The removal of p-nitrophenol from aqueous solutions by adsorption using gemini surfactants modified montmorillonites

Montmorillonites modified by two gemini surfactants (1,3-bis(dodecyldimethylammonio)-propane dibromide (BDP) and 1,3-bis(dodecyldimethylammonio)-2-hydroxypropane dichloride (BDHP)) via ion exchange were used to remove p-nitrophenol (PNP) from aqueous solutions. The organo-montmorillonites were characterized by X-ray diffraction (XRD) and FT-IR spectroscopy. The effects of the concentration of modified agent, adsorbent mass, pH and contact time were investigated in detail. The results showed that as the concentration of modified agent increased, the adsorption amount increased accordingly and reached maximum adsorption when the concentration of modified agent approached and exceeded 1.0CEC. The removal percentages of PNP increased with the increasing of adsorbent mass at constant initial PNP concentration (100 mg/L). The results revealed that the adsorption of PNP increases with an increase in pH. The adsorption kinetics was found to follow the pseudo-second-order kinetic model and the equilibrium data fitted the Langmuir, Redlich-Peterson and Temkin equations better than Freundlich equation for both BDP modified montmorillonite (BDP-Mt) and BDHP modified montmorillonite (BDHP-Mt). The results also showed that BDHP-Mt containing one hydroxyl in the gemini surfactant molecule was more effective than BDP-Mt for the sorption of PNP from aqueous solutions. Thus, a new idea was provided for the selection of high efficient modified agent, i.e., hydroxyl-containing gemini surfactants. The negative values of AG and AN obtained from thermodynamic study of adsorption process indicated the spontaneous and exothermic nature of the two processes. (C) 2012 Elsevier B.V. All rights reserved.