Characterization of Cationic-Nonionic Surfactants Modified Montmorillonite and Its Application for the Removal of p-Nitrophenol

A series of cationic-nonionic surfactants modified montmorillonites (Mt) were prepared by incorporating a mixture of a cationic surfactant cetyl trimethyl ammonium bromide (CTMAB) and a nonionic surfactant octylphenol polyethoxylate (TX-100) to montmorillonite. X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) results showed that the interlayer spacing and organic carbon content of cationic-nonionic surfactants modified montmorillonite were larger than those of Mt modified by individual CTMAB or TX-100 The adsorption of p-nitrophenol onto the as-prepared sample was investigated with respect to contact time, temperature and initial concentration. The adsorption experiments indicated that 110C/90T-Mt had the largest equilibrium adsorption capacity (108.9 mg/g), and the adsorption isotherms of the resulting samples were in good agreement with the Langmuir isotherm. The adsorption kinetics of p-nitrophenol onto the modified Mt samples can be best described by the pseudo-second-order model. Intraparticle diffusion was not the only rate-limiting step. The surface adsorption and intraparticle diffusion were concurrently operating during the p-nitrophenol and the modified sample interaction. The activation energy, change of free energy, enthalpy and entropy of cationic-nonionic modified Mt were also evaluated for the adsorption of p-nitrophenol. Thermodynamic analysis indicated that the adsorption was a spontaneous and endothermic process.