Full cattail leaf-based solar evaporator with square water transport channels for cost-effective solar vapor production

Solar vapor production is considered an effective and environmentally friendly method of reducing freshwater shortages. However, designing an affordable solar evaporator with a simple method is still a challenge. Herein, motivated by the transpiration of plants, a full cattail leaf-based solar evaporator has been developed. In this solar evaporator, the photothermal membrane has been exploited by simply cross-linking the carbonized cattail leaf and the fibers from the alkali-treated cattail leaf with sodium alginate. The original cattail leaf with its square water transport channels and inherent hydrophilicity is employed to pump the bottom water to the upper photothermal membrane. Thanks to the synergistic effect between the photothermal membrane and the cattail leaf-based water transporter, the full cattail leaf-derived solar evaporator acquires an evaporation rate of 1.46 kg m^–2 h^–1 with a solar thermal efficiency of 87.48% under 1-solar (1 kW m^–2). Fifteen-cycle experiments indicate that this solar evaporator has excellent stability. Outdoor experiments demonstrate that the full cattail leaf-based solar evaporator can effectively desalinate seawater and purify dyeing wastewater. Moreover, the total cost of the chemicals applied to manufacture 1 m² of cattail leaf-based photothermal membrane is approximately 3.1 dollars. This strategy is expected to turn freely available biomass into a potentially valuable solar evaporator with a simple cross-linking method and an affordable price that offers a promising future for alleviating the global freshwater crisis.