Acid-activated chitosan-modified Iranian bentonite for adsorption of Cu(II) and Zn(II) from water; A green and sustainable water treatment approach.

Authors

Sam Daftari, Mojgan Salavati, Manoochehr Mortazavi Chamchali

Published in

PloS one. Volume 21. Issue 7. Pages e0344207. Epub Jul 30, 2026.

Abstract

This study evaluates the adsorption performance of an Iranian bentonite modified through two routes: activation with HNO3 followed by calcination at 500 °C yielding NWF adsorbent and activation with HCl followed by chitosan intercalation to obtain HWF adsorbent. Batch experiments assessed Cu2+ and Zn2+ removal from aqueous solutions under varying pH, contact time (5-45 min), sorbent dosage (10-150 mg), initial concentration (20-200 mg/L), and temperatures (20-45°C). Atomic Absorption Spectroscopy was used to evaluate heavy metal concentrations. Nonlinear isotherm fitting showed that the Langmuir model described the data well with high mass normalized capacities under the low-dose condition. Freundlich fits indicated favorable adsorption on heterogeneous surfaces. Kinetics followed the pseudo-second-order model (R² = 0.996-0.998), could be described by chemisorption and in case of NWF, faster uptake (higher k2) achieved. Optimal adsorption performance occurred at a pH of approximately 6-7, achieving equilibrium capacities (qe) as high as 99.0 mg/g and blank tests at pH ≥ 8 minimized contributions from metal hydroxide precipitation. Thermodynamic analysis has been carried out to confirm spontaneous and endothermic adsorption in temptatures ranged from 20-45°C. X-ray Diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy corroborated successful modification and enhanced site accessibility. The results of this study showed that acid-activated and chitosan-modified bentonites are low-cost, effective, and sustainable sorbents for Cu2+ and Zn2+ removal from water, with practical relevance to wastewater treatment.

PMID:
42531327
Bibliographic data and abstract were imported from PubMed on 31 Jul 2026.

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