Double-layer Janus sponge evaporator: Optimal balancing between evaporation efficiency and salt resistance

In recent years, solar-driven interfacial evaporation materials for seawater desalination and wastewater treatment have garnered significant interest. Hydrogels are considered promising candidates due to their high evaporation rates. However, traditional hydrogel-based solar evaporators are limited by the poor salt resistance and deteriorated mechanical properties. This work successfully constructed a Janus PSPH@CP double-layer solar evaporator with excellent comprehensive performance. It consists of a hydrophobic C/PDMS (CP) coating and a hydrophilic PSPH substrate using polyurethane foam (PU) as skeleton, with its pores filled with the SA/PVA hydrogel and hollow SiO 2 micro-spheres. The superhydrophobic carbon-containing upper coating provides robust light absorption capacity (97 %) and effective salt resistance, while the lower PU foam provides the solar evaporator a solid porous framework with excellent mechanical property. The SP hydrogel, which wraps the inner wall of the PU, is used as a water transport medium due to its superhydrophilic network. Finally, the hollow SiO 2 micro-spheres are embedded in the pores to enhance thermal insulation and optimize thermal management. The integration of the hydrogel and hollow SiO 2 microspheres optimized evaporation enthalpy and thermal management, resulting in an evaporation rate as high as 2.72 kg m -2 h −1 . Meanwhile, the asymmetric wetting characteristics of the solar evaporator’s enable strong salt resistance. As a result, an optimal between the evaporation efficiency and salt resistance is obtained in the fabricated PSPH@CP solar evaporator. The efficient water evaporation, excellent salt resistance, straightforward large-area preparation, and low-cost raw materials suggest that the Janus PSPH@CP solar evaporator has broad prospects for practical applications.