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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Quantification of rapid environmental redox processes with quick-scanning x-ray absorption spectroscopy (Q-XAS)
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Quantification of rapid environmental redox processes with quick-scanning x-ray absorption spectroscopy (Q-XAS)

机译：使用快速扫描X射线吸收光谱仪（Q-XAS）量化快速环境氧化还原过程

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摘要

Quantification of the initial rates of environmental reactions at the mineral/water interface is a fundamental prerequisite to determining reaction mechanisms and contaminant transport modeling and predicting environmental risk. Until recently, experimental techniques with adequate time resolution and elemental sensitivity to measure initial rates of the wide variety of environmental reactions were quite limited. Techniques such as electron paramagnetic resonance and Fourier transform infrared spectroscopies suffer from limited elemental specificity and poor sensitivity to inorganic elements, respectively. Ex situ analysis of batch and stirred-flow systems provides high elemental sensitivity; however, their time resolution is inadequate to characterize rapid environmental reactions. Here we apply quick-scanning x-ray absorption spectroscopy (Q-XAS), at sub-second time-scales, to measure the initial oxidation rate of As(III) to As(V) by hydrous manganese(IV) oxide. Using Q-XAS, As(III) and As(V) concentrations were determined every 0.98 s in batch reactions. The initial apparent As(III) depletion rate constants (t < 30 s) measured with Q-XAS are nearly twice as large as rate constants measured with traditional analytical techniques. Our results demonstrate the importance of developing analytical techniques capable of analyzing environmental reactions on the same time scale as they occur. Given the high sensitivity, elemental specificity, and time resolution of Q-XAS, it has many potential applications. They could include measuring not only redox reactions but also dissolution/precipitation reactions, such as the formation and/or reductive dissolution of Fe(III) (hydroxides, solid-phase transformations (i.e., formation of layered-double hydroxide minerals), or almost any other reaction occurring in aqueous media that can be measured using x-ray absorption spectroscopy.
机译：矿物质/水界面的环境反应初始速率的量化是确定反应机理和污染物迁移模型并预测环境风险的基本前提。直到最近，具有足够的时间分辨率和元素敏感性来测量各种环境反应的初始速率的实验技术还是十分有限的。电子顺磁共振和傅立叶变换红外光谱等技术分别具有局限的元素特异性和对无机元素的敏感性。间歇和搅拌流系统的异位分析可提供高元素灵敏度；然而，它们的时间分辨率不足以表征快速的环境反应。在这里，我们在亚秒级的时间尺度上应用快速扫描X射线吸收光谱（Q-XAS），以测量含水锰（IV）氧化物将As（III）转化为As（V）的初始氧化速率。使用Q-XAS，分批反应中每0.98 s测定一次As（III）和As（V）的浓度。 Q-XAS测得的初始表观As（III）耗尽速率常数（t <30 s）几乎是传统分析技术测得的速率常数的两倍。我们的结果表明，开发能够在与环境反应相同的时间尺度上进行分析的分析技术的重要性。鉴于Q-XAS的高灵敏度，元素特异性和时间分辨率，它具有许多潜在的应用。它们不仅可以测量氧化还原反应，还可以测量溶解/沉淀反应，例如Fe（III）的形成和/或还原溶解（氢氧化物，固相转变（即，层状双氢氧化物矿物的形成））或几乎可以使用X射线吸收光谱法测量的在水性介质中发生的任何其他反应。

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