Modification of montmorillonite by Gemini surfactants with different chain lengths and its adsorption behavior for methyl orange

Abstract To investigate the effect of the alkyl chain length of Gemini surfactants on the adsorption behavior of corresponding organoclays for azo dye methyl orange (MO) removal in aqueous solution, they were prepared by modifying Na-montmorillonite (Na-Mt) using a series of commercialized Gemini surfactants, [C12H25-N+(CH3)2-CH2]2·2Br− (G12-2-12), [C16H33-N+(CH3)2-CH2]2·2Br− (G16-2-16), and [C18H37-N+(CH3)2-CH2]2·2Br− (G18-2-18), which were characterized by identical spacer chain length and different alkyl chain lengths. The structure, morphology and surface properties of organoclays were characterized via XRD, FTIR, TG, SEM, and water contact angle. The results revealed that the interlayer space, hydrophobicity, and dispersibility of organoclays increased significantly with increasing the alkyl chain length of the Gemini surfactants. The adsorption behavior of MO from aqueous solution onto the organoclays was determined. The results indicated that the adsorption capacity of the organoclays was in the order: G16-2-16-Mt > G18-2-18-Mt > G12-2-12-Mt. The highest adsorption capacity of G16-2-16-Mt can be reasonably attributed to the suitable interlayer space, hydrophobicity, and interlayer packing density of the surfactants of G16-2-16-Mt. Moreover, the effects of the pH of the MO solution, adsorption temperature, contact time and the initial MO concentration on the adsorption capacity of MO on Gemini surfactant-modified Mt was also investigated. The adsorption capacity of G16-2-16-Mt decreased with increasing pH and exhibited a maximum at 30 °C. The adsorption isotherms of MO onto G16-2-16-Mt and G18-2-18-Mt were in good agreement with the Langmuir equation, and the adsorption kinetics can best be described by a pseudo-first-order model.