Sodium alginate-based biomimetic crack-network Janus foam evaporator toward robust solar desalination, wastewater purification, and thermoelectric power generation

Solar-driven interfacial evaporation is promising for sustainable freshwater production but faces challenges like salt accumulation and energy loss. Inspired by the crack networks in chameleon skin, we developed a three-dimensional Janus foam evaporator (3D-JRSMP) with engineered micro-cracks. It is constructed by anchoring recycled carbon fibers in a melamine foam scaffold integrated with a sodium alginate (SA) hydrogel. The Ca 2+ crosslinked SA forms a hierarchical crack network for enhanced water transport and light harvesting. A top polydimethylsiloxane coating creates a superhydrophobic/superhydrophilic Janus interface for efficient heat localization and salt rejection. Crucially, the SA hydrogel facilitates the formation of “intermediate water”, substantially reducing evaporation enthalpy. The evaporator achieves an evaporation rate of 4.98 ± 0.12 kg m −2  h −1 and a solar-to-vapor efficiency of 97.29 ± 0.03% under 1 sun irradiation. It maintains stable performance in 20 wt% brine over 20 cycles and effectively purifies water containing heavy metals, dyes, and antibiotics. By leveraging the evaporation-induced temperature gradient, an integrated thermoelectric system delivers 305.1 ± 4.6 mW m −2 . Outdoor desalination yielded 29.8 ± 0.4 kg m −2 of freshwater in 10 h. This work presents a scalable platform combining bioinspired design, upcycled materials, and polysaccharide-enabled low-enthalpy evaporation for integrated water and energy harvesting.