X-ray Photoelectron Spectroscopy of Fast-Frozen Hematite Colloids in Aqueous Solutions. 5. Halide Ion (F鈥?/sup>, Cl鈥?/sup>, Br鈥?/sup>, I鈥?/sup>) Adsorption

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• 作者：Kenichi Shimizu ; Andrey Shchukarev ; Philipp A. Kozin ; Jean-Fran莽ois Boily
• 刊名：Langmuir
• 出版年：2013
• 出版时间：February 26, 2013
• 年：2013
• 卷：29
• 期：8
• 页码：2623-2630
• 全文大小：353K
• 年卷期：v.29,no.8(February 26, 2013)
• ISSN：1520-5827

文摘

Halide anion (F^{鈥?/sup>, Cl鈥?/sup>, Br鈥?/sup>, and I鈥?/sup>) adsorption and its impact on sodium adsorption at the hematite/water interface were studied by cryogenic X-ray photoelectron spectroscopy (XPS). Measurements were carried out on frozen, centrifuged wet hematite pastes that were previously equilibrated in 50 mM electrolytic solutions in the pH 2鈥?1 range. XPS-derived halide ion surface loadings decreased in the order F鈥?/sup> > I鈥?/sup> 鈮?Cl鈥?/sup> > Br鈥?/sup>, whereas sodium loadings were in the order Na(F) > Na(I) > Na(Br) > Na(Cl). The greater sodium loadings in NaF and in NaI resulted from larger anion loadings in these systems. Bromide ion had the lowest loading among all halide ions despite having a charge-to-size ratio that is intermediate between those of Cl鈥?/sup> and I鈥?/sup>. This unexpected result may have arisen from specific properties of the hematite/water interface, such as water structure and electric double layer thickness. Fluoride ion adsorption proceeded via the formation of hydrogen bonds with the surface hydroxo groups (e.g., 鈮e鈥揙H₂路路路F鈥?/sup> or 鈮e鈥揙H路路路F鈥?/sup>). Surface-bound fluoride ions exert a greater charge-screening effect than the other halide anions, as demonstrated by considerably small zeta potential values. Fe鈥揊 bond formation was excluded as a possible interfacial process as the F 1s peak binding energy (684.2 eV) was more comparable to that of NaF (684.6 eV) than FeF₃ (685.4 eV). Overall, these findings motivate further refinements of existing thermodynamic adsorption models for predicting the ionic composition of hematite particle surfaces contacted with sodium halide aqueous solutions.}