Natural-inspired hierarchic double-Janus solar evaporator for stable clean water production from high-salinity emulsions

Interfacial solar evaporation shows great potential in clean water production, emulsions separation, and high-salinity brine treatment. However, it remains challenging for the evaporators to maintain a high evaporation rate in the high-salinity emulsions due to the co-pollution of salt and oil. Herein, we first proposed a hierarchic double-Janus solar evaporator (HDJE) with a hydrophobic salt-rejecting top layer and oil-rejecting bottom layer. Compared to the traditional one, HDJE could treat industrial high-salinity oil-in-water emulsions stably for over 70 h, with a stable average evaporation rate of 1.73 kg m-2 h-1 and a high purification efficiency of up to 99.8% for oil and ions. It was also verified that HDJE could be used for high-efficiency purification of oily concentrated seawater outdoor. An average water production rate of 3.59 kg m-2 d-1 and a TOC removal ratio of over 98% was obtained. In conclusion, this study provides a novel way to effectively dispose of high-salinity oily wastewater. Interfacial solar evaporation technology could greatly alleviate global water scarcity with little climate change and affordable energy. Hierarchic double-Janus solar evaporator (HDJE) has both salt and oil-rejecting functions. Through reasonable vertical grading design, HDJE enables stable evaporation and purification of industrial high-salinity oil-in-water emulsions in practical conditions. In addition to high-salinity emulsion, other actual oily wastewater also contains salts. Therefore, this work also provides a new strategy for the anti-pollution design of interfacial solar evaporators. The hierarchic double-Janus structure endows the evaporators potentially applicable in clean water production, wastewater treatment, and zero liquid discharge.