Development of a Novel Dual-Layer Janus Membrane via NIPS Process for Sweep Gas Membrane Distillation (SGMD) and Its Orientation-Dependent Response

Dual-layer membranes can offer significant advantages in desalination via membrane distillation (MD) compared to conventional single-layer designs. In this study, we report the development of a novel dual-layer nylon/polyvinylidene fluoride (PVDF) membrane with a Janus architecture, specifically engineered for application in sweeping gas membrane distillation (SGMD). The non-solvent induced phase separation (NIPS) method was used to cast PVDF solution on the top of a commercial nylon membrane. Water contact angle (WCA) measurements showed asymmetrical wettability. Scanning electron microscopy (SEM) confirmed that the PVDF layer was firmly anchored to the nylon support without signs of delamination. Desalination experiments were conducted using SGMD, where a significant flux enhancement as high as 81.2% was observed when the feed solution contacted the hydrophilic nylon surface while the hydrophobic PVDF surface faced the permeate side with gas flow. This enhancement was attributed to the high partitioning coefficient of the liquid–vapor mixture on the hydrophilic feed surface and the rapid vapor release across the hydrophobic permeate surface. Overall, these results demonstrate that hydrophilic membranes with small pore sizes (i.e., 0.22 µm) can serve effectively as supports when fabricated using the NIPS process, enabling new configurations for high-performance SGMD.