Division of Environmental and Biomolecular Systems, Oregon Health & Science University, Portland, OR 97006, USA.
Environ Sci Technol. 2011 Feb 15;45(4):1586-92. doi: 10.1021/es103185t. Epub 2011 Jan 4.
Oxidation-reduction potential (ORP) measurements have been widely used to assess the results of injection of nano zerovalent iron (nZVI) for groundwater remediation, but the significance of these measurements has never been established. Using rotating disk electrodes (RDE) in suspensions of nZVI, we found the electrode response to be highly complex but also a very sensitive probe for a range of fundamentally significant processes. The time dependence of the electrode response reflects both a primary effect (attachment of nZVI onto the electrode surface) and several secondary effects (esp., oxidation of iron and variations in dissolved H2 concentration). At nZVI concentrations above ∼200 mg/L, attachment of nZVI to the electrode is sufficient to give it the electrochemical characteristics of an Fe(0) electrode, making the electrode relatively insensitive to changes in solution chemistry. Lower nZVI concentrations give a proportional response in ORP, but much of this effect is mediated by the secondary effects noted above. Coating the nZVI with natural organic matter (NOM), or the organic polymers used to make stabile suspensions of nZVI, moderates its effect on ORP measurments. Our results provide the basis for interpretating ORP measurements used to characterize the results of injecting nZVI into groundwater.
氧化还原电位（ORP）测量已被广泛用于评估纳米零价铁（nZVI）注入地下水修复的结果，但这些测量的意义从未得到证实。使用旋转圆盘电极（RDE）在 nZVI 的悬浮液中，我们发现电极响应非常复杂，但也是一系列基本重要过程的非常敏感的探针。电极响应的时间依赖性反映了两个主要影响因素（即 nZVI 附着在电极表面上）和几个次要影响因素（例如，铁的氧化和溶解 H2 浓度的变化）。在 nZVI 浓度高于约 200mg/L 时，nZVI 附着在电极上足以使其具有 Fe(0)电极的电化学特性，从而使电极对溶液化学变化相对不敏感。较低浓度的 nZVI 在 ORP 中产生比例响应，但这种效应很大程度上受到上述次要影响的介导。用天然有机物（NOM）或用于制备 nZVI 稳定悬浮液的有机聚合物对 nZVI 进行涂层处理，可以减轻其对 ORP 测量的影响。我们的研究结果为解释用于表征将 nZVI 注入地下水的结果的 ORP 测量提供了依据。
