Graphene Oxide Assemblies for Sustainable Clean-Water Harvesting and Green-Electricity Generation

Conspectus The urgent problems of water scarcity and the energy crisis have given rise to the development of a range of sustainable technologies with the great advancement of nanotechnologies and advent of attractive nanomaterials. Graphene oxides (GO), a derivative of graphene with an atom-thin thickness and abundant oxygen-containing functional groups (such as -OH, -COOH), are water-soluble and can be assembled into a variety of structures (such as fiber, membrane, and foam) with great potential in environmental and energy-related fields. As a typical precursor of graphene, GO can be easily reduced to graphene by chemical or thermal treatments to demonstrate excellent photothermal properties as well as tunable thermal conduction, which is highly desirable for efficient solar-driven water evaporation. The intrinsic large specific area of GO nanosheets can provide enough sites for ions adsorption and its porous assemblies facilitate the transport of water. In addition, the abundant functional groups allow the spontaneous adsorption of water molecules from the ambient environment and give birth to movable ions (usually protons) under the solvation effect. Once a chemical gradient is formed on the component, a remarkable electricity is generated from the directional transport of protons. Thanks to the excellent chemical properties of GO nanosheets, a wide range of assemblies with 1D aligned fibers, 2D layered membranes and 3D porous foam can be easily fabricated by wet-spinning, solution-filtration, and freezing-drying methods. The various GO assemblies are able to exhibit abundant functions with remarkable weaving capability for GO fibers, superior flexibility for GO membranes, and exceptional adsorption capacity for GO foams. In light of all the advantages, GO and its assemblies are remarkably promising in the fields of sustainable development to meet the pressing challenges of water and energy crisis.In this Account, we will discuss the progress of clean-water production and green-electricity generation technologies based on GO assemblies. The fundamental working mechanism, optimization strategies, and promising applications are explored with an emphasis on the materials development. We also discuss the functions of GO assemblies in the water and electricity generation process and present their limitations and possible solutions. Current challenges and promising directions for the development of clean-water production and green-electricity generation are also demonstrated for their realistic implementations. We anticipate that this Account would promote more efforts toward fundamental research on graphene functionalization and encourage a broad exploration on the application of graphene assemblies in clean-water production and electric power generation systems.