Oil/water separation on structure-controllable Cu mesh: Transition of superhydrophilic-superoleophilic to superhydrophobic-superoleophilic without chemical modification

Four different surface morphologies, including needle-like, bamboo leaf-like, pine needle-like, and peony flower-like structures, were prepared on Cu mesh surface, and the existence of these different surface morphologies were due to the formation of Cu(OH)(2) or CuO microstructures by controlling the oxidation time and oxidation temperature of the chemical reaction. These freshly prepared Cu meshes all exhibit superhydrophilic-superoleophilic after dried with a hair dryer. They all have excellent separation efficiency, and the separation efficiency for oil-remove (similar to 96%) is higher than that of water-remove (similar to 94%). Interestingly, these meshes with four different surface morphologies can transform from superhydrophilic-superoleophilic to superhydrophobic-superoleophilic just after storage in air for > 20 days without any further chemical modification. This is because oxygen adsorption on the mesh surface contributes to air trapped into the microstructures. These superhydrophobic-superoleophilic copper meshes have good durability. According to the investigation of separation efficiency of the superhydrophobic-superoleophilic mesh, we find that the separation efficiency for oil-remove of the superhydrophobic-superoleophilic mesh (similar to 99%) is higher than that of the superhydrophilic-superoleophilic mesh (similar to 96%).