Sandwich-Structured Superhydrophobic Coating for Rapid and Ultrahigh-Efficiency Viscous Oil Separation from Water

Oil spill accidents on the sea and oily wastewater produced in daily life have posed serious threats to the environment. Therefore, there is an urgent need for a material that can effectively separate these mixtures using simple operations. Herein, an ecofriendly sandwich-structured coating with excellent superhydrophobic/superoleophilic properties was fabricated by in situ growth on copper mesh and cotton fabric substrates. Specifically, using the versatility of tannic acid (TA) film, including chelation and reduction with Cu²⁺, flower-like Cu₂S@CuO can be in situ grown on a copper mesh or fabric surface. Then, the Schiff base reaction between TA and octadecylamine is used to hydrophobically modify the surface. Water contact angle (WCA) of the sandwich-structured TA-Cu₂S-TA-ODA-coated copper mesh and fabric can reach 160.8 and 156.3°. The coated copper mesh can be folded into a miniature container to collect oil, with collection efficiency reaching 96.47%. And the collection efficiency can be above 90% even after 10 cycles, and its WCA is still 155°. Besides, it can quickly separate various oils. Even for highly viscous peanut oil, the separation efficiency and flux can reach 90.7% and 0.038 mL·cm^-2·s^-1, respectively, which are much higher than those reported by other similar studies. Furthermore, the coating can endow cotton fabrics with excellent UV-shielding performance compared to the original cotton fabrics. In particular, even after 100 tape peeling tests, 7 washing cycles, 1 h of continuous strong UV irradiation, or 24 h of organic solvent soaking, the sandwich-structured TA-Cu₂S-TA-ODA coating still has superhydrophobic properties.