Bio-inspired Fabrication of SLS-MWCNTs Multifunctional Composite Membrane with Bionic Coating for Efficient Separation of Complex Oily Wastewater

Industrial development has led to the generation of large amounts of oily wastewater, which poses significant threats to both environment and human health. These wastewater streams often contain various pollutants, such as organic dyes and heavy metal ions, creating an urgent need for multifunctional materials capable of efficiently separating these contaminants. In this study, we deposited sodium lignosulfonate (SLS)-modified multi-walled carbon nanotubes (MWCNTs) onto polyvinylidene fluoride (PVDF) polymer membranes by vacuum filtration. Subsequently, a hydrophilic bio-inspired coating, consisting of pyrogallic acid (PG) and silane-coupling agent (KH550), was deposited on the membrane surface. The resulting composite membrane exhibited exceptional superhydrophilicity and underwater superoleophobicity. This membrane demonstrated high efficiency in separating various oil–water emulsions, with a separation efficiency reaching 99% and a stable separation flux maintained above 350 L m⁻² h⁻¹. The SLS-modified MWCNTs provided the membrane with abundant adsorption active sites, enabling excellent removal of cationic dyes and heavy metal ions. The removal rates of methylene blue (MB) and rhodamine B (RhB) exceeded 92% and 95%, respectively, while the adsorption capacities for Cu(II) and Pb(II) were 38.7 mg g⁻¹ and 46.8 mg g⁻¹, respectively. Furthermore, the composite membrane demonstrated outstanding chemical stability and durability under highly acidic, alkaline, and 5% NaCl salt solution conditions. Consequently, the SLS-MWCNTs@P/K-MF composite membrane holds great promise for the treatment of complex oily wastewater in extreme environments and has significant potential for remediation of wastewater contamination.