Electric field regulated wettability switching of three-dimensional nickel foam for on-demand separation of multiple emulsions and flux self-recovery.

During petroleum extraction and refining processes, a large amount of stable emulsions is generated, which are difficult to separate and severely hinder oil-water resource recovery and continuous processing. To address the limitations of conventional single-wettability materials, which are typically suitable for only one type of emulsion and prone to pore blockage during continuous operation, a three-dimensional composite with electrically switchable wettability, SiO2@NF-AOT/PPy, is developed by integrating nickel foam, SiO2 nanofibers, and an electro-responsive functional layer. The unique feature of this system lies in its reversible, electrochemically regulated interfacial wettability, enabling on-demand switching between hydrophilic/underwater oleophobic and hydrophobic/oleophilic states, enabling on-demand separation of oil-in-water, water-in-oil, and more complex emulsions. Meanwhile, electrochemical switching promotes the release of retained phases within the pores, restoring flux and mitigating fouling. The separation efficiencies for water-in-toluene and toluene-in-water emulsions reach 99.0% and 98.7%, with corresponding fluxes of 8636.51 and 11077.26 L·m-2·h-1, respectively. During the continuous separation of 1000 mL of emulsion, the separation efficiency remains above 98%, and the flux recovery ratio reaches 92%-95% after wettability switching. In addition, the material exhibits good applicability to different oil systems, achieving efficient separation for both 1,2-dichloroethane emulsions and high-viscosity lubricating oil emulsions. For multiple emulsions (W/O/W and O/W/O), stepwise separation of oil and water phases can be achieved, with flux maintained at the 103 L·m-2·h-1 level and separation efficiencies higher than 98%. In more complex industrial diesel cracking systems, the separation efficiency still exceeds 92.7%, and flux recovery can be realized through wettability switching. Therefore, SiO2@NF-AOT/PPy enables efficient, stable, and switchable separation of various oil-water emulsions while possessing interfacial regenerability, providing a distinctive electro-responsive strategy for the continuous treatment of complex emulsions.