Vertically aligned bilayer PTFE-based self-floating aerogels: monolithic salt-resistant evaporators enabled by coupled thermal and mass transport optimization

Monolithic bilayer PTFE-based aerogels with vertically aligned channels were fabricated. • PDA deposition regulated water transport for optimized evaporation and salt resistance. • Vertically aligned channels facilitated capillary water transport and Marangoni-driven salt back-diffusion. • The evaporator achieved an evaporation rate of 2.41 kg m -2 h -1 and over 95% retention. Solar-driven interfacial evaporation has emerged as a promising strategy for alleviating the global freshwater crisis. However, its practical application is hindered by the degradation of evaporation performance owing to salt accumulation and material aging. In this study, a bilayer polytetrafluoroethylene (PTFE)-based aerogel with vertically aligned microchannels is fabricated. Carbon nanotubes are encapsulated in the upper layer for efficient photothermal conversion, and polydopamine is controllably deposited on the PTFE skeleton to impart a hydrophilic functionality and regulate the water supply. Under one sun illumination, the evaporator achieves a high evaporation rate of 2.41 kg m −2  h −1 while self-floating in 3.5 wt% brine. Notably, the increased air–liquid interface in the channels promotes Marangoni convection, which synergistically promotes diffusion to actively recycle salt ions back to bulk water, thereby ensuring a salt-free evaporation interface for 15 days of continuous outdoor operation. Additionally, the evaporator demonstrates exceptional durability, retaining over 95% of its initial evaporation rate during a 14-day accelerated aging test. This study offers a simple and scalable design option for solar evaporators that combine long-term stability with excellent efficiency.