A comparison of trimeric surfactant intercalated montmorillonite with its gemini modified one: Characterization and application in methyl orange removal

Trimeric surfactant methyldodecylbis [2-(dimethyldodecylammonio)ethyl] ammonium tribromide (3RenQ) and the corresponding dimer 1.2-bis(dodecyldimethylammonio)ethane dibromide (2RenQ), were used to modify sodium montmorillonite. Organo-montmorillonites 3RenQ-Mt and 2RenQ-Mt were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, N2 adsorption isotherms, thermogravimetric analysis (TG), scanning electron microscopy (SEM) and dispersibility measurement. The results showed that 3RenQ and 2RenQ had inserted into the lamella of sodium montmorillonite successfully, the interlayer spacer and the hydrophilicity of organoclays increased with the increasing of the cationic exchange capacity (CEC) of surfactants and polymerization degree. The adsorption experiments of methyl orange (MO) on 3RenQ-Mt and 2RenQ-Mt were studied using batch method as a function of the concentration of surfactants, contact time, pH and temperature. The optimal conditions for MO on 3RenQ-Mt and 2RenQ-Mt were as follows: 1.0 CEC of the concentration of surfactants, contact time of 6 h, natural pH of 3, the temperature of 20 °C, the equilibrium adsorption capacity of 3RenQ-Mt and 2RenQ-Mt reached to 85.97 and 98.07 mg g− 1, respectively; at the same experimental condition, 3RenQ-Mt exhibited the stronger interaction with MO than 2RenQ-Mt. The kinetic data were better described by the pseudo-second order kinetics model. The adsorption isotherm was in good agreement with the Langmuir model. Thermodynamic parameters such as the Gibbs free energy ΔGθ, the standard enthalpy ΔHθ and the standard entropy ΔSθ confirmed that the process of MO adsorption was spontaneous, exothermic, physisorption and randomness decreasing.