Salt-Accelerated Solar Evaporation in Cationic Aerogels: The Interplay of the Hofmeister Effect and Vertical Channels

Solar-driven interfacial evaporation (SIE) offers a sustainable route for seawater desalination and wastewater purification, but salt fouling still limits its practical application in high-salinity environments. In this study, a cationic polyvinyl alcohol/acryloyloxyethyl trimethylammonium chloride (PVA/AETAC) aerogel (PAA) is developed through ice-templating and freeze-drying for salt-resistant and salt-accelerated solar evaporation. The optimized PAA aerogel achieves an evaporation rate of 3.18 kg m-2 h-1 in 10 wt % NaCl solution under 1.0 sun, exceeding that in pure water, and maintains stable evaporation in 3.5-20 wt % NaCl solutions. During continuous evaporation in 20 wt % NaCl solution, no obvious salt crystallization occurs over 12 h, demonstrating excellent salt resistance. Further structural and mechanistic investigations reveal that the excellent evaporation performance is associated with the interplay of vertically aligned porous channels and a Hofmeister effect mediated water-state redistribution. The vertically aligned porous channels provide continuous pathways for capillary-driven water transport and vapor release, while the AETAC-containing cationic network regulates the local hydration environment within the aerogel. The interaction between quaternary ammonium groups and Cl- increases the proportion of intermediate water and reduces the energy requirement for water evaporation, enabling accelerated evaporation in saline water. This work provides a feasible strategy for designing efficient solar evaporators via vertical water channel engineering and water-state redistribution.