Salt ion triggered hydration chemistry for salt-rejecting solar-driven water evaporation

Abstract

The escalating global freshwater scarcity necessitates sustainable and efficient desalination technologies, yet conventional methods remain constrained by high energy consumption and operational complexity. Solar-driven water evaporation has emerged as a promising alternative, but its practical deployment is hindered by salt fouling, which restricts the evaporation efficiency and durability under high-salinity conditions. This review highlights salt ion triggered hydration chemistry as pivotal for hydrogel-based evaporators, with a focus on two strategies: Hofmeister effect driven hydration and anti-polyelectrolyte effect enabled hydration. These two approaches have demonstrated remarkable potential in overcoming the limitations of conventional desalination methods, such as high energy consumption and salt fouling through tailoring water transport pathways and enhancing salt tolerance. The key mechanism for salt rejection is that these polymers can bind with salt ions to suppress salt precipitation, release more weakly bound water to reduce the evaporation enthalpy and improve the brine pumping ability of evaporators in saline water. Hydration chemistry has thus emerged as a cornerstone for the design of next-generation hydrogel evaporators, advancing water purification, which aligns with global sustainability goals. We believe this review will bring new understanding into the chemical design of hydrogel based solar-driven evaporation systems.