【作者】 王海龙；

【导师】 张慧敏； 张萌；

【作者基本信息】 华东交通大学 ， 资源与环境（专业学位）， 2023， 硕士

【摘要】 作为全球氮循环平衡中的重要一环,氨氮也是水体中氮污染物的主要形态之一,一旦过量排放,易引发水体富营养化、水体黑臭等棘手的环境问题。针对氨氮废水的高效处理,经济环保的直接电化学氧化技术被寄希望于研究和应用。近年来,由于双金属之间具备良好电子协调效应,价廉易得的NiCu电极在氨氧化反应(AOR)领域拥有巨大的催化潜力。然而,一直面临着催化电极过电位大、活性位点暴露不足等缺点导致的阳极AOR动力学迟滞,以及产物选择性低下的问题。为此,本工作基于掺杂改性、异质结构建、缺陷工程和原子级工程等表/界面调控策略,对NiCu电极进一步优化设计,改善内部电子结构,深度调控活性位点的形成与暴露,促使AOR在更低电位下迅速启动。考察各催化电极的形貌结构与物相组成、电化学性能以及电氧化脱氮处理效用,为稳定高效的催化电极的合理设计和开发提供行之有效的方法与理念,并推动直接电化学氧化技术在氨氮废水处理领域的应用。主要研究内容如下:(1)通过水热合成法和碱性电化学调谐策略合成了一种稳定高效的Ni1Cu3-S-T/CP催化电极。硫离子的动态迁移对表面重构层次的深度调控促使活性物种充分形成与暴露,有效地降低反应能垒。借助理论模型和计算,提出并验证了NiCu催化电极在催化AOR过程中Cu的作用机制,可以调控电极材料的d带中心和态密度,以优化其内源电子结构。实验结果显示,Ni1Cu3-S-T/CP催化电极以150 mA/cm2的高电流密度表现出卓越的AOR活性;运行5小时后NH4+-N去除效率达到96.23%,且表现出强循环稳定性。不仅为优良的NiCu催化电极的可控合成提供了一个范例,也利于推动直接电化学氧化技术的发展,实现废水中氨氮的高效去除。(2)借助电化学沉积和碱性电化学调谐策略,Co、S共掺杂成功构建了一种三维纳米花状结构Ni1Cu1Co0.5-S-T/CP催化电极。特殊的三维异质结结构提供了大量的离子传输通道,为AOR动力学的加快奠定了一个良好的基础条件;Co进一步增强了金属间的电子相互协调效应,降低了 AOR的起始电位。实验结果表明,Ni1Cu1Co0.5-S-T/CP催化电极具有优良的AOR活性,并实现了废水中氨氮的高效降解,NH4+-N去除效率高达98.07%,伴随着81.21%的高氮气选择性。这对于异质结类催化电极的构建有一定指导意义,便于推进氨氮废水的绿色高效处理。(3)通过简单的固相热解方法合成了锚定在氮掺杂碳中的NiCu3-N-C DAC,创新地设计了一种NiCu双原子位点催化剂。借助HAADF-STEM和XAFS分析手段,证实了相邻双原子位点的存在,并揭示了 Ni-N4/Cu-N4基团的局部配位环境。结果表明,NiCu3-N-C DAC所构建的电催化体系中,运行6小时后NH4+-N去除效率达到99.52%,N2选择性达到99.58%,FE为86.60%,且可以维持至少36小时内稳定性。同时,简述了该催化剂与纳米级催化剂之间氨氮降解机制的差异。总之,拥有特定的双原子位点结构的NiCu3-N-C DAC可以实现氨氮高效降解的同时,也可以实现产物资源化和无害化。这不仅对多元协同单原子催化剂的合理设计有一定指导意义,也推动了氨氮废水的绿色高效处理,助力“双碳”政策的贯彻与落实。更多还原

