Willow Catkins-Derived Porous Carbon Membrane with Hydrophilic Property for Efficient Solar Steam Generation

Biomass wastes are abundant and common in our daily life, and they are cost-effective, promising, and renewable. Herein, collected willow catkins were used to prepare a hydrophilic biochar composite membrane, which was placed in a tree-like evaporation configuration to simulate a natural transpiration process. The strong light absorption (∼96%) of the biochar layer could harvest light and convert it into thermal energy, which then is used to heat the surrounding water pumped by a porous water channel via capillary action. A hydrophilic light-absorber layer remarkably increased the attachment sites of water molecules, thereby maximizing the use of thermal energy. At the same time, hierarchically porous structure and large specific surface area (∼1380 m² g^-1) supplied more available channels for rapid water vapor diffusion. The as-prepared composite membrane with a low-cost advantage realized a high evaporation rate (1.65 kg m^-2 h^-1) only under 1 sun illumination (1 kW m^-2), which was improved by roughly 27% in comparison with the unmodified hydrophobic composite membrane. The tree-like evaporation configuration with excellent heat localization resulted in the evaporator achieving a high solar-to-vapor conversion efficiency of ∼90.5%. Besides, the composite membrane could remove 99.9% sodium ions from actual seawater and 99.5% heavy metal ions from simulated wastewater, and the long-term stable evaporation performance proved its potential in actual solar desalination. This work not only fabricated an efficient evaporator but also provided a strategy for reusing various natural wastes for water purification.