Repurposing waste plastic into a sustainable adsorbent for removing synthetic dye: experimental, optimization and theoretical modeling

Abstract

initial dye concentration, pH 7, 0.1 g adsorbent dose, 298 K, and 120 min contact time, the material achieved a removal efficiency of 99.3%. Adsorption followed pseudo-second-order kinetics and was fitted both Langmuir and Freundlich isotherm models, indicating combined physical and chemical interactions. Thermodynamic parameters revealed a spontaneous and endothermic process, while regeneration tests demonstrated excellent stability over five cycles. Density functional theory (DFT) analysis indicated that preferential adsorption occur through π-π stacking and donor-acceptor interactions. Box-Behnken design (BBD) optimization further validated the model's predictive accuracy. Overall, this work provides both dual environmental benefits by transforming PET waste into a cost-effective, and eco-friendly adsorbent for sustainable dye removal and water purification.