Adsorption of Methylene Blue onto nano SBA-15 mesoporous material from aqueous media: kinetics, isotherms and thermodynamic studies

Santa Barbara Amorphous (SBA-15) molecular sieve was prepared by hydrothermal synthesis method. The surface and pore structure of SBA-15 were characterized by low-temperature N-2 adsorption isotherm, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Methylene blue dye solution was adsorbed by the synthetic SBA-15, the best adsorption condition and the maximum adsorption capacity of methylene blue by SBA-15 were obtained by experiments, and the maximum adsorption capacity is 223 mg g(-1). The kinetics of the adsorption of methylene blue by SBA-15 was in accordance with the quasi-second-order kinetic equation. The results were analyzed by Langmuir and Freundlich adsorption isotherm model, and the adsorption of methylene blue on SBA-15 was in accord with the Freundlich adsorption isotherm model. The Gibbs free energy changes during the adsorption Delta G degrees < 0 can judge that the adsorption process is spontaneous. The enthalpy change in the adsorption process is -16.623 kJ mol(-1), that is Delta H degrees < 0, indicating that the adsorption process is an exothermic reaction. The negative value of entropy indicates that the adsorption process is a process of entropy reduction. The composite materials after adsorption were characterized by powder XRD, SEM, FT-IR spectra, low temperature N-2 adsorption-desorption. The characterization results show that the composite materials still retained the skeleton structure of the mesoporous materials, but the order degree of the composites was decreased. After adsorption, the average pore size, total pore volume and specific surface area of the composite materials are lower than those of the mesoporous materials before adsorption, indicating that the pores of mesoporous materials were partly filled and blocked. This indicated that the dye molecules were contained in the mesoporous channels.