基于杂原子共掺杂金刚石纳米锥电氧化降解全氟化合物的性能及机理研究

Perfluoroalkyl substances (PFASs), a class of persistent organic pollutants globally distributed in environment, are refractory, highly bioaccumulative and toxic. They have been becoming environmental and human health concerns. Therefore, PFASs removal is highly desirable. Electrochemical method is effective for PFASs degradation, which has outstanding properties such as environmental compatibility, easy handling, conducting under mild conditions and avoiding the use of costly agents. However, the current electrocatalysts for PFASs oxidation suffer from high energy consumption and low efficiency. Aiming at overcoming these limitations, heteroatoms codoped diamond nanocone is proposed for electrocatalytic oxidation of PFASs, where both heteroatoms codoping and curvature effect of nanocone might enhance electrocatalytic oxidation activity, facilitate the production of strong oxidizing radicals at low potential and PFASs adsorption on electrode surface. This project will explore the method for controllable synthesis of heteroatoms codoped diamond nanocone electrode and tune its electrocatalytic oxidation activity, radical production performance and interfacial properties by changing doped heteroatoms, dopant contents, morphology and microstructure of electrode. Meanwhile, we will investigate its PFASs degradation performance, elucidate the structure-activity relationship by identifying the critical factors influencing its degradation performance, and uncover the mechanism of interfacial reaction and PFASs degradation. This work is valuable for designing novel electrodes for cost-effective degradation of persistent organic pollutants.

全氟化合物(PFASs)是一类在全球环境中普遍检出的持久性有机污染物，具有难降解性、强生物累积性和高毒性，严重威胁生态和人类健康。因此，急需PFASs处理技术。电化学法能有效降解PFASs，具有清洁、简单、温和、无需添加试剂等优点。但目前电化学降解PFASs的主要瓶颈是能耗高、效率低。本项目拟设计杂原子共掺杂金刚石纳米锥来实现低能耗下快速、高效电氧化降解PFASs，利用共掺杂和纳米锥曲率效应来增强电氧化活性、强化低电压下强氧化性自由基的产生以及促进PFASs向电极迁移。主要研究内容包括：建立杂原子共掺杂金刚石纳米锥电极的可控制备方法，研究掺杂、形貌结构对电氧化活性、产自由基性能以及界面性质的调控作用，考察电极电氧化降解PFASs的性能及关键影响因素，建立活性构效关系，分析界面反应机制和PFASs降解机理。该研究可为设计新型电极实现低成本-高效益地降解持久性有机污染物提供新思路。

全氟化合物具有难降解性和高毒性，对生态和人类健康危害大，其有效去除是水处理领域研究的难点。本项目基于电化学技术是温和、简单、清洁的全氟化合物降解技术但电极活性低、能效差的难题，采用热丝化学气相沉积和碳纳米管转晶的方法制备了不同组分、不同微观结构的高活性掺杂金刚石新型电极，通过B/N共掺杂、引入sp2C、多孔结构等调控金刚石电极的电催化性能，发现B/N共掺杂显著增强了电极的电氧化活性，sp2C有利于增强电还原活性；和传统的金刚石平面薄膜相比，多孔结构的金刚石电化学活性面积提高了3个数量级。提出了金刚石掺杂对其产自由基性能的调控作用，基于B/N掺杂金刚石电氧化硫酸盐水溶液产生SO4•−和•OH协同氧化全氟辛酸(PFOA)，在电流4.0 mA•cm-2时PFOA的降解速率达到2.40 h-1，是单独羟基氧化的2.4-3.9倍，和其它电极相比提高了PFOA的降解速率、降低了能耗，其较好的电催化性能主要来源于B/N共掺杂的协同作用增强了电氧化活性和电荷迁移速率。自由基淬灭实验结果表明PFOA降解主要通过SO4•−和•OH共同氧化，且SO4•−对降解的贡献作用大于•OH。 PFOA (C7F15COO−)的降解机理是：PFOA与SO4•‒直接反应或在阳极失电子后C7F15•被•OH氧化，转化为C6F13COO−；C6F13COO−再发生上述反应脱去CF2转化更短链的全氟羧酸直至被矿化为CO2。本研究为研发高效的电极和电化学体系用于环境污染控制提供了理论指导，在水处理领域具有应用价值。