyvinylidene difluoride (PVDF) membrane via electrostatic adsorption. As a result, the prepared omniphobic FS/FAS/Si membrane possesses high liquid repellency to water, diiodomethane, mineral oil-in-water emulsion (0.10 % v/v), mineral oil, and SDS solution (0.40 mM) with the contact angle of 164.40 ± 0.95°, 159.12 ± 3.12°, 154.31 ± 3.71°, 153.31 ± 2.09°, and 157.14 ± 3.29°, respectively. Compared to the original PVDF membrane, the omniphobic FS/FAS/Si membrane displays higher rejection (about 99.99%) and superior anti-wetting and anti-fouling characteristics even to the saline feed solution with surfactants, oil pollutants, or hydrophilic organic pollutants in MD process. The results mentioned above verify that the obtained omniphobic FS/FAS/Si membrane has potential application for the desalination of the high saline wastewater containing low surface tension contaminants.