State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, No. 68 Jincheng Street, East Lake High-Tech Development Zone, Wuhan 430078, P. R. China.
Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, School of Environmental Studies, China University of Geosciences, No. 68 Jincheng Street, East Lake High-Tech Development Zone, Wuhan 430078, P. R. China.
Environ Sci Technol. 2022 Sep 20;56(18):13408-13418. doi: 10.1021/acs.est.2c01312. Epub 2022 Sep 5.
Hydrogen peroxide (HO) and hydroxyl radical (OH) production during oxygenation of reduced iron (Fe(II)) and natural organic matter (NOM) in the subsurface has been increasingly discovered, whereas the effect of the C/Fe molar ratio in Fe(II) and NOM coexisting systems remains poorly understood. In this study, aqueous Fe(II) and reduced humic acid (HA) mixture at different C/Fe molar ratios (0-20) were oxygenated. Results show that both HO and OH accumulation increased almost linearly with the increase in the C/Fe ratio, with a more prominent increase in OH accumulation at high C/Fe molar ratios. At low C/Fe molar ratios (C/Fe ≤ 1.6), electrons mainly transferred from dissolved inorganic Fe(II), surface-adsorbed Fe(II), and a low proportion of HA-complexed Fe(II) to O; with the increase in the C/Fe ratio to a high level (C/Fe ≥ 5), the main electron source turned to HA-complexed Fe(II) and free HA. The changes in the electron source and electron transfer pathway with the increase in the C/Fe ratio increased the yield of OH relative to HO. This study highlights the important role of the C/Fe ratio in controlling HO and OH production and therefore in accurately evaluating the associated environmental impacts.
在地下环境中，氧气氧化还原态铁（Fe(II)）和天然有机物（NOM）时，会产生过氧化氢（HO）和羟基自由基（OH），而共存的 Fe(II)和 NOM 中 C/Fe 摩尔比的影响仍知之甚少。在这项研究中，在不同的 C/Fe 摩尔比（0-20）下，对水溶液中的 Fe(II)和还原腐殖酸（HA）混合物进行了氧化。结果表明，HO 和 OH 的积累几乎随 C/Fe 比的增加呈线性增加，在高 C/Fe 摩尔比下，OH 的积累增加更为显著。在低 C/Fe 摩尔比（C/Fe≤1.6）下，电子主要从溶解态无机 Fe(II)、表面吸附态 Fe(II)和一小部分与 HA 络合的 Fe(II)转移到 O；随着 C/Fe 比增加到较高水平（C/Fe≥5），主要的电子源转变为与 HA 络合的 Fe(II)和游离 HA。随着 C/Fe 比的增加，电子源和电子转移途径的变化增加了 OH 相对于 HO 的产率。本研究强调了 C/Fe 比在控制 HO 和 OH 产生以及准确评估相关环境影响方面的重要作用。
