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<p>The development of low-cost and sustainable adsorbents for cationic dye removal remains a significant challenge in wastewater treatment. In this study, raw peanut shells (RPS) were chemically activated using NaOH to produce alkali-activated peanut shells (APS) with enhanced surface and adsorption properties toward methylene blue dye. Alkali treatment induced a mass loss of 33.61% due to the partial removal of hemicellulose, lignin, and mineral components, leading to an increase in specific surface area from 74.17 to 107.34 m<sup>2</sup>/g and greater exposure of oxygen-containing functional groups, as confirmed by FTIR and SEM analyses. Adsorption experiments showed that equilibrium was reached within 90&#xa0;min at pH 8. Kinetic data followed the pseudo-second&#xa0;order model (R<sup>2</sup> = 0.999), indicating that the adsorption process is governed by surface interactions. Equilibrium data were best described by the Langmuir isotherm, with maximum adsorption capacities of 30.3&#xa0;mg/g for RPS and 43.85&#xa0;mg/g for APS. Thermodynamic parameters (ΔG° =  − 3.25 to − 5.90&#xa0;kJ/mol, ΔH° = 36.16&#xa0;kJ/mol) revealed that the adsorption is spontaneous and endothermic. Combined kinetic, isotherm, thermodynamic, FTIR and SEM analyses indicate that methylene blue removal occurs predominantly through physisorption mechanisms involving electrostatic attraction, hydrogen bonding, and π–π interactions. The results demonstrate that NaOH activation significantly enhances the adsorption performance of peanut shells, suggesting that APS could be an efficient, eco-friendly, and low-cost adsorbent in aqueous systems.</p>

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Adsorption mechanisms of methylene blue on alkali-activated peanut shells: kinetic, isotherm, and thermodynamic studies

  • 期刊论文

  • 发表日期：

    2026年5月14日

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  • Laid Zeghoud,
  • Bachir Ben Seghir,
  • Ilham Ben Amor,
  • Messaoud Gouamid,
  • MarouaGdoura Ben Amor,
  • Hanen Sellami,
  • Amina Aichour,
  • Hakim Djafer Khodja

摘要

The development of low-cost and sustainable adsorbents for cationic dye removal remains a significant challenge in wastewater treatment. In this study, raw peanut shells (RPS) were chemically activated using NaOH to produce alkali-activated peanut shells (APS) with enhanced surface and adsorption properties toward methylene blue dye. Alkali treatment induced a mass loss of 33.61% due to the partial removal of hemicellulose, lignin, and mineral components, leading to an increase in specific surface area from 74.17 to 107.34 m2/g and greater exposure of oxygen-containing functional groups, as confirmed by FTIR and SEM analyses. Adsorption experiments showed that equilibrium was reached within 90 min at pH 8. Kinetic data followed the pseudo-second order model (R2 = 0.999), indicating that the adsorption process is governed by surface interactions. Equilibrium data were best described by the Langmuir isotherm, with maximum adsorption capacities of 30.3 mg/g for RPS and 43.85 mg/g for APS. Thermodynamic parameters (ΔG° =  − 3.25 to − 5.90 kJ/mol, ΔH° = 36.16 kJ/mol) revealed that the adsorption is spontaneous and endothermic. Combined kinetic, isotherm, thermodynamic, FTIR and SEM analyses indicate that methylene blue removal occurs predominantly through physisorption mechanisms involving electrostatic attraction, hydrogen bonding, and π–π interactions. The results demonstrate that NaOH activation significantly enhances the adsorption performance of peanut shells, suggesting that APS could be an efficient, eco-friendly, and low-cost adsorbent in aqueous systems.