Biomass-enhanced Janus sponge-like hydrogel with salt resistance and high strength for efficient solar desalination

Interfacial solar-driven evaporation technology shows great potential in the field of industrial seawater desalination, and the development of efficient and low-cost evaporation materials is key to achieving large-scale applications. Hydrogels are considered to be promising candidates; however, conventional hydrogel-based interfacial solar evaporators have difficulty in simultaneously meeting multiple requirements, including a high evaporation rate, salt resistance, and good mechanical properties. In this study, a Janus sponge-like hydrogel solar evaporator (CPAS) with excellent comprehensive performance was successfully constructed. The introduction of biomass agar (AG) into the polyvinyl alcohol (PVA) hydrogel backbone reduced the enthalpy of water evaporation, optimized the pore structure, and improved the mechanical properties. Meanwhile, by introducing hydrophobic fumed nano-silica aerogel (SA) and a synergistic foaming-crosslinking process, the hydrogel spontaneously formed a Janus structure with a hydrophobic surface and hydrophilic bottom properties. Based on the reduction of the evaporation enthalpy and the modulation of the pore structure, the CPAS evaporation rate reached 3.56 kg m^-2 h^-1 under one sun illumination. Most importantly, owing to the hydrophobic top surface and 3D-interconnected porous channels, the evaporator could work stably in high concentrations of salt-water (25 wt% NaCl), showing strong salt resistance. Efficient water evaporation, excellent salt resistance, scalable preparation processes, and low-cost raw materials make CPAS extremely promising for practical applications.