Closed Pore Structured NiCo2O4-Coated Nickel Foams for Stable and Effective Oil/Water Separation

To solve the serious problem caused by oily wastewater pollution, unique interface designs, for example, membranes with superwetting properties such as superhydrophobicity/superoleophilicity and superhydrophilicity/underwater superoleophobicity, provide a good way to achieve oil/water separation. Here, inspired by the liquid storage property of the honeycomb structure, we propose a strategy to fabricate NiCo₂O₄-coated nickel foams for stable and efficient oil/water separation. NiCo₂O₄ with a closed-pore structure was formed by assembling nanoflakes with a micro/nanoscale hierarchical structure. Compared with nickel foam coated by NiCo₂O₄ with an open-pore structure (NiCo₂O₄ nanowires), the enclosed nanostructure of NiCo₂O₄ nanoflakes can firmly hold water for a more stable superhydrophilic/underwater superoleophobic interface. As a consequence, the NiCo₂O₄-nanoflake-coated nickel foam has a larger oil breakthrough pressure than the NiCo₂O₄-nanowire-coated nickel foam because of a slightly larger oil advancing angle and a lower underwater oil adhesion force, which makes it more stable and efficient for oil/water separation. Moreover, the NiCo₂O₄-coated nickel foams have excellent chemical and mechanical stability, and they are reusable for oil-water separation. This work will be beneficial for the design and development of stable underwater superoleophobic self-cleaning materials and related device applications, such as oil/water separation.