Institute of Environmental Health, Oregon Health and Science University , 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.
School of Environmental and Materials Engineering, Shanghai Second Polytechnic University (SSPU) , Shanghai 201209, People's Republic of China.
Environ Sci Technol. 2015 Sep 1;49(17):10589-97. doi: 10.1021/acs.est.5b02804. Epub 2015 Aug 11.
Nano zerovalent iron synthesized with carboxymethylcelluose (CMC-nZVI) is among the leading formulations of nZVI currently used for in situ groundwater remediation. The main advantage of CMC-nZVI is that it forms stable suspensions, which are relatively mobile in porous media. Rapid contaminant reduction by CMC-nZVI is well documented, but the fate of the CMC-nZVI (including "aging" and "reductant demand") is not well characterized. Improved understanding of CMC-nZVI fate requires methods with greater specificity for Fe(0), less vulnerability to sampling/recovery artifacts, and more practical application in the field. These criteria can be met with a simple and specific colorimetric approach using indigo-5,5'-disulfonate (I2S) as a chemical redox probe (CRP). The measured stoichiometric ratio for reaction between I2S and nZVI is 1.45 ± 0.03, suggesting complete oxidation of nZVI to Fe(III) species. However, near pH 7, reduction of I2S is diagnostic for Fe(0), because aqueous Fe(II) reduces I2S much more slowly than Fe(0). At that pH, adding Fe(II) increased I2S reduction rates by Fe(0), consistent with depassivation of nZVI, but did not affect the stoichiometry. Using the I2S assay to quantify changes in the Fe(0) content of CMC-nZVI, the rate of Fe(0) oxidation by water was found to be orders of magnitude faster than previously reported values for other types of nZVI.
用羧甲基纤维素钠（CMC）合成的纳米零价铁（nZVI）是目前用于原位地下水修复的 nZVI 的主要配方之一。CMC-nZVI 的主要优势在于它能形成稳定的悬浮液，在多孔介质中具有相对较高的迁移性。CMC-nZVI 能快速降低污染物的浓度，这已得到充分证实，但 CMC-nZVI 的命运（包括“老化”和“还原剂需求”）尚未得到很好的描述。要更好地了解 CMC-nZVI 的命运，需要使用对 Fe(0) 具有更高特异性、对采样/回收干扰物的敏感性更低、且在实际应用中更具实用性的方法。这些标准可以通过使用靛红-5,5'-二磺酸钠（I2S）作为化学氧化还原探针（CRP）的简单而特定的比色法来满足。I2S 与 nZVI 之间反应的测量化学计量比为 1.45 ± 0.03，表明 nZVI 完全氧化为 Fe(III)物种。然而，在接近 pH 7 的条件下，I2S 的还原是 Fe(0)的诊断指标，因为水合 Fe(II)还原 I2S 的速度比 Fe(0)慢得多。在该 pH 值下，添加 Fe(II)会增加 Fe(0)还原 I2S 的速率，这与 nZVI 的去钝化一致，但不会影响化学计量比。使用 I2S 测定法来定量 CMC-nZVI 中 Fe(0)含量的变化，发现水对 Fe(0)的氧化速率比以前报道的其他类型 nZVI 快几个数量级。
