Siphoning and Hofmeister Effects-Enhanced Hanging Inverted Cone Evaporator with Top-Down Water Supply for Efficient Solar-Thermal Seawater Desalination

Although solar-driven water evaporation is promising for mitigating water scarcity in the areas lacking clean water and far away from power grids and water grids, the low solar energy utilization, high water vaporization enthalpy, and salt deposition seriously impede its practical application for continuous, efficient, and stable desalination of seawater. Herein, siphoning and Hofmeister effects-enhanced hanging inverted cone-shaped solar-thermal evaporator with a top-down water supply is designed for efficient solar-thermal desalination of seawater, which is prepared by in situ polymerization of pyrrole on nonwoven cellulose fabrics and subsequent coating with poly(vinyl alcohol) (PVA) hydrogel. The 3D hanging inverted cone structure significantly enlarges the areas for solar-thermal energy conversion and water evaporation, while the top-down water supply via the pressure of the siphoning effect ensures sufficient water, achieving a high water evaporation rate of 3.90 kg m^-2 h^-1 with the water vaporization enthalpy of 2.06 kJ g^-1 during solar-thermal evaporation of pure water under 1-sun irradiation. In an aqueous solution with 3.5 wt % NaCl, the PVA hydrogel generates additional intermediate water via the Hofmeister effect to further reduce the water vaporization enthalpy to 1.61 kJ g^-1, thereby increasing the water evaporation rate to 4.89 kg m^-2 h^-1. Thanks to the significantly enlarged evaporation surface area, the reduced water vaporization enthalpy, and the sufficient top-down water supply, the hanging inverted cone-shaped evaporator with the top-down water supply is highly efficient in continuous desalination of natural seawater, achieving a water evaporation rate of 4.64 kg m^-2 h^-1 with a salt rejection of 99.99%.