Adsorption properties of congo red from aqueous solution on modified hectorite: Kinetic and thermodynamic studies

Two modified hectorites have been designed and synthesized by two cationic surfactants namely cetyltrimethyl ammonium bromide (CTAB) and octadecylamine (ODA) for selective removal of the anionic dye congo red (CR) from aqueous solution. The adsorbent capacity of modified hectorites was discussed and the optical contents of CTAB and ODA were 35% and 28%, respectively. Modified hectorites were characterized by X-ray powder diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The effects of adsorbents content and adsorption temperature on the sorption of CR on modified hectorites were studied. Experimental results showed that the equilibrium adsorption data fitted well with the Langmuir isotherm and the adsorption capacities were 182 and 197 mg/g for the modified cetyltrimethyl ammonium bromide hectorite (CTAB-Hect) and ammonium bromide hectorite (ODA-Hect), respectively. Kinetic studies showed that the dynamical data fitted well with the pseudo-second-order kinetic model. For thermodynamic studies, parameters such as the Gibbs free energy (ΔG0), the enthalpy (ΔH0) and the entropy (ΔS0) indicated that the adsorption process was spontaneous and endothermic in nature.