Resolving Early Stages of Homogeneous Iron(III) Oxyhydroxide Formation from Iron(III) Nitrate Solutions at pH 3 Using Time-Resolved SAXS

详细信息    查看全文

• 作者：Andrew L. Rose ; Mark W. Bligh ; Richard N. Collins ; T. David Waite
• 刊名：Langmuir
• 出版年：2014
• 出版时间：April 1, 2014
• 年：2014
• 卷：30
• 期：12
• 页码：3548-3556
• 全文大小：386K
• 年卷期：v.30,no.12(April 1, 2014)
• ISSN：1520-5827

文摘

Small angle X-ray scattering (SAXS) measurements coupled to a stopped-flow device has permitted the observation of the kinetics of Fe(III) oxyhydroxide (FeOx) formation and transformation from around 1 s to 30 min after initiation under environmentally relevant conditions at pH 3. The Unified Model approach was used to determine the evolution of multiple key parameters (particle scattering mass, mean particle volume, particle concentration, particle dimensionality, and particle size) for two separate structural levels as a function of time, with the results obtained enabling clarification of the mechanisms underlying FeOx formation and transformation under these conditions. Colloidal primary particles (radius of gyration 2鈥?0 nm) that were observable by SAXS formed within 1 s of stopping the flow and subsequently grew over several minutes, first by cluster鈥揷luster addition and then by a monomer-addition mechanism. Aggregation of these primary particles via a secondary cluster鈥揷luster addition mechanism simultaneously resulted in a distinct population of larger (25鈥?0 nm radius of gyration) secondary particles. The primary particles evolved into compact spheroidal forms with fractally rough surfaces, while the secondary particles were relatively open mass fractal structures. Comparison of the observed rates of these processes with those predicted for Fe polymerization indicates that kinetics of primary particle formation were likely controlled initially by rates of exchange between water molecules coordinated with Fe and those in the bulk solution. These findings provide new insights into the mechanisms underlying FeOx formation and transformation, and the kinetics of these mechanisms, at pH 3.