基于碳复合气体扩散电极的电催化高级氧化技术降解典型抗生素生产废水的机理研究

The antibiotic yearly output from our country is on the top of the world. The antibiotic production wastewater contains refractory organic pollutions, high salinity and strong biotoxicity. The traditional wastewater treatment technology is hard to meet the national standard. Electro-Fenton technology, as representative of the electro-catalytic advanced oxide process, has advantages of quick reaction, security and environmental protection and simple devices. In particular, it can use the salt of the antibiotic wastewater as the electrolyte, realizing the resource utilization. Therefore, it has great applicable potential in the field of the high-salinity organic wastewater treatment. However, it is now awfully constrained by narrow pH range, barely catalyst reuse, and secondary pollution, which are mainly caused by using Fe and analogous metal catalyst. In order to solve that, it is urgently necessary to explore an alternative nonmetallic catalyst. This project will prepare a carbon-composite gas diffusion electrode where a catalytic layer of carbon black and carbon nanotube will be modified by reduced graphene oxide via electrochemical method. The fabrication method will be firstly optimized by testing the production efficiency of oxygen-containing radical and characterizing the electrode structure. Furthermore, the crucial electrode characterizations should be selected. The migration and transformation behaviors of the oxygen in the gas diffusion electrode will be analyzed depending on a comprehensive probe-monitoring device. Based on that, the inherent relationship between the oxygen behaviors and electrode characterizations can be explored and further the producing mechanism of oxygen-containing radical on the carbon-composite gas diffusion electrode can be clarified. By using typical antibiotic production wastewater as the target pollutant, the in-situ electro-catalytic degradation capacity of the carbon-composite gas diffusion electrode will be studied. The adsorption and degradation process of the antibiotics in the system will be investigated, respectively. The influences of the electrolysis parameters and water quality conditions will be discussed. Then, the mass transfer and transformation behavior of the antibiotics on the interface of electrolysis-electrode will be specially analyzed. Its effect on the oxygen reduction reaction will also be assessed. Based on that, the removal mechanism for antibiotics in this system will be clarified. In addition, the influences of the molecular structure of the antibiotics on the performance will be given. The research findings of the project will lay great foundation for the development of the environment-friendly electro-catalytic advanced oxidation process, especially for antibiotic production wastewater.

我国抗生素行业排放的生产废水具有难降解、盐分高、生物毒性强等特点，传统水处理技术难以满足国标要求。电-Fenton技术反应快速、设备简单、安全性高，是目前最有前景的电催化高级氧化技术之一。抗生素废水中的盐分恰好可以在电-Fenton体系中充当电解质，强化了其处理优势。然而目前常用的金属催化剂会导致pH范围小、催化剂回用率低、引发二次污染等问题，寻找可替代的非金属催化剂势在必行。本项目拟制备电化学还原氧化石墨烯修饰的碳复合气体扩散电极，原位电催化还原氧气生成强氧化性自由基。通过探明电极特性与氧气迁移、转化行为之间的相关性，优化电极材料，揭示自由基的产生机理。进而将该电极用于电催化降解典型抗生素生产废水，通过等温吸附与电催化降解实验，提高降解性能，揭示降解机理，阐明抗生素分子结构特点的影响机制。本项目能够为非金属阴极电催化高级氧化技术的发展及其在制药行业废水处理中的应用奠定理论和实践基础。

我国的抗生素生产废水具有难降解、盐分高、生物毒性强、排放量大等特点，传统水处理技术无法满足国标要求。光电催化高级氧化技术具有反应快速、安全环保和设备简单等特点，特别是可以利用废水中的盐分充当电解质，提高资源利用率。本项目构建了基于碳复合空气阴极的光电催化高级氧化体系，优化了空气阴极的制备技术、阐明了光电催化还原氧气的反应机理、解析出抗生素降解路径以及降解动力学与运行参数之间的内在关联。首先筛选出石墨作为空气阴极的主体碳材料，制备的单层结构空气阴极在3.5mAcm-2下2h产过氧化氢700mgL-1。然后利用电化学方法在空气阴极表面修饰RGO，增加紫外光对于自由基产生量的贡献。成功利用有机溶剂分散GO，在正电位吸附+负电位还原的模式下获得了均匀的RGO膜，有效克服了水解析氢微气泡阻碍GO分子向空气阴极迁移吸附的问题。设计了具有多面光窗的反应器探索RGO/石墨空气阴极催化氧还原产自由基的反应机制。主要途径是氧气首先还原生成过氧化氢，继而被紫外光激发产生羟基自由基。次要途径包括RGO本身电子以及光激发产生的光电子向过氧化氢转移产生自由基，以及光激发生成的空穴氧化水分子产生氧自由基。最后分别以青霉素G钠和诺氟沙星两种典型的抗生素作为目标污染物考察降解能力。二者的TOC去除率分别可达到95.6%和80%，矿化电流密度可达到56.8%。自由基对抗生素结构没有氧化选择性，降解路径主要涉及取代、开环、氧化、脱羧反应。降解过程水体的生物毒性先升高后降低，说明初级中间产物的毒性高于原是抗生素分子。重点考察了电流密度、pH值、抗生素初始浓度、电解质浓度对TOC去除率的影响，关联性分析显示pH值和抗生素初始浓度的影响最大，而且适用于处理中性废水，对于酸碱性和抗生素浓度波动的抗冲击能力较强。该技术避免了使用金属催化剂导致的pH处理范围窄、催化剂回用率低、引发二次污染等问题，研究成果为推动高效低耗、安全环保降解高盐有机废水提供了理论指导和数据支撑。