Mimicked microfluidic Janus evaporator for dual functions of solar evaporation and fog collection

Solar evaporation for water purification potentially achieves abundant freshwater production without CO₂ emission. In the present study, we develop a unique kind of solar evaporators with three-dimensional biomimetic microstructures on its top surface based on a 3D printing technique. Moreover, the different wettability of their top and bottom surfaces enables them to exhibit an amazing Janus effect, achieving the rapid transportation of water from the bottom to the top surface motivated by the Laplace pressure. Additionally, the water will climb up along the surfaces of bionic microstructures on the top surface of the evaporators to enlarge the surface area of the water. Thus, there will be rapid evaporation of water when irradiated by sunlight during the day. It is demonstrated that the evaporation rate of water is 1.97 kg m⁻² h⁻¹ with a light intensity of one sun, and the photothermal conversion efficiency is larger than 92 %. In addition, the evaporation rate is still as high as 1.74 kg m⁻² h⁻¹ for seawater with an average salt concentration of 3.5 wt%. Most significantly, the fog collection rate of such an evaporator with bionic microstructures can be as high as 41.45 kg m⁻² h⁻¹ at a humidity of 99 % RH at night. The dual functions of our bionic evaporators enable amazing self-cleaning performance with fog collection to wash the crystalline salt and any other wastes off the top surface of the evaporators, promising bionic evaporators for long-lasting solar evaporation of seawater and wastewater.