石墨相氮化碳表面官能化与活化过硫酸盐降解水中有机污染物机理

In response to the ubiquitous problem of water pollution caused by refractory organic contaminants in China and the development status of persulfate-based advanced oxidation process, the project proposes to extend the degree of π-electron delocalization on the surface of graphitic carbon nitride (g-C3N4) by means of the implementation of various surface functionalization of g-C3N4, enhancing the interaction and interfacial electron transfer between the surface-functionalized g-C3N4 and persulfate and increasing the production rate of reactive species. This project focuses on the treatment of endocrine disrupting compounds, pesticides and perfluorinated compounds from aqueous solution, and the determination of structure-activity relationship between the structural characteristics of surface functional groups on g-C3N4 and properties of persulfate activation. The investigation of solid-liquid micro-interfacial reaction process of surface functional groups onto g-C3N4, persulfate and contaminants, and the elucidation of oxidative degradation mechanism of organic pollutants in the heterogeneous persulfate process were performed to provide the basis for the development of novel, efficient, metal-free catalysts toward persulfate activation. Furthermore, the degradation kinetics of pollutants were investigated to optimize the reaction process and to establish a highly effective and stable persulfate fixed bed wastewater treatment system. Then, the established system was combined with the biological oxidation technology to explore the effectiveness of treatment of recalcitrant organic pollutants, providing scientific basis and technical support for the practical application of heterogeneous persulfate-based advanced oxidation process.

针对我国水源普遍存在难降解有机物污染的问题，和过硫酸盐高级氧化技术发展状况，本项目提出通过对石墨相氮化碳(g-C3N4)进行不同表面官能化，增加g-C3N4表面π电子离域程度，增强其与过硫酸盐相互作用，强化二者界面电子转移，提高活性物种生成速率。重点处理水中内分泌干扰物、农药和全氟化合物，确定g-C3N4表面官能团结构特征与活化过硫酸盐性能的构效关系。研究g-C3N4表面官能团、过硫酸盐与污染物固液微界面反应过程，阐明污染物在非均相过硫酸盐体系中的氧化降解机理，为新型高效非金属活化过硫酸盐催化剂的研制提供依据。进一步研究污染物降解动力学，优化反应工艺，建立高效稳定的过硫酸盐固定床废水处理系统，并与生物氧化技术联合，考察其处理难降解有机污染物的效能，为非均相过硫酸盐高级氧化技术实际应用提供科学依据和技术支撑。

针对我国水源普遍存在难降解有机物污染的问题，和过硫酸盐高级氧化技术发展趋势，本项目通过调控电子结构设计合成高活性催化剂用于活化过硫酸盐降解水中有机污染物。利用非金属元素掺杂和石墨碳环共轭对石墨相氮化碳进行表面官能化，激发表面极化形成电子高、低密度区域，增强表面官能化氮化碳与过硫酸盐固液界面电荷传递，在无外加辅助条件下实现过硫酸盐高效活化，促进活性氧物种生成，加速有机污染物氧化。与常规过硫酸盐活化过程中过一硫酸盐通常只充当电子受体不一样，结合实验结果和理论计算，我们首次提出了过一硫酸盐同步氧化还原的新活化机制，即过一硫酸盐在氮化碳表面电子高密度区得到电子发生还原生成羟基自由基和硫酸根自由基，在电子低密度区给出电子发生氧化产生过一硫酸根阴离子自由基，其随后与水分子迅速反应转化为单线态氧。高活性自由基与非自由基物种—单线态氧共同作用于有机污染物氧化降解。得益于反应过程中催化剂表面电荷动态平衡，表面官能化氮化碳在过硫酸盐活化过程中表现出良好的稳定性和可重复利用性。过一硫酸盐同时氧化还原活化机制也同步扩展到氮掺杂碳材料与金属-氮-碳材料活化过硫酸盐领域，表明该独特反应机制在过硫酸盐活化过程中的普遍性。同时借助实验分析与理论计算，揭示了（1）非金属氮掺杂碳材料活化过一硫酸盐反应中单线态氧新来源：来自于过一硫酸盐在邻近石墨氮的缺电子碳原子周围的氧化；（2）单原子铁催化剂高活性来源于单原子分散的Fe–pyridinic N4配位结构，除了富电子单原子铁作为活性位点，与4个吡啶氮原子键合的8个缺电子碳原子也充当催化位点，大大地增加了活性位点数目，显著增强过硫酸盐活化。上述结果不仅丰富过硫酸盐反应理论，而且为设计合成高活性与稳定性催化剂用于过硫酸盐介导的环境修复过程提供理论指导与技术支撑。