An Extremely Salt-Resistant Hydrogel-Based Solar Evaporator for Stable Saturated Brine Desalination

Hydrogel-based solar evaporators are widely concerned because of their excellent evaporation performance due to the "water activation" effect by reducing the evaporation enthalpy. However, the current challenge is the trade-off between a high evaporation rate and salt tolerance. Here, a 3D chitosan-based hydrogel evaporator with a directional vertical channel structure using a one-pot in situ strategy and directional freezing method, is innovatively designed. Owing to its vertical channel structure, salt ions can quickly return, while steam can overflow without obstruction, allowing the evaporator to achieve a high evaporation rate and exceptional salt resistance, simultaneously. Consequently, an extremely salt-resistant system is achieved, even in saturated brine (salinity of 26.47 wt.%), with no salt crystals accumulating after continuous over 8 h of evaporation and an excellent evaporation rate of 2.83 kg m^-2 h^-1 under one sun illumination. This is the best reported salt-resistant hydrogel-based evaporation system. With the record-high salt resistance, this work improves the practicality of hydrogel evaporators for high-salinity desalination.