Sandwich-structured wettability foam for highly efficient, cost-effective, salt-resistant, and durable solar desalination
Interfacial solar-driven vapor generation offers a sustainable route to freshwater, yet practical deployment is constrained by salt crystallization, high material costs, and thermal losses. This work reports a sandwich wettability structure (PNMF) comprising a polypyrrole-coated hydrophobic top layer, a hydrophilic melamine foam interlayer, and a tunable hydrophobic bottom layer. The PPy coating absorbs broadband solar radiation and retains heat in situ; the hydrophilic interlayer supplies water through interconnected microporous channels, forming confined water clusters that reduce evaporation enthalpy. The bottom layer's central hydrophobicity regulates water transport to balance supply and evaporation, while its hydrophobic edges provide self-floatability and minimize heat loss. Under 1 sun, the PNMF evaporator achieves 2.71 kg m−2 h−1 with ~90% solar-thermal conversion efficiency over 24 cycles. In 10 wt% NaCl simulated seawater, no salt crystals formed after 12 h, and the evaporation rate remained stable at 2.62–2.87 kg m−2 h−1 over 20 days. Under natural autumn sunlight (average irradiation <0.4 kW m−2, temperatures <24 °C), a portable device produced approximately 3 kg m−2 over 11 h, with purified water salinity below 0.14‰. The simple, low-cost design addresses salt accumulation and durability bottlenecks, offering a scalable pathway for decentralized freshwater production.