Engineering self-cleaning and robust microporous hydrophobic membranes through nanoparticle-enhanced composite spray coating for membrane distillation

Water scarcity necessitates advanced desalination technologies. Membrane distillation (MD) is promising but requires highly hydrophobic membranes. However, conventional hydrophobic membranes are prone to pore wetting during long-term operation, which causes severe salt leakage and flux decline, critically hindering practical applications. This study develops a synchronous composite spray-assisted non-solvent induced phase separation strategy to fabricate superhydrophobic polyvinylidene fluoride (PVDF) membranes, which enables simultaneous phase inversion and surface functionalization. Fluorinated silica nanoparticles (F-SiO₂) were synthesized and integrated into the non-solvent spray for membrane preparation. The membrane (PVDF-S1.5) prepared with non-solvent spray containing 1.5 wt% F-SiO₂ exhibited superhydrophobicity with a water contact angle (WCA) of 150.75 ± 2.46° and a liquid entry pressure (LEP) of 2.50 ± 0.02 bar. The embedded nanoparticles and the hierarchical structure ensured robust hydrophobicity, showing steady hydrophobic property after prolonged immersion in boiling water. During the vacuum MD test using a 60 ℃ 3.5 wt% NaCl feed solution, the membrane achieved a vapor flux of 18.21 ± 0.50 kg·m⁻²·h⁻¹ and a salt rejection > 99.99 %. The PVDF-S1.0 membrane with less F-SiO₂ showed a higher flux of 20.31 ± 0.31 kg·m⁻²·h⁻¹ with a salt rejection > 99.99 %. The membranes demonstrated excellent 50-hour stability and effective performance recovery after cleaning, showing great potential for seawater desalination.