Synthesis of hydrogel adsorbent from PET waste bottles for efficient removal of anionic Azo dye congo red and heavy metal ions from aqueous solution

This study investigates the synthesis and characterization of hydrogel obtained from polyethylene terephthalate (PET) waste as an adsorbent in the treatment of water from dyes and heavy metals. Aminoylsis method for depolymerization of PET waste was used. Hydrogels were synthesized at four different concentrations of crosslinking agent, ethylene glycol diglycidyl ether (EDGE) at 15%, 16.5%, 18%, and 19.5%. Characterizations such as morphology and structure of derived hydrogel were found out using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR), accordingly. Hydrogel’s removal performance was studied, and hydrogel with 19.5% EDGE content was determined to be the most effective one with 99% Congo Red removal, at optimal conditions (contact time of 7 h, dye with concentration, at 50 mg/L, and pH = 7). Swelling ratio, contact time, impact of pH, and dosage rate of hydrogel were investigated. Based on the results, the swelling ratio decreased with an increase in ethylene glycol diglycidyl ether, while the efficiency of removal of Congo Red improved as dosage amount was increased. Regarding heavy metal ion removal, Pb²⁺ and Zn²⁺ ions were considered in this study, where results showed that the maximum adsorption capacity for Pb²⁺ (383.96 mg/g) was observed in hydrogel with 19.5% EDGE, while this was 244.12 mg/g for Zn²⁺, demonstrating higher selectivity for Pb²⁺. This research highlighted the potential of PET-based hydrogels as effective adsorbent material in treatment methods of industrial wastewater simultaneously with plastic waste recycling.