Asymmetrically Wettability Janus Cotton Fabrics Fabricated via Interfacial Ion Migration for Surfactant-stabilized Oil-in-water Emulsions

Abstract Separation of surfactant-stabilized oil-water emulsions seems to be challenging owing to its diverse repercussions on environment and human life. The asymmetrical wettability Janus cotton fabric (J-MH@CF) with high separation performance was prepared by two-step method, which related to interfacial ion migration technology and unilateral spraying treatment. In detail, the immobilization of magnesium hydroxide (Mg(OH)2) caused the formation of the rough micro/nanostructure of cotton fabric surface, which was helpful to superhydrophilic property. Stearic acid as a coating created the unilateral superhydrophobic surface with low surface energy. J-MH@CF showed asymmetric wettability, featuring diode-like directional water transmission. Wettability, directional transmission and separation performance of J-MH@CF membrane were investigated systematically. The asymmetric wettability architecture was demonstrated to play a key role in separating surfactant-stabilized oil-in-water emulsions. Impressingly, the separation performance was not affected by the type of surfactants. For emulsion stabilized by sodium dodecyl sulfate (SDS), the separation flux driven by gravity was approximately 500 L m-2h-1, and all separation efficiencies were over 99.3%. CTAB/Oil/H2O emulsion and the Tween-60/Oil/H2O emulsion also could be successfully separated with high separation efficiency and separation flux. During the whole separation process, the oil droplets surrounded by surfactants (Oil-Ss) were difficult to demulsify and gathered on the surface of the fabric to form a "creamy layer", which was beneficial to improve separation efficiency and could be cleaned off so that J-MH@CF membrane was not contaminated. In addition, the J-MH@CF membrane exhibited robust reusability for separation, which was promising for remediation of oily wastewater containing surfactants.