Phase-change photothermal foam enables continuous hypersaline brine desalination

Seawater desalination is critical for mitigating global freshwater scarcity, yet the discharge of high-salinity brine causes severe ecological and economic issues. Solar-driven interfacial evaporation provides an energy-efficient method for achieving zero liquid discharge and effective brine concentration. To manage the inherent intermittency of natural sunlight, phase change materials are increasingly integrated to store excess thermal energy for continuous evaporation. Nevertheless, current systems are limited by elevated phase-transition temperatures, liquid leakage, and substantial performance degradation in hypersaline conditions. Here we show a multifunctional composite foam that unifies broadband photothermal conversion with low-temperature phase-change thermal regulation for sustained hypersaline desalination. By confining dodecylamine within a polypyrrole-coated chitosan-phenolic network, our material achieves a 95% solar absorption efficiency and a phase-change energy storage capacity of 208.4 J g^-1. The evaporator achieves a stable evaporation rate of 1.862 kg m^-2 h^-1 under one sun and maintains 0.684 kg m^-2 h^-1 in the absence of light. It also sustains a high evaporation rate of 1.763 kg m^-2 h^-1 in 20 wt% NaCl without salt accumulation and produces 9.229 kg m^-2 of purified freshwater over 10 h of outdoor solar operation. These findings provide a scalable and continuous approach to solar-driven brine reduction, advancing sustainable resource recovery and all-weather water purification.