Recycled PET/Sepiolite Composite Adsorbent for Methylene Blue Removal: Formulation, RSM Optimisation, Reusability, and Adsorption Mechanism
- 1Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia (UTM), Johor Bahru 81310, Johor, Malaysia
- 2Interdisciplinary Research Centre for Advanced Materials, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia
- 3Department of Chemical Engineering, College of Engineering, King Faisal University, P.O. Box 400, Al Ahsa 31982, Saudi Arabia
Abstract
This study explores the valorisation of post-industrial recycled polyethylene terephthalate (rPET) via incorporation of sepiolite clay to develop a composite adsorbent for methylene blue (MB) dye removal. The composite formulation was evaluated by varying the rPET concentration, TFA:DCM solvent ratio, sepiolite content, and blending time. The selected formulation had an average particle size of 267.10 nm, a specific surface area of 0.67 m2/g, and a pore volume of 0.003925 cm3/g. Adsorption conditions were then optimised using a five-factor, three-level Box–Behnken design, considering contact time, MB concentration, adsorbent dosage, pH, and temperature. The resulting quadratic model was statistically significant (F = 114.18, p < 0.0001), with R2 = 0.9892, adjusted R2 = 0.9805, and predicted R2 = 0.9568; however, the lack-of-fit was also significant (F = 90.90, p < 0.0001), indicating that model predictions should be interpreted within the investigated factor ranges. At the selected conditions of 62.5 min, 25.5 mg/L MB, 2.55 g/50 mL adsorbent, pH 7, and 55 °C, the model predicted an MB removal efficiency of 99.03%. The adsorbent retained at least 93% reusability efficiency after six adsorption–washing–reuse cycles. The kinetic data were described more closely by the pseudo-second-order model, whereas the Freundlich model provided a better representation of the equilibrium data (R2 = 0.9976). Thermodynamic results indicated that adsorption was favourable and exothermic within the investigated temperature range. Overall, the results show that post-industrial PET can be converted into a value-added sepiolite-containing adsorbent for MB removal.
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BibTeX
@article{din2026recycled,
title = {{Recycled PET/Sepiolite Composite Adsorbent for Methylene Blue Removal: Formulation, RSM Optimisation, Reusability, and Adsorption Mechanism}},
author = {Suria Fatin Mohd Din and Zahid Iqbal Khan and Mohammed E. Ali Mohsin and Suleiman Mousa and Norhayani Othman and Mohammad Yousaf Younes and Zurina Mohamad and SK Safdar Hossain},
journal = {International Journal of Molecular Sciences},
year = {2026},
month = oct,
doi = {10.3390/ijms27198841},
url = {https://www.mdpi.com/1422-0067/27/19/8841},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Recycled PET/Sepiolite Composite Adsorbent for Methylene Blue Removal: Formulation, RSM Optimisation, Reusability, and Adsorption Mechanism
AU - Suria Fatin Mohd Din
AU - Zahid Iqbal Khan
AU - Mohammed E. Ali Mohsin
AU - Suleiman Mousa
AU - Norhayani Othman
AU - Mohammad Yousaf Younes
AU - Zurina Mohamad
AU - SK Safdar Hossain
PY - 2026
DA - 2026/10/03
JO - International Journal of Molecular Sciences
DO - 10.3390/ijms27198841
UR - https://www.mdpi.com/1422-0067/27/19/8841
AB - This study explores the valorisation of post-industrial recycled polyethylene terephthalate (rPET) via incorporation of sepiolite clay to develop a composite adsorbent for methylene blue (MB) dye removal. The composite formulation was evaluated by varying the rPET concentration, TFA:DCM solvent ratio, sepiolite content, and blending time. The selected formulation had an average particle size of 267.10 nm, a specific surface area of 0.67 m2/g, and a pore volume of 0.003925 cm3/g. Adsorption conditions were then optimised using a five-factor, three-level Box–Behnken design, considering contact time, MB concentration, adsorbent dosage, pH, and temperature. The resulting quadratic model was statistically significant (F = 114.18, p < 0.0001), with R2 = 0.9892, adjusted R2 = 0.9805, and predicted R2 = 0.9568; however, the lack-of-fit was also significant (F = 90.90, p < 0.0001), indicating that model predictions should be interpreted within the investigated factor ranges. At the selected conditions of 62.5 min, 25.5 mg/L MB, 2.55 g/50 mL adsorbent, pH 7, and 55 °C, the model predicted an MB removal efficiency of 99.03%. The adsorbent retained at least 93% reusability efficiency after six adsorption–washing–reuse cycles. The kinetic data were described more closely by the pseudo-second-order model, whereas the Freundlich model provided a better representation of the equilibrium data (R2 = 0.9976). Thermodynamic results indicated that adsorption was favourable and exothermic within the investigated temperature range. Overall, the results show that post-industrial PET can be converted into a value-added sepiolite-containing adsorbent for MB removal.
SN - 1422-0067
ER -