Solar-thermo-radiative evaporator for continuous steam generation and salt harvesting

Solar-driven interfacial evaporation attracts great attention in desalination and wastewater treatment. However, the gradual decline of evaporation rate caused by salt accumulation restricts its long-term operation. Here, we developed a new solar-thermo-radiative evaporator that uses infrared photons as heating source to promote the interfacial evaporation with edge-preferential crystallization and gravity-assisted salt harvesting. The solar absorber exhibits broadband light-harvesting and converts the sunlight into mid-infrared radiation, localizing the radiative heat at the neighboring water-film for directly phase-change evaporation. Benefiting from the self-manipulated salt water transport, this evaporator spatially isolates the crystallized salts from the evaporative surface, achieving an evaporation rate (0.71 kg∙m−2∙h−1) with high steam temperature (＞80 °C) under 1 sun. As the salt is continuously expelled at the edge of the evaporator, the salt-harvesting performance (36.25 g∙m−2∙h−1) is achieved during 40 h of non-stop solar desalination without affecting water evaporation. Such non-contact design thus circumvents the salt-blocking and/or contamination issue on the solar absorber, making it uniquely suitable for applications in desalination or water purification, with an added benefit of resources recovery.