Plasma-Induced Superhydrophobicity as a Green Technology for Enhanced Air-Gap Membrane Distillation

Superhydrophobicity has only recently become a requirement in membrane fabrication and modification. Superhydrophobic membranes have shown improved flux performance, fouling and scaling resistance in long-term membrane distillation (MD) operations compared to simply hydrophobic membranes. Here, we introduce plasma micro-nanotexturing followed by plasma deposition as a novel, dry and green method for superhydrophobic membrane fabrication. Using plasma micro-nanotexturing, commercial membranes (WSCA from 40-135 °) are transformed to superhydrophobic (WSCA>150 °, hysteresis <10 °). To this direction, hydrophobic Polytetrafluoroethylene (PTFE) as well as hydrophilic Cellulose acetate (CA) membranes are transformed to superhydrophobic. The superhydrophobic PTFE membranes showed enhanced water flux in standard air gap membrane distillation and more stable performance compared to the commercial ones for at least 48 h continuous operation, with salt rejection >99.99%. Additionally, their performance and high salt rejection remained stable, when a low surface tension solution containing SDS/NaCl (55 mN/m) was used, show-casing their anti-wetting properties. The improved performance is attributed to superhydrophobicity and increased pore size after plasma micro-nanotexturing. More importantly, CA membranes, which are initially unsuitable for MD (WSCA≈40 °), showed excellent performance with stable flux and salt rejection >99.2% again for at least 48 hours, demonstrating the effectiveness of the proposed method for wetting control in membranes regardless of their initial wetting properties.