Block Polymer-Functionalized Iron Oxide Nanoparticles for the Solid-Liquid Interfacial Extraction of Industrial Dyes: Sustainable Methodology Based on Molecular Interactions

Poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) block polymer-stabilized iron oxide magnetic nanoparticles (NPs) were used for the solid-liquid interfacial extraction of common water-soluble industrial dyes at room temperature. Extraction was performed under static conditions for an extended period of 24 h, as well as through the rapid titration method by adding polymer-functionalized magnetic NPs in aqueous dye solutions. It was simultaneously monitored by UV-vis measurements to quantitatively determine the amount of dye extracted. The titration method provided the rapid extraction of Coomassie Brilliant Blue (CBB) as well as Eriochrome Black T (EBT) in real-time within the time frame of the experiment. To understand the intermolecular interactions responsible for the extraction, dye-loaded magnetic NPs were analyzed by IR, XPS, TEM, and FESEM studies. All results indicated the participation of electrostatic interactions between surface-adsorbed hydroxyl functional groups of the polymer and aqueous solubilized dye molecules. The interactions were further enhanced by generating the ionic character on hydroxyl groups at low or high pH, which, in turn, facilitated the extraction. The methodology was highly sustainable and used the same sample of polymer-functionalized magnetic NPs repeatedly to extract an almost constant amount of dye in every cycle. Sustainability was achieved by changing the pH of the medium from low to high and vice versa, which acted as an on-off switch to the intermolecular interactions controlling the extraction. The applicability of the titration methodology was proposed as a simple and straightforward technique for cleaning water contaminated with water-soluble dyes in industrial effluents.