沉积物黑碳的电子转移能力对纳米零价铁降解PCBs的影响

Electron transfer of natural organic matter is the basis of transformation of pollutants in sediment. Recent research found that the graphene phenomenon of pyrogenic black carbon caused direct electron transfer by the carbon matrix. Moreover, the rate of this direct electron transfer was three times higher than that of charging-discharging mechanism caused by functional groups, which implied sediment black carbon might play greater role in pollutant conversion than previous assumption. To verify this theory, our project will choose the degradation of polychlorinated biphenyls (PCBs, a typical persistent organic pollutants) by nZVI as a model to study. The efficiency of PCBs dechlorination under the adsorption (inhibition) and electron transfer (promotion) of black carbon will be investigated through the following procedures: on the basis of the analysis of electron transfer function of various black carbons produced from different precursors and temperatures, 1) investigate the influence of black carbon on the degradation of PCBs in water, and then explore the reaction between different types of black carbon and nZVI by system characterization and product identification; 2) investigate the influence of black carbon on the degradation of PCBs in sediment, and analyze the activity of different forms of PCBs and then build PCBs residual prediction model through studying electron transfer behavior of aging black carbon, desorption kinetics as well as PCBs degradation kinetics of aged black carbon. It is expected this project can not only clarify the role of sediment black carbon in the chemical reduction of pollutants, but also provide new insights in developing efficient carbon-nZVI repair materials.

天然有机质电子转移是沉积物中污染物转化的重要组成部分。近年研究发现，热解黑碳的石墨烯化使碳母体可直接进行电子传递，其速率是传统官能团充放电传递速率的三倍，这暗示着黑碳的作用要比预想大得多。为证实该设想，本项目利用纳米零价铁（nZVI）降解典型持久性有机污染物多氯联苯（PCBs）这一反应，通过研究黑碳吸附（抑制）与电子转移（促进）双重作用下该反应的脱氯效果，探讨沉积物黑碳电子转移对污染物降解的影响：在分析不同类型黑碳电子传递特征的基础上，一方面研究黑碳对水相中PCBs降解的影响，通过表征与产物鉴定，探讨黑碳与nZVI的作用机理；另一方面，采用外源添加法研究沉积物中黑碳对该反应的影响，结合老化态黑碳电子转移性能、解吸动力学和降解动力学，分析不同形态PCBs降解活性，建立残留预测模型。该研究不仅可以明晰沉积物黑碳在污染物化学还原反应中的作用，也将为开发高效的碳-nZVI修复材料提供新思路。

本项目利用纳米零价铁（nZVI）还原典型持久性有机污染物多氯联苯（PCBs）这一反应，研究黑碳的吸附（抑制）与电子转移（促进）双重作用对污染物脱氯降解的影响：一方面选取了不同热解温度、不同类型的环境典型黑碳，研究了水相中单一黑碳、新鲜黑碳-沉积物体系对PCBs的吸附解吸特性及其机理。在吸附研究的基础上，以单一黑碳体系为对象，采用对PCBs脱氯活性较好的双金属改性纳米零价铁，研究其对黑碳上吸附态PCBs的降解性能。其一证实了基金申请时提出的假设：PCBs的降解受到黑碳吸附作用和电子传递作用共同影响，吸附作用抑制了PCBs的降解，而黑碳的电子传递作用可一定程度上促进吸附固定在黑碳上的PCBs的降解；其二，通过TENAX解吸动力学探讨了PCBs在黑碳上的吸附形态，分析了PCBs的吸附解吸过程与黑碳的电子传递作用对不同吸附形态PCBs化学可降解性的影响。另一方面，在水相研究的基础上，通过外源添加法探讨了黑碳-沉积物体系中黑碳对PCBs降解的影响，为nZVI对沉积物/土壤中PCBs污染修复效果的评估和后续新技术的研发奠定了基础。