Continuous and steady-state high-flux demulsification of oil-in-water emulsions by antifouling copper foam with composite superhydrophilicity-oleophobicity

Three-dimensional superhydrophilic materials hardly achieve continuous high-flux demulsification and separation for oil-in-water emulsions due to intrinsic oleophilicity leading to potential penetration of oil droplets through hydration layer and contamination on the surface over long-term separation processes. Constructing intrinsic oleophobic micro-regions on superhydrophilic surface can intensify anti-oil-fouling capacity for three-dimensional superhydrophilic materials. Herein, a composite superhydrophilic-oleophobic copper foam was prepared through co-deposition of aminated and fluorinated carbon nanotubes, skillfully introducing inherent oleophobic micro-regions on superhydrophilic interface to intensify anti-oil-adhesion capacity. Through a column technique, the modified copper foams achieved continuous demulsification of surfactant-stabilized and free oil-in-water emulsions without interruption for cleaning with high fluxes over 6000 and 10,000 L·m−2·h−1, and separation efficiencies over 95.1 % and 97.4 %, respectively. Various emulsions after demulsification transformed into immiscible oil–water mixtures, which can be quickly separated into pure oil and water at the aid of a second-step separation procedure by a superhydrophilic copper mesh. Importantly, the amount of recycled oil was consistent with that in feed emulsion during separation, indicating the accumulated oil in the copper foam could maintain dynamic equilibrium and a continuous and steady-state demulsification was achieved. The high-flux and continuous demulsification represents a significant breakthrough for superhydrophilic materials in the industrial application of oil–water separation.