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Al-substitution-induced defect sites enhance adsorption of Pb2+ on hematite

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Abstract

Al-substitution in hematite is ubiquitous in nature and strongly affects the environmental behaviors of hematite. However, the defect microstructure caused by Al-substitution and its inner relationship with the surface reactivity of hematite remain unclear. In this study, the crystal structure of Al-substituted hematite was characterized by high-resolution electron transmission microscopy (HRTEM) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Acid–base titration and Pb2+ adsorption experiments were performed to investigate the surface reactivity of Al-substituted hematite. HRTEM images revealed that the proportion of (001) facets on hematite increased from 44.0 ± 3.8% to 84.8 ± 6.5% with increasing Al-substitution. HAADF-STEM images indicated that Al-substitution resulted in more vacancies of Fe atoms on hematite (001) facets. At these Fe defect sites, additional singly ([triple bond, length as m-dash]FeOH−0.5) and triply ([triple bond, length as m-dash]Fe3O−0.5) coordinated hydroxyl sites were formed. The weight loss due to dehydrogenation was 1.7%, 3.3% and 6.2% with increasing Al-substitution from 0%, 5% to 10%. Besides, the relative percentage of surface oxygen atoms in the surface hydroxyl sites of Al-substituted hematite was consistent with the results of thermogravimetric analysis. At pH 5, the relative charge density of the hematite with 0%, 5% and 10% Al-substitution was 73, 94 and 241 mC m−2, and their adsorption capacity for Pb2+ was 0.82, 1.23 and 3.51 μmol m−2, respectively. These results indicate that the formation of more defect sites with increasing Al-substitution can significantly enhance the surface charge density and Pb2+ adsorption capacity of hematite.

Graphical abstract: Al-substitution-induced defect sites enhance adsorption of Pb2+ on hematite

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Publication details

The article was received on 30 Oct 2018, accepted on 25 Mar 2019 and first published on 26 Mar 2019


Article type: Paper
DOI: 10.1039/C8EN01221K
Citation: Environ. Sci.: Nano, 2019, Advance Article

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    Al-substitution-induced defect sites enhance adsorption of Pb2+ on hematite

    Y. Liang, M. Wang, J. Xiong, J. Hou, X. Wang and W. Tan, Environ. Sci.: Nano, 2019, Advance Article , DOI: 10.1039/C8EN01221K

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