Superwetting charged copper foams with long permeation channels for ultrafast emulsion separation and surfactant removal

Abstract

Although the advanced materials for oil/water separation have been developing rapidly, few studies have focused on the issues of simultaneous emulsion breaking and surfactant elimination. Herein we fabricated superwetting positively charged and negatively charged copper foams by in situ growth of Cu(OH)₂ nanoneedles, accelerated the assembly of functional carbon nanotubes (CNTs) driven by electric field, and stacked them into a columnar separator with long permeation channels for ultrafast separation of oil-in-water emulsions and removal of surfactants. We proposed a separation strategy where lengthening the permeation channels of copper foams can prolong the residence time of emulsified oil droplets, which allows the copper foams to achieve both high efficiency and high flux. With superwettability, electrostatic interaction and long permeation channels, the positively charged copper foam can separate SDS-stabilized oil-in-water emulsions with a separation efficiency of up to 99.64% and permeation flux of up to 22 636.56 L m⁻² h⁻¹, while the negatively charged copper foam can separate DTAC-stabilized oil-in-water emulsions with a separation efficiency of up to 99.65% and permeation flux of up to 32 166.32 L m⁻² h⁻¹. More significantly, the two kinds of charged copper foams exhibited efficient removal ability toward anionic and cationic surfactants. The two superwetting charged copper foams with tunable permeation channel length could be a promising candidate for oil/water emulsion separation and surfactant removal in the laboratory and in industry.