Biomimetic Salt-Excreting 2D Evaporator Enables Spatially Decoupled Evaporation, Salt Harvesting, and Energy Recovery for Sustainable Brine Treatment

Abstract

Sustainable valorization of hypersaline brines through solar evaporation constitutes a critical frontier in the global water-energy-resource nexus, yet it is constrained by the tight coupling among evaporation, salt crystallization, and thermal management. Herein, we report a mangrove-inspired 2D poly(vinyl alcohol)/poly(ionic liquid) (PIL) hydrogel (PVIL) evaporator integrated with a thermoelectric generator (TEG) that achieves spatial decoupling: vapor generation at the top, continuous salt harvesting at lateral edges, and energy recovery at the bottom. Mechanistically, fixed cationic imidazolium groups in the PIL network induce Donnan exclusion that suppresses ion accumulation near the evaporation interface, while a unidirectional water supply promotes edge-directed lateral transport of concentrated brine, leading to preferential salt crystallization at the edges. This unique "repel-and-transport" architecture enables continuous operation in 10 wt% NaCl for over 5 months, achieving a cumulative brine processing of 8.2 t m⁻² while harvesting 0.86 t m⁻² of solid salt. Meanwhile, a latent heat-assisted cooling strategy at the TEG cold side enables a favorable evaporation–electricity trade-off, incurring only ~7% evaporation penalty relative to the PVIL evaporator without TEG, while delivering a stable power density of 2.55 W m⁻². This work establishes a spatially decoupled platform for integrated freshwater production, salt harvesting, and auxiliary electricity generation, paving the way for decentralized zero-liquid-discharge brine valorization.