菌生过渡金属辅酶仿生系统催化还原降解全氟有机酸机理研究

Perfluorinated acids (PFAs) are the new emerging persistent organic pollutants subsequent to polychlorinated biphenyls and dioxins, and would pose a threat to human health once the drinking water sources, such as groundwater, were polluted by them. However, the available PFAs removal technologies up to now are generally characterized by harsh reaction conditions, high treatment costs, and difficult to apply on the in situ remediation of groundwater, etc. In this study, biomimetic systems, which use bacterial transition-metal coenzymes provided by soil microorganisms as catalyst, were firstly constructed and then optimized in order to achieve the reductive degradation and defluorination of linear and branched chain PFAs, and they possess the possibility to apply on in situ remediation of groundwater. Secondly, the key influence factors and the influence mechanisms were studied during reductive degradation of PFAs in the newly constructed and optimized biomimetic systems. Thirdly, the studies on attack points, defluorination mechanisms, and degradation pathways were carried out based on electron-transfer micro-mechanisms, stable and instantaneous degradation products, and radicals. Finally, the regulation mechanisms of reductive degradation of PFAs catalyzed by transition-metal coenzymes were analyzed in order to decrease the generation of toxic and harmful degradation products and to ensure the long-term effectiveness of the biomimetic systems. The achievements of this study would not only provide theoretical basis and technical support for the prevention and control of PFAs pollution in groundwater, but also contribute to develop biomimetic degradation technology for in situ remediation of groundwater pollution.

全氟有机酸（PFAs）是继二噁英和多氯联苯之后日益引起人们重视的新型持久性有机污染物，其对地下水等饮用水源的污染具有一定的潜在健康风险，但现有PFAs去除技术普遍存在反应条件苛刻、处理成本高，且难以应用于地下水原位修复等缺点。本课题拟采用土壤微生物能够合成提供的菌生过渡金属辅酶为催化剂，构建并优化具有地下水原位修复应用前景的仿生体系，以实现温和条件下直链和支链PFAs的还原降解和脱氟，同时探讨PFAs仿生降解的关键性影响因素及其影响机制，并从电子转移的微观机制、稳瞬态降解产物和自由基等角度研究仿生降解PFAs的进攻位点、脱氟机理和降解途径。分析菌生过渡金属辅酶仿生系统还原降解PFAs的调控机制，以降低有毒有害降解产物的生成量，并确保该仿生系统的长期有效性。项目成果不仅可为防治地下水PFAs污染提供理论依据和技术支持，而且还有助于研发以仿生催化还原为核心的地下水原位修复技术。

全氟有机酸（PFAs）对我国地下水等饮用水源的污染日趋严重，存在一定的生态和健康风险，但现有PFAs去除技术普遍存在反应条件苛刻、处理成本高等缺点。本项目通过优选菌生过渡金属辅酶和电子供体，构建了维生素B12+纳米零价金属仿生降解体系，在相对温和的条件下同时实现了PFAs支链和支链异构体的还原降解和脱氟。同时，探讨了环境因素（反应温度、初始pH值等）、地下水共存物质（胡敏酸、富里酸、DO、硝酸盐等）和自身分子结构（全氟碳链长度、直支链异构体、末端官能团等）对PFAs仿生降解和脱氟的影响。.研究结果表明，VB12（钴咕啉）较血红素（铁卟啉）具有更高的催化活性，此外轴向配体也可影响VB12的催化活性；纳米零价铁及其组成的双金属体系（如纳米零价铁/镍双金属）一般更适用于仿生降解体系。PFAs的去除率和脱氟率一般随着反应温度（25℃~75℃）、初始pH值（4~10）和还原剂初始投加量（0.5g/L ~ 3.0g/L）的升高而升高；随着溶解氧和硝酸盐等竞争性电子受体浓度的增加而降低。胡敏酸和富里酸仅在高浓度时（≥100 mg/L）对PFAs的去除及其脱氟产生不利影响。PFAs的全氟碳链越长、含有支链均会导致其更易仿生去除和脱氟，此外全氟碳链长度相同的全氟烷基磺酸相较于全氟羧酸也更易去除和脱氟。.利用高斯软件基于密度泛函理论（DFT），采用B3LYP/6-31++G(d,p)及B3LYP/6-311++G(d,p)方法，计算全氟十四烷酸（PFTeDA）的12种异构体的吉布斯自由能及部分C-C键和C-F键离解能，并结合同位素标记PFTeDA（M2PFTeDA）的降解产物，研究PFAs仿生降解及脱氟降解机理：1）M2PFTeDA脱羧生成全氟自由基CF3(CF2)1113CF2•，再结合1个CF2基团生成CF3(CF2)1113CF2CF2•，接着它会在7号与8号碳间断裂，生成CF3(CF2)6•和CF3(CF2)413CF2CF2•，最后上述两自由基进一步水解生成13C1-全氟庚酸（PFHpA）和PFHpA。2） M2PFTeDA经前述反应生成CF3(CF2)6•自由基后，在2号与3号碳间断裂生成CF3(CF2)4•，其中一部分会水解生成全氟戊酸（PFPeA）；另一部分与CF2基团结合生成CF3(CF2)5•，再进一步水解生成全氟己酸（PFHxA）。