Novel modified bentonites applied to the removal of an anionic azo-dye from aqueous solution

Abstract

Clay minerals, such as montmorillonite, have been applied as adsorbents to toxic compound removals from the environment and reduction of pollutants in soil, water and air. Although montmorillonites show better interaction with cationic species, their chemical modification can improve the final adsorptive properties. Therefore, in this work two samples of bentonite (Bentx, x = 1, 2) with distinct cation exchange capacity (80 to 100 cmol (+) Kg−1) reacted with ethylene sulfide (S) and ethylenediamine (en) to obtained organofunctionalized clay solids, which were applied to the removal of Remazol blue RN from aqueous solutions. The solids were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), CHN elemental analysis and thermogravimetry (TG). The basal spacings (d001) of the montmorillonite phase (Mt) changed after reaction with ethylene sulfide from 1.25 nm to 1.49 and 1.43 nm for the Bent1-S and Bent2-S, respectively, indicating the intercalation of the organic molecule in the interlayer spacing of the clay sample, with further decrease of d001 after ethylenediamine intercalation. FTIR spectra confirmed organofunctionalization by the presence of new bands at 2934 and 2855 cm−1, which were attributed to the C–H asymmetric and symmetrical stretchings, respectively. CHN elemental analysis and thermogravimetry indicated a high degree of organofunctionalization. The measured contact angle value of 104-107° suggested the formation of a hydrophobic surface. Adsorption was evaluated at different pH values, adsorbent dosage, reaction time and initial dye concentration conditions. Novel organobentonites showed better dye removal (∼40 mg g−1) than the one achieved by the pristine samples.