Facile fabrication of 3D Janus foams of electrospun cellulose nanofibers/rGO for high efficiency solar interface evaporation

Solar-powered interfacial evaporation is one of the most efficient state-of-the-art technologies for producing clean water via desalination. Herein, we report a novel bio-based nanofibrous foam for high efficiency solar interface evaporation. To this end, a hybrid membrane of cellulose nanofibers/graphene oxide (GO) is first fabricated by electrospinning coupled with in situ layer-by-layer self-assembly technique. After that, the membrane is subjected to a foaming process in an aqueous NaBH4, which effectively transforms the 2D membrane into a 3D foam. This structure can improve the photothermal conversion efficiency and also facilitate the water transport at the gas-water interface. In the meantime, the GO is converted to the reduced GO (rGO) with a higher light absorption efficiency. Finally, one side of the foam is hydrophobically modified via spray-coating with a fluorocarbon resin (FR) to obtain the Janus type 3D foam, namely FR@EC/rGO. The resultant 3D foam combines the functions of solar energy absorption in the upper layer and water pumping capability in the lower layer. It exhibits an extraordinary solar vapor conversion efficiency of 94.2 % and a fast evaporation rate of 1.83 kg m−2 h−1, showing high potential in future seawater desalination.