Innovative approaches in wastewater treatment: kinetic and isotherm investigation of dye adsorption on sulfur-modified PET fibers

Abstract This study demonstrates the efficacy of sulfur-modified polyethylene terephthalate fibers (CS 2 -NaOH-IDA/GMA-PET) for the removal of methylene blue dye from aqueous solutions. Sulfur-containing xanthate structure was formed on PET fibers by innovative chemical modifications. Thus, the adsorption capacity and surface reactivity of the fibers were increased. The fibers exhibited optimal adsorption at a pH of 8, with a maximum capacity of 129.87 mg/g, while the adsorption kinetics followed a second-order model (q e = 7.5 mg/g, R 2 = 0.9985). Isothermal and thermodynamics studies have been also performed. The results showed that the Langmuir isotherm fitted the experimental results. And thermodynamic parameters such as ∆G°, ∆H° and ∆S° were calculated. The adsorption of methylene blue on CS 2 -NaOH-IDA/GMA-PET fibers is a spontaneous and endothermic process. Fourier-transform infrared spectroscopy and scanning electron microscopy analyses confirmed structural changes, and thermogravimetric analysis revealed reducing thermal stability due to the incorporation of functional groups. According to desorption and reusability studies, CS 2 -NaOH-IDA/GMA-PET fibers can be reused at least five times without significant change in the removal efficiency of MB dye. This study presents a novel approach by chemically modifying PET fibers through successive functionalization with GMA, IDA, NaOH, and CS 2 , resulting in a multi-functional adsorbent surface enriched with hydroxyl, carboxyl, amine, and sulfur-containing groups. Unlike conventional adsorbents, this composite demonstrates enhanced surface reactivity, high adsorption capacity, and excellent reusability. The use of PET as a base material also offers a sustainable and cost-effective alternative for industrial dye removal applications. Graphical abstract