Formation of Green Rust Sulfate: A Combined in Situ Time-Resolved X-ray Scattering and Electrochemical Study

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• 作者：Imad A. M. Ahmed ; Liane G. Benning ; Gabriella Kakonyi ; Aryani D. Sumoondur ; Nick J. Terrill ; Samuel Shaw
• 刊名：Langmuir
• 出版年：2010
• 出版时间：May 4, 2010
• 年：2010
• 卷：26
• 期：9
• 页码：6593-6603
• 全文大小：1303K
• 年卷期：v.26,no.9(May 4, 2010)
• ISSN：1520-5827

文摘

The mechanism of green rust sulfate (GR-SOb>4b>) formation was determined using a novel in situ approach combining time-resolved synchrotron-based wide-angle X-ray scattering (WAXS) with highly controlled chemical synthesis and electrochemical (i.e., Eh and pH) monitoring of the reaction. Using this approach,GR-SOb>4b> was synthesized under strictly anaerobic conditions by coprecipitation from solutions with known Fe^II/Fe^III ratios (i.e., 1.28 and 2) via the controlled increase of pH. The reaction in both systems proceeded via a three-stage precipitation and transformation reaction. During the first stage,schwertmannite (Feb>8b>Ob>8b>(OH)b>4.5b>(SOb>4b>)b>1.75b>) precipitated directly from solution at pH 2.8−4.5. With increasing pH (>5), Fe²⁺ ions adsorb to the surface of schwertmannite and catalyze its transformation to goethite (α-FeOOH) during the second stage of the reaction. In the third stage, the hydrolysis of the adsorbed Fe²⁺ ions on goethite initiates its transformation to GR-SOb>4b> at pH >7. The GR-SOb>4b> then continues to crystallize up to pH 8.5. These results suggest that with an Fe^II/Fe^III ratio of ≤2 in the initial solution the structural Fe^II/Fe^III of the GR-SOb>4b> will be close to that of the starting composition.