Synthesis and Characterization of Mixed-Valent Iron Layered Double Hydroxides (“Green Rust”),ACS Earth and Space Chemistry

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Synthesis and Characterization of Mixed-Valent Iron Layered Double Hydroxides (“Green Rust”)
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-12-19 , DOI: 10.1021/acsearthspacechem.0c00272
Vincent P. Aguirre ₁ , Simonne Jocic ₁ , Paul Webster ₁ , Christopher Buser ₁ , John A. Moss ₁ , Laura M. Barge ₂ , Yijie Tang ₃ , Yisong Guo ₃ , Marc M. Baum ₁

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Mixed-valent iron-layered double hydroxides (LDHs), also known as “green rust” (GR), are increasingly becoming recognized as important chemically reduced minerals. GR is believed to have contributed to the accumulation of biomolecules in primordial oceans and to have played a role in the geochemical cycles of early Earth and Mars. The high oxygen sensitivity of these LDHs makes them challenging to prepare and study. Consequently, a synthesis is described herein that affords pure GR compounds over a range of Fe(III) mole fractions and with a variety of intercalated anions. Reliable synthesis of pure GR required two key considerations: (1) ensure accurate and controlled pH titrations and (2) rigorously exclude oxygen before, during, and after the target Fe(II)/Fe(III) ratio is achieved. A detailed protocol for the strictly anoxic synthesis, real-time reaction monitoring, product characterization, and transport of a variety of GR samples is described. Protection of the air-sensitive samples from traces of oxygen for postsynthesis measurements or experiments can be challenging, leading to the potential formation of oxidation product impurities. Analysis of GR specimens by electron microscopy with the described methods enables rapid quality control to confirm sample integrity, including elemental microanalysis. The experimental details in the preparation of pure GR samples provide an important foundation to the geochemical community studying this chemically versatile group of compounds.

中文翻译：

混合价铁层状双金属氢氧化物（“绿锈”）的合成与表征

混合价铁层双氢氧化物（LDH），也称为“绿锈”（GR），正日益被认为是重要的化学还原矿物质。人们认为，遗传资源有助于原始海洋中生物分子的积累，并在地球早期和火星的地球化学循环中发挥了作用。这些LDH的高氧敏感性使其难以制备和研究。因此，本文描述了一种合成，该合成提供了在一定范围的Fe（III）摩尔分数范围内和各种嵌入阴离子的纯GR化合物。可靠地合成纯GR需要两个关键考虑因素：（1）确保准确和受控的pH滴定，以及（2）在达到目标Fe（II）/ Fe（III）比之前，期间和之后严格排除氧气。严格缺氧合成的详细协议，描述了实时反应监测，产物表征以及各种GR样品的运输。保护空气敏感的样品免受痕量氧气的影响，以进行合成后的测量或实验可能具有挑战性，导致潜在形成氧化产物杂质。用上述方法通过电子显微镜对GR样品进行分析，可以快速进行质量控制，以确认样品的完整性，包括元素显微分析。纯GR样品制备中的实验细节为地球化学界研究这一化学上通用的化合物组提供了重要基础。保护空气敏感的样品免受痕量氧气的影响，以进行合成后的测量或实验可能具有挑战性，导致潜在形成氧化产物杂质。用上述方法通过电子显微镜对GR样品进行分析，可以快速进行质量控制，以确认样品的完整性，包括元素显微分析。纯GR样品制备中的实验细节为地球化学界研究这一具有化学多样性的化合物组提供了重要基础。保护空气敏感的样品免受痕量氧气的影响，以进行合成后的测量或实验可能具有挑战性，导致潜在形成氧化产物杂质。用上述方法通过电子显微镜对GR样品进行分析，可以快速进行质量控制，以确认样品的完整性，包括元素显微分析。纯GR样品制备中的实验细节为地球化学界研究这一化学上通用的化合物组提供了重要基础。

更新日期：2021-01-21

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