Sustainable Solar Evaporation from Solute Surface via Energy Downconversion.

Solar-powered interfacial evaporation, a cost-effective and ecofriendly way to obtain freshwater from contaminated water, provides a promising path to ease the global water crisis. However, solute accumulation has severely impacted efficient light-to-heat-to-vapor generation in conventional solar evaporators. Here, it is demonstrated that an interfacial solar thermal photo-vapor generator is an efficient light-to-heat photo-vapor generator that can evaporate water stably in the presence of solute accumulation. An energy downconversion strategy which shifts sunlight energy from visible-near infrared to mid infrared-far infrared bands turns water from transparent to its own absorber, thus changing the fixed evaporation surface (black absorber) in a traditional solar evaporator to a dynamic front (solute surface). Light reflected from the solute can be recycled to drive evaporation. The prototype evaporator can evaporate at a high speed of 1.94 kg m h during a persistent solute accumulation process for 32 h. Such an ability to produce purified water while recycle valuable heavy metals from waste water containing heavy metal ions can inspire more advanced solar-driven water treatment devices.