Controlling Superwettability by Microstructure and Surface Energy Manipulation on Three-Dimensional Substrates for Versatile Gravity-Driven Oil/Water Separation

Superwettable materials have gained tremendous attention because of their special wetting abilities. The key to obtaining and tuning superwettability is to precisely control the interfacial microstructures and surface energies of materials. Herein, we propose a novel approach to controlling the superwettability of three-dimensional foams. The surface microstructure was manipulated by the layer-by-layer covalent grafting of multidimensional nanoparticles (e.g., silica, carbon nanotubes, and graphene oxide), and the surface energy was tailored by grafting chemicals with different functional groups. This grafting approach improved the mechanical performance, reduced particle loading, and prevented particle disassociation, thereby increasing the absorption capacity and durability of the functionalized foams. More importantly, superhydrophobic/superoleophilic foams were obtained after heptanol grafting. They showed water contact angles of 153° in air and 158° in oil, an absorption capacity 113 times their weight gain, and a remarkable flux of 32.6 L m^-2 s^-1 for the separation of oil from water driven by gravity. Polydopamine grafting resulted in superhydrophilic/underwater superoleophobic foams that had an oil contact angle of 152° under water and a high flux of 19.3 L m^-2 s^-1 for the separation of water from oil. Thus, this study offers not only intelligent materials for versatile oil/water separation but also a profound approach for engineering high-performance superwettable materials.