Salt-responsive evaporation behavior of chitosan-based hydrogels: driven by dual-mechanism synergy for efficient seawater desalination

Abstract

Developing solar-driven interfacial water evaporators based on marine bioderived polymers represents a highly promising and sustainable strategy to address the global freshwater scarcity crisis. However, the inherent high crystallinity of native chitosan restricts the accessibility of its hydrophilic functional groups, thereby severely constraining its potential for efficient water activation. Herein, a strategy for facilitating water activation through reduced crystallization of polymers is proposed to fabricate a salt-responsive chitosan-based hydrogel evaporator with vertically aligned porous architectures. Critically, the resulting hydrogel exhibits an anomalous salinity-induced evaporation enhancement. Meanwhile, based on the Hofmeister effect, chaotropic ions in seawater, such as Cl -, can effectively penetrate the polymer network, disrupting the interchain hydrogen-bonding network of chitosan. This process significantly reduces the crystallinity of chitosan and liberates a larger number of hydrophilic functional groups. The salt-induced water activation mechanism enables the salt-responsive hydrogel evaporator to achieve an evaporation rate as high as 2.98 kg m -2 h -1 in 3.5 wt% NaCl solution, outperforming that in pure water (2.32 kg m -2 h -1 ). Furthermore, the evaporator features excellent salt tolerance under high-salinity conditions and achieves nearly 100% removal efficiency for both ionic species and organic contaminants. This work not only develops a green, high-performance solar-driven interfacial water evaporator, but also provides new mechanistic insights into strengthening interfacial evaporation by regulating polymer networks using salt ions.