Ligand-controlled Fe ₃ O ₄ nanoparticles as reusable adsorbents for dye removal in the chemical recycling of coloured polyester textiles

Chemical recycling of polyester through depolymerisation processes is a promising strategy to mitigate the environmental burden of polyester-containing textile waste. However, residual disperse dyes in depolymerised products often degrade the purity and whiteness of recovered monomers. Conventional dye removal methods, such as solvent extraction, frequently fail to achieve complete dye removal. Herein, we report the development of iron oxide magnetic nanoadsorbents capped with three hydrophobic ligands for the efficient removal of disperse dyes from monomer solutions. Strong hydrophobic interactions between the ligands and dye molecules significantly enhance adsorption efficiency. Systematic evaluation with different dyes reveals that molecular features such as contour length, polarisability, and flexibility strongly influence adsorption performance. The dye-adsorbed nanoadsorbents are readily recovered through magnetic separation and reused without structural degradation. By applying the nanoadsorbents to the decolourisation of depolymerised coloured textiles, we obtained highly pure white monomers suitable for repolymerisation into textile-grade materials. These findings highlight a sustainable and reusable nanomaterial platform for dye removal during the recycling of polyester textiles.