Tailoring Ionization of Hyper-Cross-Linked Hydrogels for Solar-Driven Crystallization of Ultrahigh-Salinity Brines.

Abstract

Desalination technologies inevitably generate concentrated brine, the treatment of which remains a major bottleneck to the implementation of zero-liquid-discharge systems. Evaporative crystallization offers a direct route to complete salt recovery, but it is intrinsically energy-intensive and becomes increasingly inefficient at high salinity because of the diminished evaporation driving force. Photothermal interfacial evaporation improves solar energy utilization, but salt accumulation and crystallization at the evaporation interface inevitably degrade operational stability in high-salinity systems. Here, we introduce a hydrogen-bond-enhanced ionization of cross-linking points (HIC) strategy in a hyper-cross-linked hydrogel membrane to decouple the crystallization interface from the photothermal evaporation interface. The HIC-gel membrane, constructed from sodium carboxymethylcellulose and hydroxyethyl cellulose, contains densely hydrogen-bonded microcavities with regulated cross-linking distances. Cooperative ionization within these microcavities induces counterion condensation and a self-limiting ion-blocking effect while preserving rapid water transport through the hydrogen-bond network. This selective ion regulation suppresses salt crystallization at the evaporation surface, enabling continuous solar-driven crystallization of saturated brine. The HIC-gel membrane-enabled crystallizer operates stably for more than 10 days without regeneration or maintenance in a natural outdoor environment, delivering an average daily salt yield of 2.8 kg m^-2. The HIC design enables separation of crystallization from evaporation, providing a route toward durable solar-driven terminal brine management for ultrahigh-salinity brine crystallization.