A nature-inspired suspended solar evaporator for water desalination of high-salinity brines

Abstract

• A water strider-inspired suspended solar evaporator (WSUSE) is fabricated. • The WSUSE shows stable suspending depth regardless of changed salinity. • Salt-resistance is achieved by confining a thin water film on the solar absorber. • High solar evaporation performance is realized even for concentrated brines. As an environmental-friendly and cost-effective technology, interfacial evaporation mediated by photo-thermal materials has shown great potential in solar desalination and wastewater treatment. However, salt accumulation or fouling on the surface of solar absorbers during water evaporation, especially in high-salinity brines, is seemingly inevitable for current solar evaporators, resulting in severely weakened steam generation performance as well as limited long-term use. Here, inspired by water strider, we demonstrate a new type of solar evaporator consisting of a hydrophobic frame, a hydrophilic solar absorber and a heat-insulation layer. Relying on the surface tension force generated by the hydrophobic frame, the solar evaporator can suspend stably just underneath water surface, enabling the confinement of a thin water film on solar absorber for salt-resistance and efficient energy utilization. More notably, the suspending depth is kept almost unchanged in different-salinity brines, achieving high evaporation rates (1.45 kg m -2 h - 1 and 1.35 kg m -2 h - 1 ) in highly concentrated salt solutions (15 wt% and 20 wt% NaCl) under one-sun illumination. No salt-accumulation is observed during the evaporation process till the limit of salt-saturation, and stable evaporation performance is achieved under dynamic water environment. With the merits of antifouling and excellent evaporation performances, the new concept of “suspended evaporators” provides great opportunities in solar-based water desalination and treatment, especially for high-salinity seawater or in closed-systems.