Fluoride adsorption on an Fe–Al–Ce trimetal hydrous oxide: Characterization of adsorption sites and adsorbed fluorine complex species
2013
Wu, Xiaomei | Zhang, Yu | Dou, Xiaomin | Zhao, Bei | Yang, Min
To better understand fluoride (F) adsorption mechanisms of metal oxide-based adsorbent, a previously developed iron–aluminum–cerium hydroxide (Fe–Al–Ce) adsorbent with a high adsorption capacity for F was investigated using various spectroscopic methods including X-ray photoelectron spectroscopy (XPS) and ¹⁹F magic-angle spinning nuclear resonance (¹⁹F MAS NMR). XRD and BET results showed that the Fe–Al–Ce adsorbent maintained an amorphous structure with high specific surface areas and large pore volumes. Deconvolution of XPS O1s peaks showed a quantitative ligand exchange relationship between the metal–hydroxyl (−OH) groups and F ions. Deconvolution of XPS F1s peaks showed that the F ions were able to substitute for all three metal–OH groups. Ce–OH was the preferential adsorption site at low F load (10mgg⁻¹), while Al–F became the most abundant complex species with increasing F loads (80 and 138mgg⁻¹). Three types of complex species (Al₃–F, Ceₓ–Fy and Feₓ–Fy) were identified by ¹⁹F MAS NMR analysis under 20 and 80mgg⁻¹ F loads. AlF₃ was suggested as the dominant specie at a high F load (138mgg⁻¹) by both of ¹⁹F MAS NMR and XRD analysis.
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