Stable Self‐Floating Reduced Graphene Oxide Hydrogel Membrane for High Rate of Solar Vapor Evaporation under 1 sun

Abstract Highly efficient vapor generation with considerable stability under natural solar irradiance is a promising technology for seawater desalination and wastewater purification. Here a broadband solar absorber of reduced graphene oxide hydrogel membrane (rGOHM), synthesized via an environmentally friendly one‐step hydrothermal reduction process, is demonstrated, which shows a high rate of solar vapor production and superior stability. The porous rGOHM containing more than 99.5% water within its small volume floats on the surface of water, exhibiting efficient solar absorption of ≈98% across 300–2500 nm, as well as sufficient water‐pumping pathways. The evaporation rate can be tuned by changing the water volume. By controlling the water volume, the self‐floating rGOHM can enable efficient interfacial solar vapor generation at a high rate of ≈2.33 kg m−2 h−1 under 1 sun, which is comparable to the rate generated by the evaporator with an extra insulator. In addition, the evaporation rate of rGOHM is only slightly affected at a high saltwater concentration (at least 15 wt%), and the rGOHM shows mechanical and physical stability. The superior evaporation performance combined with efficient eradication of wastewater contaminants, cost‐effectiveness, and straightforward fabrication process, makes this rGOHMs ideal for advanced high‐concentration seawater desalination and wastewater treatment technologies.