【Abstract】 As an important part of the global nitrogen cycle balance,ammonia-nitrogen is also one of the main forms of nitrogen pollutants in water bodies.Once discharged in excess,it can easily cause serious environmental problems such as eutrophication and black odor of water bodies.For the efficient treatment of ammonia-nitrogen wastewater,the economical and environmentally friendly direct electrochemical oxidation technology is expected to be researched and applied.Recently,cheap and readily available NiCu electrodes have shown great catalytic potential in the field of ammoxidation(AOR)due to the good electronic coordination effect between bimetals.However,it has been faced with many problems,such as anode AOR kinetic hysteresis resulting from the shortcomings of high overpotential,insufficient exposure of active sites,and low selectivity of products.In this work,the design of NiCu electrodes is further optimized by surface/interface regulation strategies,such as doping modification,heterostructure construction,defect engineering and atomic level engineering.It is to improve the internal electronic structure and deeply regulate the formation and exposure of active sites,thereby promoting the rapid initiation of AOR at lower potentials.The morphological structure and phase composition,electrochemical performance and electro-oxidative nitrogen removal treatment utility of each catalytic electrode are examined.Providing proven methods and concepts for the rational design and development of stable and efficient catalytic electrodes,as well as advancing the application of direct electrochemical oxidation technology in the field of ammonia-nitrogen wastewater treatment.The main research contents are as follows:(1)A stable and efficient Ni1Cu3-S-T/CP catalytic electrode was synthesized through hydrothermal synthesis and alkaline electrochemical tuning strategy for AOR.The dynamic migration of sulfur ions deepens surface reconfiguration level to promote the full formation and exposure of active species,which effectively reduces the reaction energy barrier.With the help of theoretical models and calculations,the function mechanism of Cu of NiCu-based catalytic electrodes in the catalytic AOR process is proposed and verified,which can regulate the d band center and state density of electrode materials to optimize its endogenous electronic structure.The experimental results showed that the Ni1Cu3-S-T/CP catalytic electrode exhibits excellent AOR activity with a high current density of 150 mA/cm2;After 5 hours of operation,the removal efficiency of NH4+-N reached 96.23%,and it showed strong cycling stability.It not only provides an example for the controllable synthesis of excellent NiCu-based catalytic electrodes,but also facilitates the efficient removal of ammonia-nitrogen in wastewater.(2)With the help of electrochemical deposition and alkaline electrochemical tuning strategy,Co and S co-doping successfully constructed a three-dimensional(3D)nanoflower-like structure Ni1Cu1Co0.5-S-T/CP catalytic electrode.The special 3D heterojunction structure furnishes a large number of ion transport channels,which lays a good foundation for the acceleration of AOR kinetics.Co further enhances the inter-metal electron coordination effect,reducing the onset potential of AOR.The experimental results displayed that the Ni1Cu1Co0.5-S-T/CP catalytic electrode has excellent AOR activity,then realized the efficient degradation of NH4+-N in wastewater,namely the removal efficiency up to 98.07%accompanied by 81.21%high N2 selectivity.This has certain guiding significance for the construction of heterojunction catalytic electrodes,which is convenient for giving impetus to the green and efficient treatment of ammonia-nitrogen wastewater.(3)NiCu3-N-C DAC anchored in nitrogen-doped carbon was synthesized by simple solid-phase pyrolysis method,where an NiCu diatomic site structure was innovatively designed.By means of HAADF-STEM and XAFS analysis methods,the existence of adjacent diatomic sites was confirmed and local coordination environment of Ni-N4/Cu-N4 groups was revealed.The results show that after 6 hours of operation in the electrocatalytic system constructed by NiCu3-N-C DAC,NH4+-N removal efficiency reached 99.52%,N2 selectivity reached 99.58%,FE was 86.60%,and stability could be maintained for at least 36 h.Meanwhile,the variations in the degradation mechanism of NH4+-N between the catalyst and the nanoscale catalyst are briefly described.In conclusion,NiCu3-N-C DACs with specific diatomic site structures can achieve efficient degradation of NH4+-N,realizing resource utilization and harmlessness of product.This not only has certain guiding significance for the rational design of multi-synergistic single-atom catalysts,but also promotes the green and efficient treatment of ammonia-nitrogen wastewater,helping the implementation of the“dual carbon”policy.更多还原