Adsorption isotherms of non-ionic surfactants on Na-bentonite (Iran) and evaluation of thermodynamic parameters

Non-ionic surfactants have been adsorbed on bentonite (Iran) as a relatively good adsorbent in various temperatures (297–323 K). The experimental data obtained from non-ionic surfactants on bentonite have been fitted into the adsorption isotherm equations such as: Langmuir, Freundlich, Langmuir–Freundlich (Modified Langmuir), Hill, Redlich–Peterson, BET, Halsey, Harkins–Jura, Smith, Henderson, Chaung-Pfost, Oswin, and some modified forms of these isotherms, and their goodness of fit have been compared. In addition, the data has been fitted into the Modified BET isotherm which considers the dependency of sorption on the temperature. The correlation coefficient (r2) obtained by fitting the experimental data to the Modified Langmuir, Hill, Redlich–Peterson, BET and Modified BET isotherms have been favorably high. The thermodynamic data of Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) terms have been determined for the non-ionic surfactant adsorption; the negative values of ΔG° obtained indicates that the non-ionic surfactant adsorption process is a spontaneous one. Finally, the intercalation of surfactant in the interlamellar space was followed by X-ray measurements.