Abstract
Oil-water separation using super-wetting and the selective permeability of membranes for oil or water has great ecological and economic significance. We report on the transition of wettability response, from superhydrophilic underwater-superoleophobic to superhydrophobic-superoleophilic state, by nanostructuring stainless steel and copper meshes using ultrashort femtosecond laser pulses. Our approach is environment-friendly, chemical free, and efficient as it exploits the benefit of aging the processed samples in a high vacuum environment. We optimized the laser scanning parameters, mesh pore size, and aging conditions to produce membranes exhibiting an extraordinary separation efficiency of 98% for the oil-water mixture. A variation in the water and oil contact angles for different meshes is presented as a function of the laser scanning speed. Stainless steel meshes with 150 μm pore size and copper meshes with 100 μm pore size have demonstrated an excellent wettability response for oil and water phases. Vacuum aging causes rapid chemisorption of hydrocarbons on laser-structured surfaces in the absence of water molecules, rapidly transforming the wetting state from superhydrophilic to superhydrophobic.
Highlights
Oil-water separation has great ecological and economic significance
We report on the transition of wettability from superhydrophilic underwater-superoleophobic to superhydrophobic-superoleophilic states by nanostructuring stainless steel and copper meshes using a high repetition rate femtosecond fiber laser
Water contact angles of 145.2◦ and 141.1◦ were obtained for 500 μm copper mesh kept in a high vacuum after laser structuring at scanning speeds of 100 and 300 mm/s, whereas samples aged in air showed smaller water contact angles (134.2◦ and 132.7◦, respectively)
Summary
Oil-water separation has great ecological and economic significance. Organic industrial waste mixed with water during metal processing, oil refining, and food processing requires efficient oil separation and treatment before disposal (Milicet al., 2013). Those superhydrophilic meshes showed a superoleophobic response under water, with oil contact angle (OCA) ranging from 155 to 163◦ across all scanning speeds and metal mesh types (see Supplementary Figures 2, 3 in the supplementary data file).
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