Temperature-Sensitive Porous Hydrogel with High Salt Resistance for Solar Interface Evaporators

Solar interfacial evaporation is a promising water desalination method. However, developing cost-effective solar evaporators with a high salt resistance remains a challenge. One of the main methods to ensure an adequate water supply to the evaporation surface in solar interfacial evaporation involves maintaining a sufficient water supply to the surface. However, the water transport capacity positively correlates with heat loss, creating a trade-off between thermal localization and salt resistance. This work introduces an innovative approach utilizing poly(N,N-diethylacrylamide) (PDEAAm) and sodium alginate as the hydrogel matrix, combined with sodium dodecyl sulfonate and mechanical stirring to fabricate a macroporous structure. This structure facilitates the autonomous generation of a Janus-structured macroporous hydrogel evaporator, which mitigates the trade-off to achieve optimal salt-resistance and is applicable for solar interfacial evaporation of concentrated saline. The evaporation and salt resistance performance of this evaporator was evaluated, revealing that PY-DGSP exhibits exceptional evaporation and salt resistance capabilities. The thermosensitive properties of PDEAAm enable PY-DGSP to self-respond under illumination, forming a hydrophobic upper layer and a hydrophilic lower layer Janus structure. At night, the structure reverts to a hydrophilic state, achieving thermal localization during evaporation. Furthermore, the macroporous structure significantly enhances the hydrogel's water transport capacity and salt diffusion. With these characteristics, the evaporator demonstrated the absence of salt crystallization after 10 h of exposure to 1 sun illumination in 10% saline, maintaining a stable evaporation rate of 2.11 kg·m–2 h–1. This study presents a method for achieving efficient solar interfacial evaporation based on a self-responsive Janus macroporous hydrogel.