Quick and Reversible Superwettability Switching of 3D Graphene Foams via Solvent-Exclusive Microwave Arcs

For highly active electron transfer and ion diffusion, electrically and thermally conductive 3D graphene foams (3D GFs) heavily rely on precise control of their surface wettability with respect to different polarities of fluids. For their practical applications, either hydrophilic or hydrophobic 3D GFs are prepared in advance; even though there have been many different ways of controlling their surface wettability, such as solvent treatment, heteroatom doping, ultraviolet or laser irradiation, and plasma treatment, they are time-consuming and even high-cost processes, limiting them to be only applicable for 2D graphene or powders. Here, we present ultra-simple and rapid superwettability switching of 3D GFs in a reversible and reproducible manner, as mediated by solvent-exclusive microwave arcs. As the 3D GFs are pre-coated with vaporized solvents exclusively, short microwave radiation (≤10 s) leads to plasma hotspot-mediated production of polar or nonpolar radicals. Upon immediate radical chemisorption, the 3D surfaces become either superhydrophobic (water contact angle = ~170°) or superhydrophilic (~0°), and interestingly, the dramatic wettability transition can be repeated many times due to the facile exchange between previously chemisorbed and newly introduced radicals<i>.</i> Our microwave-mediated, quick and reversible wettability switching would be applicable for many different applications (e.g., energy storage, sensing, microfluidic transportation, and water-oil separation). Importantly, our superwettability switching is applicable for all kinds of carbon-based nanomaterials, including 2D graphene and carbon nanotubes.