Architecting asymmetrical Janus membrane for robust membrane distillation desalination with enhanced anti-fouling...

Membrane fouling and wetting represent critical impediments to the broader application of membrane distillation (MD). To address these challenges, this study engineered an omniphobic membrane and an asymmetrical Janus membrane, both constructed on a polyvinylididene fluoride (PVDF) substrate, and systematically evaluated their performance in MD under challenging conditions. Results demonstrated that the Janus membrane exhibited significantly more stable flux (declining from 9.8 to 9.2 L·m⁻²·h⁻¹) compared to the omniphobic membrane (decreasing from 12.7 to 7.5 L·m⁻²·h⁻¹) when treating oil-containing wastewater. This enhancement is attributed to the formation of a durable hydration layer via chitosan-water molecular interactions, which substantially improves wetting resistance of Janus membrane against low-surface-tension liquids. Theoretical analyses based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory further confirmed that the silica nanoparticle overlay significantly enhances the membrane's anti-wetting properties. In direct contact MD experiments using real shale gas produced water (SGPW), the Janus membrane maintained stable desalination performance over 12 h, with only a 10.5 % flux attenuation compared to a 20.3 % decline observed in the omniphobic control, while retaining high salt rejection. These findings underscore the robust application potential of Janus membranes in the desalination of complex industrial wastewaters containing diverse low surface-tension contaminants.