Enhanced adsorption of Eu(III) on mesoporous Al2O3/expanded graphite composites investigated by macroscopic and microscopic techniques.

Mesoporous Al(2)O(3) was intercalated into an expanded graphite (EG) interlayer to prepare mesoporous Al(2)O(3)/EG composites. The basal spacing of mesoporous Al(2)O(3)/EG composites was enlarged as compared to raw graphite from the X-ray diffraction analysis. The massive surface functional groups and wedge-shaped pores were observed in terms of potentiometric acid-base titration analysis and scanning electron microscope, respectively. The pH-dependent adsorption of Eu(III) on mesoporous Al(2)O(3)/EG composites was evidently independent of ionic strength. The maximum adsorption capacity of Eu(III) on mesoporous Al(2)O(3)/EG composites at pH 6.0 and T = 293 K was calculated to be 5.14 mg g(-1). Desorption kinetics and cyclic operation results showed that mesoporous Al(2)O(3)/EG composites presented high hydrothermal stability in aqueous solution. The thermodynamic parameters suggested that Eu(III) adsorption on mesoporous Al(2)O(3)/EG composites is an endothermic and a spontaneous process. The decrease of Eu-O bond distance with the increasing pH demonstrated that the adsorption mechanism between Eu(III) and mesoporous Al(2)O(3)/EG composites would shift from outer-sphere surface complexation to inner-sphere surface complexation in terms of extended X-ray absorption fine structure spectroscopy analysis.