Self-assembled superhydrophilic MOF-decorated membrane for highly efficient treatment and separation mechanism of multi-component emulsions

Complex multi-component pollutant-oil-water emulsions have caused serious environmental problems and increased the difficulty of purification treatment in the last few decades. The membrane based on two-dimensional (2D) materials can rationally control the interlayer distance, thus improved the separation performance of the membrane for complex wastewater. We herein reported a composite membrane, in which 2D metal-organic frameworks (MOFs) Co-CAT-1 with super-hydrophilicity cross-linked by polyethylene imine (PEI) was integrated into graphene oxide (GO) and then coated on polyvinylidene fluoride (PVDF) membrane (CPG membrane). The CPG membrane exhibited highly efficient in separating oil-water (including crude oil) emulsions, achieving a flux of 219 L∙m⁻²∙h⁻¹∙bar⁻¹ and a separation efficiency of 99.2 %. Moreover, the separation efficiency for complex emulsions after several cycles was maintained >99 % for dyes and 76 % for heavy metal ions (Ni²⁺, Pb²⁺, Zn²⁺). The remarkable fouling resistance and reusability of CPG membrane in purifying complex oil-in-water emulsions can be attributed to their internal cross-linking, electrostatic interactions, hydrogen bonding attraction, and π-π stacking. Molecular dynamics simulations were employed for in-depth studies on the separation processes of dye- and heavy metal ions-emulsions, revealing the mechanisms of mass transfer within the membrane. This work aims to construct stable and multifunctional membranes for separating pollutant-oil-water emulsions with multi-component.