Graphene Oxide–Reduced Graphene Oxide Janus Membrane for Efficient Solar Generation of Water Vapor

Water purification by solar distillation technique is considered a sustainable method of producing fresh water. Thus, the development of a highly efficient solar absorber system has gained considerable attention. In this study, we report a graphene oxide (GO)–reduced graphene oxide (rGO) Janus membrane produced via laser treatment of the GO membrane under the protection of hydrogel. One side of the GO membrane is reduced to rGO using laser power, while the other side of the GO membrane is protected by hydrogel to avoid laser ablation and retain the integrity and original state of the membrane. The hydrophilicity of the GO layer and the relative hydrophobicity of the rGO layer complement each other and work synergistically. The hydrophilic GO side provides a good water transmission channel and exhibits good block salt penetration, whereas the relatively hydrophobic rGO side with a 3D rough surface increases the evaporation rate by increasing the sunlight absorption. Therefore, the resultant GO–rGO Janus membrane under 1 sun illumination exhibits a high solar-to-vapor efficiency of 91.4%, which is higher than that of most graphene-based photothermal conversion materials previously reported. Simultaneously, it is found that the GO–rGO Janus membrane is highly efficient and salt resistant and can be utilized for the purification of various types of water, including seawater and supersaturated brine. Therefore, the GO–rGO Janus membrane made may help to collect solar energy, and this research can be considered as a useful attempt to develop an efficient Janus membrane for producing fresh water.