Rapid and Efficient Coacervate Extraction of Cationic Industrial Dyes from Wastewater

Effluent wastewater containing dyes from textile, paint, and various other industrial wastes have long posed environmental damage. Functional nanomaterials offer new opportunities to treat these effluent wastes in an unprecedentedly rapid and efficient fashion due to their large surface area-to-volume ratio. In this work, we explore a new approach of wastewater treatment using macroionic coacervate complexes formed with zwitterionic polyampholytes and anionic inorganic polyoxometalate (POM) nanoclusters to extract methylene blue (MB) dye as well as other cationic industrial dyes from model wastewater. Biphasic organic-inorganic macroion complexes are designed to produce a small volume of coacervate adsorbents of high density and viscoelasticity, in contrast to a large volume of supernatant solution for rapid and efficient dye removal. The efficiency of coacervate extraction is characterized by the adsorption isotherm and maximum MB uptake capacity against the concentrations of polyampholyte, POM, and LiCl salt using UV-vis spectrophotometry to optimize the coacervate formation conditions. Our macroionic coacervate complexes could reach nearly 99% removal efficiency for the model wastewater samples of varied MB concentration in <1 min. The extraction capacity up to ∼400 mg/g far surpasses the dye extraction efficiency of widely used activated carbon adsorbents. We also explore the regeneration of coacervate complexes containing high concentration of extracted MB by a simple Fenton oxidation process to bleach coacervate complexes for repeated POM usage, which shows similar MB extraction efficiency after regeneration. Hence, coacervate extraction based upon spontaneous liquid-liquid separating complexation between polyzwitterions and POMs is demonstrated as a rapid, efficient, and sustainable method for industrial dye wastewater treatment. In perspective, coacervate extraction could advantageously possess dual processing options in separation industry through either membrane fabrication or use directly in mixer-settlers.