Salt-Induced Phase Separation in Polyampholyte Hydrogels for Stable Solar Desalination

Solar-driven interfacial evaporation technology represents a promising decentralized freshwater supply solution that can effectively alleviate global freshwater scarcity. However, the evaporation rate of conventional hydrogel evaporators is often limited by poor pore connectivity and salt-induced structural shrinkage. Inspired by the salting-out and salting-in behaviors of polymers, we fabricated a polyampholyte hydrogel through high-concentration sodium sulfate, which induces a salting-out effect to form an interconnected porous structure in the hydrogel. This hydrogel not only exhibits efficient transport channels in pure water but also demonstrates salting-in characteristics in seawater environments, effectively resisting salt-induced shrinkage. After functionalization with polypyrrole photothermal nanoparticles, the resulting evaporator achieved a high evaporation rate of approximately 2.18 kg·m^-2·h^-1 under 1.0 kW·m^-2 irradiation in real seawater and maintained stable performance without decay over seven days of continuous operation. This study provides a scalable and environmentally friendly design strategy for high-performance hydrogels in sustainable solar desalination.