Enhanced hydrophobicity and AGMD performance of PSF nanocomposite membranes through MWCNT incorporation and silicone surface coating

Air gap membrane distillation (AGMD) requires hydrophobic porous membranes that can minimize wetting while maintaining effective vapor transport, particularly for high-salinity water treatment. However, conventional polymeric membranes and nanocomposite modifications may not simultaneously provide adequate hydrophobicity and desalination performance. In this study, polysulfone (PSF) membranes were fabricated by non-solvent-induced phase separation using DMF at 17 wt% and evaluated for AGMD desalination of 35 g/L NaCl feed water. Six membrane configurations were prepared by incorporating raw graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) at 0.05 wt%, either individually or combined with a commercial silicone-based spray coating as a post-fabrication hydrophobic sealant agent (HSA). Membrane morphology, surface chemistry, topography, wettability, and porosity were characterized using FESEM, FTIR, AFM, water contact angle, and gravimetric measurements. Under identical operating conditions, the MWCNT-containing membrane with HSA coating (S5) achieved the best overall performance, with a water contact angle of 95°, salt rejection of 99%, and permeate flux of 11 L m⁻² h⁻¹. The results show that combining low-loading raw MWCNT incorporation with a simple post-fabrication HSA coating provides an effective surface-engineering strategy to improve membrane hydrophobicity and AGMD desalination performance without chemical functionalization.