Al-substitution-induced defect sites enhance adsorption of Pb2+ on hematite. Issue 5 (1st April 2019)

• Record Type: Journal Article
• Authors: Liang, Yu; Wang, Mingxia; Xiong, Juan; Hou, Jingtao; Wang, Xiaoming; Tan, Wenfeng
• Is Part Of: Environmental science. Volume 6:Issue 5(2019)
• Page Start: 1323
• Page End: 1331
• Publication Date: 2019-04-01
• Subjects: Environmental sciences -- Periodicals; Nanotechnology -- Periodicals; 620.505
• DOI: 10.1039/c8en01221k
• Languages: English
• ISSNs: 2051-8153

Abstract

Abstract : Al-substitution induces Fe vacancies on hematite (001) facets, which contributes substantially to increase the surface reactivity of hematite. 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 Pb 2+ 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 (FeOH −0.5 ) and triply (Fe3 O −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 Pb 2+ 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 Pb 2+ adsorption capacity of hematite.