Characterization of EDTA-cross-linked beta-cyclodextrin grafted onto Fe-Al hydroxides as an efficient adsorbent for methylene blue

The synthesis process of Fe-Al hydroxides coated with ethylenediaminetetraacetic acid (EDTA)-cross-linked beta-cyclodextrin polymer (FA-ECD) and its utilization in the adsorption of methylene blue (MB) were investigated. The FA-ECD before and after adsorption was characterized by scanning electron microscopy (SEM), Brunauer-Emmet-Teller (BET) analysis, Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric (TG) analysis, and X-ray diffraction (XRD). In addition, the EDTA and beta-cyclodextrin contents were determined quantitatively. The optimization of several variables such as contact time, pH, initial concentration, and adsorbent dosage achieved the maximum removal percentages in mild conditions. The results revealed that the adsorption process mainly depended on the pH value and the optimal adsorption capacity of the MB was 60.71 mg/g at pH 8. Subsequently, the experimental equilibrium data at different temperatures were fitted with the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models; the Freundlich model provided the best results. In addition, the pseudo-second-order kinetic model best described the adsorption of the MB. The thermodynamic analysis proved that the adsorption process was endothermic and spontaneous. (C) 2018 Elsevier Inc. All rights reserved.