Adsorption of methylene blue on imine modified sepiolite from aqueous solutions

Abstract

In this study, a modified sepiolite for methylene blue (MB) adsorption was designed. Modification of sepiolite was performed using N,N-dimethy1-4-(((3-(triethoxysilyl)propyl)imino)methyl)aniline (MESPIA) in the presence of ethanol solution. The modified sepiolite (SP-MESPIA) was characterized by using Fourier-transform infrared spectroscopy-at-tenuated total reflectance, scanning electron microscopy, thermal gravimetric analysis and Brunauer-Emmett-Teller instruments. The amount of adsorbed MB was measured by UV-Vis spectroscopy. The effects of concentration, temperature, ionic strength and pH to the adsorption capacity of SP-MESPIA were investigated. It was determined that chemical bonding took place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and the silane group of MESPIA by releasing the ethoxy groups to the solvent. Sepiolite degraded in four steps, while modified sepiolite degraded in three steps and at higher temperatures. The adsorption capacity of modified sepiolite increased with increasing pH, temperature, ionic strength. The experimental data were analyzed using the Langmuir and. Freundlich adsorption models. The experimental data fitted very well with Langmuir isotherm equation. The Langmuir monolayer capacity changed in the range of 32.9 10(-5)-56.7 10(-5)mol/g. The adsorption of MB was endothermic in nature (Delta H: 120 kJ/mol) and accompanied by an increase in entropy (AS: 513 J/molK) and a decrease in Gibbs energy (Delta G: 35.53 to 45.79 kJ/mol in the temperature range of 30-50 degrees C).