Ultra-low voltage modulated water-selective permeation for on-demand separation of oil/water emulsions based on the facilely prepared laminar membranes with high conductivity

Abstract

Smart membranes with stimuli-modulated liquid-selective permeation hold promise for on-demand separation of oil/water mixtures, yet the facile preparation of membranes with sensitive and easily implemented responsiveness still remains a challenge. Herein, we present the sensitive manipulation of water-selective permeation using a weak electric field with ultra-low voltages and the resulting on-demand separation of oil-in-water emulsions on a facilely prepared laminar membrane. Fabricated via simple vacuum filtration, the MXene membrane possesses high conductivity and molecule-scaled transport channels, both of which facilitate the sensitive modulation. A voltage of just several negative volts (−4 V) can significantly switch the wetting and permeation of water on the membrane, which is distinctly lower than that previously reported (hundreds of volts and even several kV). In addition, the negatively charged membrane, under the applied bias, enhances the rejection of surfactant-wrapped oil droplets, preventing the fouling of material surfaces. Consequently, the separation of oil-in-water emulsions was achieved with high oil rejection rate (99 %) and considerable flux for a variety of oil types and percentages. Particularly for the crude oil/water mixtures, the rejection rate reached 99 % and the flux achieved 69.72 L m⁻² h⁻¹. This study presents a novel example for achieving easy and economical smart separation of oil/water mixtures using highly conductive materials, and should also spark research in areas such as water purification, drug delivery, microfluidic valves, etc.