Bio‐Inspired Mesoporous Solar Evaporator Enabled by Upcycled PET

ABSTRACT 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.