A Janus evaporator with low tortuosity for long-term solar desalination

Abstract

The emerging interfacial solar steam generation technology with high solar-to-vapor conversion efficiency shows great potential in the field of solar desalination, while salt accumulation issues arising from localized solar-heating and water evaporation significantly threaten the stability of the system. Herein, we report the performance of a Janus evaporator based on a SiO₂/cellulose nanofiber/carbon nanotube hybrid network with a low tortuosity pore structure for long-term seawater desalination. The asymmetric wettability enables the evaporator to float on water with the hydrophobic layer out of the water for better heat localization and the hydrophilic layer in the water for continuous water pumping, while the low tortuosity pore structure endows the evaporator with excellent salt excretion capability. Continuous solar desalination tests (100 hour) show that the Janus evaporator demonstrates stable steam generation with over 80% efficiency in 3.5 wt% NaCl solution (average salinity of seawater) under 1 sun. Moreover, tolerance tests illustrate that the evaporator can withstand a salt concentration of up to 12 wt% without salt deposition, suggesting great potential of the use of the Janus evaporator in industrial water treatment with a salinity far beyond that of seawater, such as the saline waters produced from oil and gas extraction.