Characterization and Adsorption Properties of Chemically Modified Sepiolite

Abstract

Modification of sepiolite clay has been performed using triethoxy-3-(2-imidazolin-1-yl)propylsilane in the presence of toluene solution. The modified material was characterized by FTIR spectroscopy, XRD, and simultaneous DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of sepiolite and the silane group of the triethoxy-3-(2-imidazolin-1-yl)propylsilane by releasing the ethoxy groups to the solvent. Thermal decomposition of natural and modified sepiolites was carried out with a thermogravimetric analyzer. In TG and DTA analysis, during gradual heating in an oxidizing atmosphere, the modified sepiolite was oxidized, giving rise to significant exothermic peaks. The exothermic peak in the temperature range of 200−650 °C depended on the modifier loading and provided evidence of bond formation on the sepiolite surface. For natural sepiolite, a mass loss of 20.43% was observed up to 900 °C, whereas this value increased to 31.90% for modified sepiolite under oxygen atmosphere. Electrokinetic properties of the modified-sepiolite suspensions were also examined as a function of the initial electrolyte concentration and equilibrium pH using a Zeta Meter 3.0 instrument. To determine the adsorption capacity of modified sepiolite for metal ions, the experiments were examined as a function of pH, ionic strength, and temperature. The adsorption capacity of modified sepiolite increased with increasing pH and temperature, but ionic strength was found to have no significant effect. The experimental data were analyzed using the Langmuir and Freundlich adsorption models. Satisfactory agreement between the metal uptake capacities by the modified sepiolite was expressed in terms of the correlation coefficient (R2). The Langmuir model represented the sorption process better than the Freundlich model, with R2 values ranging from 0.9603 to 0.9977.