Large‐Scale Flat Silk Cocoons as a Highly Effective Salt‐Resistant Low‐Cost Solar‐Powered Evaporator

Solar seawater evaporators are a promising sustainable solution for freshwater production, yet they face challenges related to efficiency, evaporation rate, salt resistance, and the large-scale manufacturing of evaporative materials. Here, we demonstrate that flat silk cocoons (FSC), produced in large sizes (70 cm × 200 cm) by utilizing silkworms to spin silk fibers on flat surfaces, serve as evaporators with remarkable performance in salt resistance and evaporation. Specifically, the FSC s modified into a Janus-structured evaporator (FJE) by coating the top (thin) portion with superhydrophobic polydimethylsiloxane and the bottom (thick) portion with superhydrophilic polypyrrole. The Janus structure enables the FJE to transport water to the superhydrophilic/hydrophobic interface through its bottom portion and evaporate without salt precipitation. Simultaneously, the top portion absorbs sunlight and transfers heat to the bottom portion within the evaporator, promoting evaporation while minimizing heat loss. The FJE demonstrates exceptional cost-effectiveness (258.2 g h^-1 USD^-1), high evaporation rate (3.075 kg m² h^-1), and an impressive evaporation efficiency (79.73%). Notably, the superhydrophilic layer of the Janus structure enhances water exchange, enabling sustained evaporation for 18 h in 20 wt.% saline solutions without salt deposition under sunlight. The FJE represents a new generation of eco-friendly, cost-effective, salt-resistant, and thermo-localized evaporators.