共沉淀引发的溶解性有机质在水铁矿/水界面的分子分馏特性
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国家自然科学基金创新研究群体项目(51721093)、中国博士后基金项目(2019M660195)和广东省重点实验室专项项目(2019B121203011)资助


Co-precipitation Triggered Molecular Fractionation of Dissolved Organic Matter at the Ferrihydrite/Water Interface
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    摘要:

    土壤矿物与溶解性有机质(DOM)的相互作用会引起DOM在矿物/水界面的结构分馏,进而影响DOM在土壤中的长期保存及其环境行为。水铁矿在环境中广泛存在,可通过两种不同方式(表面吸附或共沉淀)与DOM结合。目前,鲜有研究从分子尺度上揭示共沉淀反应诱发的DOM在水铁矿/水界面的结构分馏特性。为此,通过共沉淀方式在碳/铁比(C/Fe)不同的溶液中制备水铁矿-DOM复合体,将传统光谱手段(如,紫外(UV)-可见光光谱、Fe K边X射线吸收光谱(XAS)等)和近年来兴起的电喷雾-傅立叶变换-离子回旋共振质谱(ESI-FT-ICR-MS)相结合,从分子水平解析共沉淀过程中DOM在水铁矿/水界面的结构分馏行为。结果显示:水铁矿-DOM复合体中Fe主要以水铁矿的形式存在,所占比例与C/Fe值有关,介于68.0%~95.9%之间。UV和ESI-FT-ICR-MS分析共同表明,在共沉淀过程中,水铁矿优先固定DOM中具有高分子量的富含氧的芳香性组分(主要为燃烧过程中产生的致密多环芳香类物质和维管植物来源的多酚类物质),表明无论表面吸附还是共沉淀,水铁矿均倾向于固定芳香性强的高分子量组分。此外,本研究率先发现水铁矿对DOM的结构选择性随反应时间呈一定动态变化,表现为:燃烧过程中产生的致密多环芳香类组分优先被固定在复合体中,随着反应推进,维管植物来源的多酚类组分被固定。本研究结果有助于深入理解水铁矿形成过程中,通过共沉淀作用影响DOM环境地球化学行为的分子分馏机制。<

    Abstract:

    【Objective】As the most dynamic and bioavailable fraction of the soil carbon pool, dissolved organic matter (DOM) plays important roles in a wide range of biogeochemical processes in the environment. The interaction of soil minerals with DOM would induce structural fractionation of the DOM at the mineral/water interface, thereby influencing long-term preservation and biogeochemical processes of the DOM in the soil. Ferrihydrite, a poorly crystalline iron oxide, is known to be highly reactive to DOM in the soil owing to its high specific surface area and abundant reactive binding sites. it is widespread in the environment and can associate with DOM through either adsorption or co-precipitation. However, so far, few studies have been reported on structural fractionation of DOM at the ferrihydrite/water interface induced by co-precipitation at the molecular level. 【Method】To explore molecular fractionation of DOM at the ferrihydrite/water interface during its co-precipitation process, this study prepared ferrihydrite-DOM complex separately in solutions different in C/Fe ratio via co-precipitation and adopted the technology of combining ultraviolet (UV) spectrum with electrospray ionization Fourier transform ion cyclotron resonant mass spectrometry (ESI-FT-ICR-MS) to probe changes in DOM composition after co-precipitation ended. Species of carbon and Fe in the complex were determined with the aid of X-ray photoelectron spectroscopy (XPS) and Fe K edge XAS.【Result】Results show that Fe in the complex existed mainly in the form of ferrihydrite, of which the proportion gradually decreased from 95.9% to 68.0% with the increase in initial carbon/iron (C/Fe) ratio of the solution. UV and ESI-FT-ICR-MS analysis collectively revealed that during the co-precipitation process, ferrihydrite fixed in priority aromatic components high in molecular weight and rich in oxygen (mainly combustion-derived condensed polycyclic aromatic- and vascular plant-derived polyphenols-like substances) in the DOM, leaving aliphatic components in the solution. The lower the solution in C/Fe ratio, the higher the molecular fractionation in degree. This feature is basically consistent with what has been reported about the fractionation induced by adsorption, which indicates that no matter whether in the process of adsorption or co-precipitation, ferrihydrite tends to fix DOM components high in molecular weight and aromaticity, thus leading to changes in chemical composition of the DOM as well as surface properties of the ferrihydrite, which will in turn affect sorption, transportation and transformation processes of the contaminants therein. In addition, this study was the first to find that ferrihydrite varied dynamically with the reaction in time in selectivity to structure of the DOM, that is, combustion-derived condensed polycyclic aromatics were preferentially fixed in the ferrihydrite-DOM complex, and with the reaction going on, vascular plant-derived polyphenols-like substances followed.【Conclusion】The findings in this study are expected to be able to help understand in depth the mechanism of molecular fractionation that affects geochemical behavior of DOM in the environment via co-precipitation during the process of ferrihydrite formation.

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韩兰芳,杨妍,孙可.共沉淀引发的溶解性有机质在水铁矿/水界面的分子分馏特性[J].土壤学报,2022,59(3):767-775. DOI:10.11766/trxb202009030393 HAN Lanfang, YANG Yan, SUN Ke. Co-precipitation Triggered Molecular Fractionation of Dissolved Organic Matter at the Ferrihydrite/Water Interface[J]. Acta Pedologica Sinica,2022,59(3):767-775.

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  • 收稿日期:2020-09-03
  • 最后修改日期:2020-12-01
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  • 在线发布日期: 2022-04-16
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