Dual nanofiber membrane with asymmetric wettability for high-performance solar evaporator in zero liquid discharge system

Abstract

The escalating global water scarcity and the environmental burden posed by high-salinity wastewater from reverse osmosis desalination highlight the urgent need for sustainable zero liquid discharge (ZLD) technologies. This study aims to solidify wastewater into sludge via solar evaporation and presents a novel approach to enhancing evaporation efficiency by fabricating a dual nanofiber membrane (DNM) through the co-electrospinning hydrophilic cellulose acetate (CA) and hydrophobic poly(vinylidene fluoride) (PVDF). This unique structure enabled efficient water compartmentalization in the membrane, allowing the evaporator to maintain its maximum evaporation rate by increasing the water-air interfacial area and enhancing vapor escape efficiency. Furthermore, this process imparted asymmetric wettability to the membrane while minimizing heat loss. Although the rapid evaporation rate inevitably led to increased latent heat loss, the overall heat dissipation was remarkably minimized compared to hydrophilic membranes, confirming a high solar energy efficiency of 90.1 %. The optimized DNM, fabricated with a CA/PVDF ratio of 2:3 wt%, achieved a maximum evaporation rate of 2.24 kg/m2h under 1 sun (1 kW/m2), representing a 68 % improvement over hydrophilic CA membranes. The dual nanofiber solar evaporator demonstrated stable long-term performance, validating its potential as a scalable and sustainable platform for solar-driven ZLD applications. © 2026