生物炭-铁体系中有机污染物的降解：电子得失和电子传导作用的区分

Recently, biochars have attracted a great amount of research attentions due to their projected wide applications. Because of their quinone/hydroquinone surface groups and graphite subsurface structures, biochars not only can reversibly accept and donate electrons to involve in redox reactions, but also act as efficient electron shuttles to conduct electrons. Both processes are involved in organic contaminant degradation in biochar-iron system. However, current researches have not successfully distinguished these two different electrons transfer processes, which would lead to the incomplete understand of the degradation mechanisms of organic contaminants in biochar-iron system. Consequently, our understanding on the biochar industrial application developments and environmental impacts could be limited. Because of the ubiquitous of iron existing in the environment, biochar-iron interactions will greatly alter the electron transfer in the system. In this proposed project, we plan to explore the mechanisms of biochar-iron complex in mediating organic pollutant degradation. The main focus of this research is to distinguish the electron transfer pathways through different physic structures including electrons exchange moieties and graphite. In order to systematically connecting biochar structures to these two basic electron transfer processes, this research will compare the characteristics of electron shuttling among biochars produced at different pyrolysis temperatures and feedstocks. Based on the characterization of fundamental biochar structures, combined with the experiments of organic contaminant degradation kinetics and by-products identification, the degradation mechanisms of organic pollutants in biochar-iron system can be addressed. This project will also explore how humic substance will overcome the electron transport restricted by spatial heterogeneity of biochars and the distance between iron and organic chemicals. This project results will provide fundamental insights into biochar efficient implements and functional developments in soils. And the conclusions of this work will also contribute to the vital basics for the precise prediction of biochar geochemistry processes.

近年来，生物炭作为电子传递介质受到研究人员的广泛重视。由于其表面醌/氢醌基结构以及内部石墨化碳结构，生物炭既能以电子得失的形式参与氧化还原，又能作为高效的电子穿梭体介导电子传导。当前的研究不能明确区分这两个过程，导致对生物炭-铁体系中有机污染物降解机制的理解不完整，制约了生物炭应用技术的开发和环境效应的准确认识。本项目拟研究生物炭-铁体系中有机污染物的降解机制，重点区分电子得失与电子传导这两者的作用。通过比较不同母源物质，不同热解温度下生物炭的电子传递特征，对电子得失和电子传导的生物炭结构基础形成系统的理解。在此基础上，结合生物炭-铁体系中有机污染物降解动力学和降解产物鉴定，本研究拟对有机污染物降解机制有更加清晰的阐释；并初步探索腐殖质介导下，该体系如何突破空间距离和非均质属性对电子传递的制约。本研究是生物炭有效应用和功能开发的理论依据，也是准确预测生物炭环境地球过程的重要基础。

生物炭是一种环境友好的富碳材料具有广阔的应用前景。由于其表面醌/氢醌基结构以及内部石墨化碳结构，生物炭既能以电子得失的形式参与氧化还原，又能作为高效的电子穿梭体介导电子传导。然而，目前的研究就这两个过程对生物炭降解有机物污染物的贡献不明确，导致当生物炭应用于土壤后，土壤中活性金属氧化物（例如铁）对生物炭吸附和降解有机污染物的的机制理解不完整。本项目通过比较不同热解温度下生物炭与Fe3+离子的相互作用特征，结合生物炭-铁体系中有机污染物对硝基苯酚的吸附降解实验，及包括电子顺次共振、X射线光电子能谱在内的众多表征手段，揭示了生物炭与Fe3+离子相互作用的过程中，生物炭上的C-O能够还原Fe3+离子而C=O能够把Fe固定在生物炭表面形成Fe(II)与Fe(III)共存的铁氧化物，研究结果显示，生物炭上对有机污染物的降解取决于生物炭上含氧官能团得失电子的能力，只有当生物炭上的含氧官能团的氧化还原电位高于O2时，生物炭才能有效降解有机污染物。在生物炭-铁系统中，Fe3+会抑制生物炭对有机污染的降解，但O2浓度的增加能提高污染物的降解效果，还能消除Fe3+离子对有机物降解的抑制作用，因此改变环境因子的得失电子能力可作为生物炭降解有机污染物的有效调控手段。本研究还发现环境中的Fe3+离子并不会影响生物炭持久性自由基的活性和强度，生物炭上的持久性自由基的强度与其对污染物的降解活性没有直接关系，持久性自由基的种类决定了其反应活性。生物炭持久性自由基及石墨化结构能有效稳定有机污染物降解过程中的中间产物，导致持久性自由基信号强度的上升，因此仅通过测定持久性自由基的强度，并不足以预测其在环境中的环境效应与环境风险。本研究的结论为理解和预测生物炭在土壤环境迁移过程中对污染物的降解过程产生的影响提供了理论依据，同时也为生物炭在土壤中降解有机污染物提供调控方法与理论支撑。