Applied Chemical Engineering

Comparative study of the surface modification of chitosan using anionic surfactants for methylene blue adsorption

Aya B. Mohsin

Department of Chemical Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq

Muthanna J. Ahmed

Department of Chemical Engineering, College of Engineering, University of Baghdad, Baghdad, Iraq

DOI: https://doi.org/10.59429/ace.v9i3.6132

Keywords: methylene blue; anionic surfactant; surface modification; adsorption isotherm; kinetics

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Abstract

Chitosan (CS) hydrogel beads were prepared by dropwise precipitation and surface-modified with three anionic surfactants—sodium dodecyl sulfonate (SDOS), sodium dodecyl sulfate (SDS), and sodium dodecylbenzene sulfonate (SDBS)—to improve methylene blue (MB) removal from water. FTIR and FE-SEM provided qualitative evidence of surface modification and increased surface roughness while indicating retention of the principal chitosan framework. The modified beads exhibited low BET surface areas (7.48–9.63 m² g⁻¹), and the surface-area order did not correspond to MB uptake, suggesting that surface chemistry and the accessibility of surfactant-derived anionic sites were more important than physical area alone. Triplicate batch experiments identified an optimum surfactant modification concentration of 3.0 g L⁻¹ and an optimum solution pH of 6. Adsorption performance followed the order CS/SDOS > CS/SDS > CS/SDBS, with the highest experimentally achieved capacities of 418.60, 390.80, and 275.00 mg g⁻¹, respectively. Equilibrium was reached after approximately 240, 360, and 480 min, respectively. The pseudo-second-order model provided the best statistical description of the kinetic data (R² ≥ 0.995), whereas the Sips model best represented the equilibrium data, indicating greater energetic heterogeneity for CS/SDOS and CS/SDS and near-Langmuir behavior for CS/SDBS. For CS/SDOS, MB removal decreased from approximately 95% for the fresh adsorbent to 52% after the first regeneration and 21% after the fifth regeneration with 0.1 M HCl, demonstrating limited reusability under the tested conditions. Future work should quantify surfactant loading and surface charge and evaluate milder regeneration media to improve adsorbent stability.

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