Bio-Inspired Mesoporous Solar Evaporator Enabled by Upcycled PET

Solar-driven interfacial steam generation (ISSG) has emerged as a promising strategy for decentralized freshwater production. However, developing scalable solar evaporators that combine high evaporation performance, environmental compatibility, and stable operation under varying solar angles remains challenging. Here, we report a compound-eye-inspired three-dimensional solar evaporator based on graphite-containing PET nanofoam (GPF). The GPF was produced by upcycling polyethylene terephthalate (PET) waste. The nonsolvent-induced phase separation process produces a mesoporous and moldable structure with tunable water transport properties, enabling the construction of hemispherical multi-surface evaporators. This architecture provides angle-insensitive solar exposure and an enlarged water-wetted evaporative interface within a fixed projected footprint. As a result, the optimized evaporator achieved a projected-area-normalized evaporation rate of 3.44 kg m^{- 2} h^{- 1} under 1-sun illumination. In outdoor operation, the integrated evaporation-condensation module produced a freshwater yield of up to 24.4 kg m^{- 2} over 14 h under natural sunlight. The enhanced performance arises from the combined effects of expanded evaporation-active area, capillary-sustained water transport, side-surface evaporation, and internal heat redistribution. This result indicates that the 3D-CE improves evaporation through coupled transport and thermal effects, rather than through surface-area enlargement alone. This work presents a potential route for converting waste PET into functional solar evaporators for decentralized freshwater production.