Ability and adsorption processes of anionic dye by polymer and surfactant-based organoclays

LL Zhang and A Zaoui and W Sekkal, JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY, 151, 251-263 (2025).

DOI: 10.1016/j.jiec.2025.03.051

Clay-based materials are widely used as adsorbents for dye removal, but their effectiveness in capturing anionic dyes from water remains limited. To address their ability in adsorption anionic dyes, montmorillonite (MMT) was modified with biopolymer chitosan (CHT) and surfactant hexadecyltrimethylammonium (HDTMA) cations. This study employs equilibrium and non-equilibrium molecular dynamic methods to investigate the adsorption mechanisms and desorption process of methyl orange (MO) on modified MMT surfaces. The effective condition for MO adsorption at room temperature is achieved when the organic loading exceeds 1CEC of MMT to change the surface charge to be positive. The CHT-MMT surfaces provide abundant hydrogen bonding sites (NH3+) at acidic conditions for interactions with SO3 - groups of MO, while the HDTMA-MMT surfaces provide hydrophobic interactions and large contact areas for MO adsorption. Bonding analysis confirms the structural stability of two organoclays during adsorption. The activation energy of MO desorption from CHT-MMT ranges from 14.39 to 17.91 kJ/mol at low velocities (<= 30 m/s), comparable to that of HDTMA-MMT (16.28 kJ/mol). This suggests that the larger surface roughness provided by HDTMA tails compensates for the weaker interaction mechanisms involved in adsorption, ensuring the adsorption strength of MO. The study demonstrates the ability of positively charged CHT-MMT and HDTMA-MMT for anionic dye uptake, and highlights the potential for use in treating mixed dyes systems in real wastewater. Synopsis: This work provides ideas for developing efficient and economical adsorbents and demonstrates the promising future of clay-based adsorbents for dye adsorption.

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