Polydopamine-Enabled Photothermal and Interfacial Reinforcement of Sand-Integrated Organohydrogels for Solar Evaporation and Sand Fixation

Water scarcity and land desertification are interconnected global challenges requiring materials that simultaneously enable freshwater production and sand stabilization. Herein, we develop a gelation-directed hierarchical particle-reinforced (HPR) organohydrogel by integrating polydopamine (PDA)-decorated sand particles into a poly(vinyl alcohol) (PVA) network. The PDA layer provides broadband photothermal conversion while strengthening the sand-PVA interface, facilitating interfacial stress transfer, whereas the sand particles reinforce the polymer network and stabilize the granular framework. Meanwhile, the hydrated PVA network regulates confined water and lowers its evaporation enthalpy by 20.6–24.3%, while the hierarchical architecture preserves interconnected pathways for water and ion transport. The optimized HPR organohydrogel achieves an evaporation rate of 2.12 kg m–2 h–1 and an apparent efficiency of 94.3% under one-sun irradiation, with stable performance under repeated cycling, high salinity, extreme acidic/alkaline, and oil-contaminated conditions. Notably, evaporation-induced salt enrichment triggers Hofmeister interactions that further strengthen the hydrogel-sand framework, establishing positive feedback between solar evaporation and sand stabilization. This gelation-directed interfacial reinforcement strategy transforms hydrogel formation into a functional assembly process, exploring the potential for coupling solar-driven freshwater generation with ecological sand stabilization.