Superhydrophobic/Superoleophilic Polydimethylsiloxane-Coated Co3O4@ZnO-Modified 3D Metallic Foams for the Separation of Oil–Water Mixture and Emulsions

Abstract Oil–water separation presents a global challenge, mainly attributed to the rising incidents of oil spills during large-scale oil transportation and the discharge of substantial quantities of organic pollutants by industries. In this research, Co3O4@ZnO-PDMS-coated nickel foam (NF) and copper foam (CF) composites were successfully synthesized utilizing hydrothermal assisted dip-coating method. In situ grown Co3O4@ZnO hierarchical structure on three-dimensional (3D) metallic foams was coated using PDMS polymer. XRD data confirmed the formation of Co3O4 and ZnO phases in the as-prepared metallic foams. Vibrational bands of metal–oxygen and silicone (Si–C/Si–O–Si)-based bonds confirm successful PDMS deposition. Surface morphology demonstrates 3D interconnected pores with in situ Co3O4@ZnO hierarchical structure and PDMS coating. XPS analysis confirms the surface chemical states and elemental composition of Co3O4@ZnO-PDMS-coated NF and CF. As-prepared metallic foams exhibited superhydrophobicity with excellent WCAs of 152° ± 1.5° and 152° ± 1.1° and CAHs of 4.2° ± 1.0° and 6.5° ± 2.6°. Superhydrophobic/superoleophilic properties enabled the as-prepared metallic foam to show effective oil–water separation with a good flux range of 4710 ± 223 L m–2 h–1 to 8469 ± 110 L m–2 h–1, high separation efficiency (>97%), and reusability. The as-prepared metallic foam also enabled efficient gravity-driven surfactant-stabilized water-in-oil (W/O) emulsion separation with different surfactant concentrations, achieving a water rejection of up to 94.9%. The Cassie–Baxter wetting model interpreted the oil–water separation mechanism based on wettability measurements and intrusion pressure analysis. Co3O4@ZnO-PDMS-coated NF and CF composites retained hydrophobicity even after a thermal stability (50–200 °C) test and a strong acid–alkaline (pH 1–9) resistance test. Sandpaper abrasion cycle tests confirm its robustness, and by immersing in 3.5 wt % NaCl solution for 7 days, showed its anticorrosive properties.