Cellulosic fiber and aqueous effluent dye removal using deep eutectic solvents

Given the growing environmental concerns associated with the vast amounts of wastewater and solid waste produced by the textile industry, finding effective recycling strategies to reintegrate these materials into the production cycle has become essential. This study explores the use of two eco-friendly deep eutectic solvents as sustainable solutions for dye removal from both aqueous media and cotton fabrics, thereby facilitating their recyclability. The solvents -both based on ammonium salts- were formulated using either tetrahexylammonium bromide (THAB) with ethyleneglycol (EG) to produce a hydrophobic solvent adequate for liquid-liquid extractions or tetramethylammonium hydroxide pentahydrate (TMAH·5H₂O) with urea, a hydrophilic solvent to put in contact with the fabric. They demonstrated strong extractive capabilities for the two most common classes of textile dyes: reactive and direct. Physicochemical characterization of these solvents was carried out to check their stability. Extraction conditions were optimized from both types of matrices, achieving efficient dye removal (> 95 %) using a 1:20 ratio of fabric/DES and a ratio as high as 1:3900 (DES/aqueous phase). To test the structural integrity of the cotton fibers, size-exclusion chromatography was employed to assess potential degradation, confirming that fabric quality remained within acceptable limits to allow for subsequent recycling applications.