Conical chitosan/polyvinyl alcohol aerogel evaporator with multiscale water activation and directional salt management for efficient solar desalination

Solar-driven interfacial evaporation offers a sustainable route for off-grid water purification, but achieving high evaporation efficiency and salt resistance remains a core design challenge. Herein, we propose a cross-scale integration strategy that simultaneously reduces evaporation enthalpy and enhances salt resistance. A 3D conical chitosan/polyvinyl alcohol (CSPx) aerogel-based evaporator with vertically oriented hierarchical micro-nano channels was prepared by unidirectional freezing, where polyvinyl alcohol incorporation enabled the formation of nanopores, enhanced porosity, and high-proportioned intermediate water. The optimized CSP2 achieves an evaporation rate of 2.39 kg m −2 h −1 and a solar efficiency of 100.4% under one solar intensity. For the first time, a fully coupled thermal–fluid–mass transfer COMSOL simulation revealed the surface temperature and evaporation flux distributions, clarifying the heat balance and confirming that interfacial cooling and environmental heat harvesting enable the conical structure to exceed 100% efficiency. The evaporator enables directional salt crystallization at the cone apex in 5 wt% NaCl solution and exhibits strong antibacterial activity, excellent purification performance for seawater, heavy-metal wastewater, and dye-contaminated water, as well as outstanding potential for practical applications. To sum up, this research provides insights into the performance optimization of solar evaporators and highlights the potential applications in alleviating the global freshwater crisis.