Cellulose acetate-based dual-layer nanofibrous composite membranes for desalination by membrane distillation

Desalination has emerged as a key solution to the growing global demand for clean water. Membrane distillation (MD) has gained increasing attention due to its ability to treat hypersaline and complex wastewater using low-grade thermal energy. However, MD membranes continue to face performance challenges, particularly low permeate flux and limited resistance to pore wetting. This study presents the fabrication of electrospun dual-layer (DL) nanofibrous membranes, utilizing a hydrophobic polymer blend of polyethersulfone (PES) and polyvinylidene fluoride-co-hexafluoropropylene (PcH) as the feed layer, and hydrophilic cellulose acetate (CA) as the permeate layer. The thickness of each layer was precisely adjusted by varying the electrospun volume ratio of each polymeric solution, while maintaining a constant total volume. Structural and surface characterizations were conducted using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), water contact angle (WCA), and measurements of membrane thickness, porosity, surface roughness, and liquid entry pressure (LEP). The membranes' performance was evaluated using a direct contact membrane distillation (DCMD) setup under varying feed salt concentrations and flow rates. Among the tested configurations, the DL membrane with the thinnest CA layer exhibited the highest permeate flux, attributed to reduced overall thickness, increased porosity, and minimized vapor-liquid interface distance, while maintaining high salt rejection (>99.9 %). The developed DL membrane demonstrated superior desalination performance and, by combining hydrophobic and hydrophilic polymers, offers a promising and viable alternative to conventional single-layer membranes based solely on hydrophobic materials for efficient and robust MD desalination.