碳基吸附材料中的自由基对有机污染物环境行为的影响

Carbonaceous adsorbents are widely used in the areas of material science and technology, environmental science and engineering, energy and electrochemistry. These materials have played an important role in human daily lives and the development of the economics. It was previously reported that a great deal of free radicals were detected in these materials (carbonaceous adsorbent free radicals, CAFRs). These free radicals are very stable, showing 5% decrease in one month according the applicant’s preliminary data. We also have shown that CAFRs can react with organic contaminants and contribute up to 50% of the apparent sorption. Ignoring the degradation of organic contaminants by CAFRs will result in the wrong assignment of carbonaceous adsorbent functions. CAFR-organic contaminant interactions could also be an important process in the environment. However, their interactions were not fully investigated, and the mechanisms are unknown. This study hypothesized that the widely presented CAFRs interact actively with organic contaminants, which is an important process in organic contaminant environmental fate. Firstly, different types of carbonaceous adsorbents will be collected or prepared. CAFR quantity and property will be analyzed and compared in these carbonaceous adsorbents, to investigate the impact of matrix property and producing condition on CAFR generation and property. The activity of CAFRs will be determined through the strength of electron paramagnetic resonance (EPR) signals, generation of reactive oxygen species in aqueous phase, as well as the degradation of organic contaminants. The interaction mechanisms between organic contaminants and CAFRs will be the research focus of this study. Organic contaminants may be degraded through two different ways: 1) CAFRs may promote the generation of •OH in aqueous phase. The consequent reactions between •OH and organic contaminants resulted in their degradation. 2) Organic contaminants may be adsorbed on carbonaceous adsorbents. Their direct contact with CAFRs may result in organic contaminant degradation. Specific experiments will be conducted to identify organic contaminant degradation pathways in CAFR-containing systems. Further investigation will be carried out to clarify the impact of environmental conditions on CAFR-organic contaminant interactions. It is easily predicted that oxygen concentration, pH condition, co-existed organic molecules as well as transition metals will alter CAFR reactivity. The impact of co-existed natural organic matter (NOM) or transition metals will be studied in detail. Both NOM and transition metals will change the electron transfer in CAFR-organic contaminant systems, which will significantly change organic contaminant environmental behavior. This study will be a new input in the study of organic contaminant environmental fate, and will provide fundamental theoretical basis for the assessment and management of carbonaceous adsorbents.

碳基吸附材料在材料、环境、能源、电化学等领域广泛应用，对人类生活和经济发展有重要的作用。这些碳基材料中普遍存在大量、稳定的自由基（CAFRs），能够与有机污染物发生反应，但是这个过程一直没有得到应有的重视，忽略该过程势必引起对碳基吸附材料功能辨别上的偏差，也导致对有机污染物环境行为描述的不充分。本研究拟探讨碳基吸附材料的种类、制备工艺等对CAFRs的特征和活性的影响，理解CAFRs产生的基质条件和机制过程；深入研究CAFRs与有机污染物相互作用的机理，判别有机污染物与液相中的•OH和固相上的大分子自由基相互作用对表观降解的贡献；系统研究环境条件，重点是天然有机质和过渡金属元素对CAFRs活性的影响，初步说明CAFRs引起的有机污染物降解对其环境行为的控制性作用。本研究是对这些材料影响下有机污染物环境地球化学行为进行准确认识的必经之路，也将为碳基材料风险评估和管理提供必要的理论基础。

碳基吸附材料中的稳定自由基（CAFRs）可能具有反应活性，但是在碳基材料与污染物相互作用研究中，并没有得到充分的理解。本研究从CAFRs产生过程、结构基础为起点，识别有机污染物在碳基材料上的吸附和降解过程，重点是CAFRs在其中的作用，为污染控制基本理论和高效处理材料的开发提供基础。.本研究发现，木质素在较低温度是开始热解，成为CAFRs生成的重要结构基础；CAFRs形成的主要过程并不是热解过程中的化学键断裂，而是碳结构的重组。同时，不同生物高分子之间的交联、有机组分与无机矿物之间的相互作用对CAFRs的形成都有明显的贡献。CAFRs的自由基信号可以持续数月甚至更长时间，虽然有初期的自由基信号衰减，但以氧为中心的自由基有所增加。可能是分子氧在炭表面物理吸附，吸附态分子氧与活性位点结合发生反应，使其价键达到饱和或者形成新的自由基结构。.液相中小分子自由基的猝灭并不能完全抑制有机污染物的降解，经计算，液相中ROS对降解的贡献仅为~20%，而通过与炭上活性位点直接反应对降解的贡献可达~80%。有氧条件下，有机污染物降解速率与其取代基的电子效应参数或电极电势成线性正相关关系，表明该体系中氧化反应为主要反应途径。而在无氧条件下，这个相关性较差，表明该体系中氧化反应和还原反应同时存在。因此，生物炭上的活性位点具有不同的氧化还原电位。.在以上机制研究的基础上，探讨了紫外光照、水洗处理生物炭颗粒、弱酸洗矿以及生物炭DOM回加等条件影响下，生物炭性质与有机污染物光降解的关系，指出，可溶性组分可能覆盖生物炭颗粒表面并堵塞活性位点；矿物成分在RhB光降解过程中的作用是有限的；总体而言，生物炭体系对有机化学物质的降解可能与生物炭颗粒中的CAFRs和溶出的DOM的相互作用有关。.以上研究表明，对生物炭异质性结构的深入理解和调控，可能是实现高效污染物控制的有效途径。如何调控生物炭的结构，实现其氧化或者还原功能的高效利用，是本研究团队下一步的工作重点。