Magnetic supramolecular solvents: An efficient tool for extraction and photocatalytic degradation of dyes in textile wastewater

Abstract

The textile industry produces wastewater containing high levels of toxic dyes, which need to be removed before being discharged into the environment. In this study, supramolecular solvents (SUPRAS) with unique properties (magnetism, photocatalytic activity, nanostructures irreversibility, multiple polar/apolar/ionic binding sites, and reusability) were first developed for the simultaneous removal of neutral and charged dyes from textile effluents. The SUPRASs were synthesized using undecylenate oligomers as the basic unit for both chemisorption on magnetic iron oxide nanoparticles (MNPs) and coacervation induced by tetraalkylammonium salts. The tetrahexylammonium-induced magnetic SUPRASs showed an exceptional capability for the simultaneous extraction of cationic, anionic and neutral dyes under a wide range of experimental conditions (pH 3–9; NaCl 0.05–1 M; dye 10–250 mg L⁻¹), at V_SUPRAS/V_water ratios as low as 0.0025. The SUPRASs showed the same extraction efficiency for dyes in synthetic textile effluents (e.g. 98.9 % for acid red 88). The supramolecular aggregates making up the SUPRAS were highly stable; no residual oligomer or tetrahexylammonium ion were present in the treated water. The SUPRASs extracts containing the dyes were magnetically separated and subjected to UV light irradiation for dye degradation. Up to 97 % of acid red 88 was effectively degraded in the SUPRAS extract. Both dye extraction and degradation were virtually complete for at least three consecutive cycles using the SUPRAS, with no need for regeneration treatment. This research presents an innovative extraction-photocatalytic approach for efficiently removing dyes from textile wastewater that can easily be scaled up without raising environmental or health concerns.