Biomass-derived 3D solar evaporator with self-regeneration for water treatment

The development of sustainable and efficient solar-driven interfacial evaporation (SIE) systems is crucial for addressing global freshwater scarcity. Biomass-derived evaporators have garnered significant attention due to their abundant source availability, low cost, and eco-friendly sustainability. This study presents an innovative, self-regenerating 3D solar evaporator derived entirely from waste eggshells via a facile acid treatment and carbonization process. The inherent hierarchical porous structure of the eggshell enables rapid water transport, and the carbonized eggshell membrane serves as an excellent broadband (250-2500 nm) photothermal layer. Simultaneously, the natural ellipsoidal cavity structure of the eggshell provides self-buoyancy without external supports and acts as a light-trapping chamber to enhance solar absorption through multiple internal reflections. Benefiting from the porous structure and the ellipsoidal cavity structure, the optimized eggshell-derived evaporator achieves an exceptional evaporation rate of 3.09 kg m^-2 h^-1 under one-sun illumination with a photothermal conversion efficiency of 93.9%. Furthermore, outdoor testing under natural sunlight yields a total water production of 20.37 kg m^-2 and an average evaporation rate exceeding 2.50 kg m^-2 h^-1. This work presents a high-performance and stable biomass-derived solar evaporator, exemplifying the considerable promise of biomass materials as next-generation platforms for efficient solar-driven evaporation.