A Self-Floating, Self-Insulating, and Janus Evaporator Inspired by Victoria Amazonica

Solar-powered photothermal evaporators offer a sustainable approach for freshwater extraction. Nevertheless, their practical application is hindered by the difficulties in integrating thermal insulation, self-flotation, and efficient water transport within a single device. Inspired by the structure of Victoria Amazonica, a fiber-based solar steam evaporator is developed, featuring self-floating, self-insulating, and unidirectional water-transfer. The design employs a Janus nonwoven (JN), fabricated by precisely adjusting the weight ratio of a hydrophilic viscose (VIS) fiber web and a hydrophobic polypropylene/polyethylene (PP/PE) core-sheath fiber web, followed by a needle punching process to bond them together. The resulting high fluffiness and vertically aligned fiber pillars form continuous water channels across the JN thickness. This structure enables ultralow thermal conductivity (< 0.05 W mK^-1), minimal conductive heat loss (0.6%), sustained water supply, and rapid salt ion diffusion, leading to a high photothermal conversion efficiency of 90.8%. More attractively, the evaporator maintains permanent buoyancy on seawater, since its density (1.06 g cm^{- 3}) is even lower than that of seawater (1.07 g cm^{- 3}). By integrating biomimetic structural engineering with scalable and affordable fabrication, this work may provide a competitive pathway to tackling global freshwater scarcity while enhancing the design of high-performance solar desalination systems.