Ice-Templated Zwitterionic Sponge Hydrogels for Stable and Efficient Solar Desalination in High-Salinity Brines

Solar-driven steam generation (SSG) offers a sustainable pathway for desalination, yet achieving temperature-regulated control over macroporous structures in salt-tolerant hydrogels remains a critical challenge. Here, we report a carbon black-coated PDMAPS sponge hydrogel (PDMAPS-CB-SH) fabricated via an ice-templated polymerization strategy, where the pore size and connectivity are tuned by regulating ice-crystal growth at different prefreezing temperatures. The optimized PDMAPS-CB-SH integrates abundant interconnected pores with the intrinsic antipolyelectrolyte effect of zwitterionic networks, enabling rapid water transport and stable swelling in brines up to 10 wt % NaCl. Upon incorporation of carbon black nanoparticles, the hydrogel evaporator achieves a high evaporation rate of 1.93 kg m⁻² h⁻¹ with an efficiency of 95.1% in seawater under 1 sun irradiation (1.0 kW m⁻²), and maintains stable evaporation performance under the tested high-salinity condition. Outdoor field tests further confirm its scalability, delivering 12.35 kg m⁻² day⁻¹ of freshwater with condensate quality meeting WHO drinking-water standards. This work establishes ice-templated zwitterionic sponge hydrogels as a versatile and scalable platform for efficient solar desalination, particularly under challenging high-salinity conditions.