【作者】 苏毅；

【导师】 王艳；

【作者基本信息】 华南理工大学 ， 环境科学与工程， 2024， 硕士

【摘要】 基于过硫酸盐（PS）的高级氧化技术是目前去除水体环境中日益增多的内分泌干扰物（EDCs）的有效方案。该技术的关键在于如何实现PS的高效活化,而传统的均相活化存在效率不高、易产生二次污染和需要外加能量等问题,因此目前研究者更关注非均相活化方式。铁、氮共掺杂的碳材料（Fe-N-C）具有较高反应活性的同时也具有更好的稳定性和可重复使用性,这些优点使其成为活化PS的理想催化剂之一。但目前,Fe-N-C催化剂还存在稳定性差、催化机制尚不明确、对称结构的Fe-N活性位点存在催化惰性、污染物降解效率不高等问题。针对以上问题,本研究以沸石咪唑框架为前驱体,分别制备了Fe-N/O@C和Fe-Co-N@C两种催化剂,深入分析其配位结构差异、催化机理及污染物降解路径。通过以富含含氧官能团的葡萄糖酸亚铁作为Fe源,将O原子引入了Fe-N-C材料结构中,成功合成了具有N₂-Fe-O₂配位结构的Fe-N/O@C-X催化剂。研究表明,Fe-N/O@C-800表现出优异的PMS催化性能,对BPA的降解效率在60 min内高达99.4%,与Fe-N@C-800和N@C-800相比,降解速率分别提高了2.38倍和17.6倍。降解效率的提高归因于Fe的掺杂、配位结构的引入和碳层结构的石墨化程度的改变丰富了活性位点的种类和数量,而O的掺杂打破了Fe-N₄结构的催化惰性增强了催化活性。循环实验表明Fe-N/O@C-800在四次循环内均能保持90%以上的BPA去除率,同时催化剂的结构没有受到破坏。在2-10的宽p H范围内,Fe-N/O@C-800都表现出94%以上的高BPA去除率,无机阴离子和腐殖酸的存在对Fe-N/O@C-800/PMS体系的降解效果没有明显影响,这些实验结果表明Fe-N/O@C-800具有较高的催化活性和稳定性能,对于解决Fe-N-C催化剂稳定性差、降解效率不高的问题展现出良好的应用前景。采用三步法合成了Co掺杂的Fe-Co-N@C催化剂。相比于Co-N@C和Fe-N@C而言,Fe-Co-N@C表现出最好的PMS催化性能,其反应速率分别是后两者的2.93倍和1.41倍。同时,Fe-Co-N@C具有最高的I_D/I_G,证明了缺陷程度最高。XPS光谱分析结果显示Fe-Co-N@C的Fe 2p和Co 2p的特征峰向低结合能偏移,表明其电子密度增加,同时吡啶N/M-N、C-O/C-N和C=O等活性位点作为电子供体给出电子以活化PMS,而吡咯N和石墨N则作为电子受体实现电子转移。循环实验表明Fe-Co-N@C在三次循环内都能保持较高的催化活性。密度泛函理论计算（DFT）计算和LC-MS的分析结果表明BPAF的降解路径包括ROS攻击酚羟基和两个BPAF分子之间发生H-吸收和耦合,最后进一步分解矿化。为了进一步明确催化机理,我们通过淬灭实验和电子顺磁共振波谱检测鉴定了Fe-N/O@C-800/PMS降解BPA体系中存在的活性氧物种,证实了BPA的降解是由¹O₂和≡Fe（Ⅳ）=O的非自由基途径主导。通过DFT计算研究了N₂-Fe-O₂和Fe-N₄两种配位环境对极化电场和ROS产生的影响机制:O的掺杂降低了Fe原子的氧化态,富电子的Fe中心和局部极化电场发生偏移,改变了PMS断键方式实现了自由基和非自由基共同作用的活化途径转变为仅非自由基起作用的活化路径。Fe-Co-N@C/PMS降解BPAF体系的淬灭实验和EPR检测证实了¹O₂是起主要作用的ROS,同时结合DFT计算阐明了金属原子掺杂调控极化电场及活化PMS的机制:Co的掺杂增加了活性位点的数量和种类,同时与Fe的共配位打破了Fe-N₄对称结构的催化惰性,使得Fe原子的电子密度增加,因此Fe-Co-N配位结构相比于单金属结构具有更高的极化电场强度、更强的PMS吸附能力和给电子能力,因此具有更高的催化活性。更多还原

【Abstract】 The advanced oxidation technology based on persulfate（PS）is currently an effective solution for removing the increasing number of endocrine disrupting substances（EDs）in aquatic environments.The key challenge of this technology lies in achieving efficient activation of PS.Traditional homogeneous activation suffers from low efficiency,secondary pollution,and the need for additional energy input,thus researchers are now more focused on heterogeneous activation methods.Iron and nitrogen co-doped carbon materials（Fe-N-C）exhibit high reactivity along with better stability and reusability,making them ideal catalysts for activating PS.However,current Fe-N-C catalysts still face issues such as poor stability,unclear catalytic mechanisms,catalytic inertness of symmetric Fe-N active sites,and low efficiency in pollutant degradation.Addressing these challenges,this study utilizes zeolitic imidazolate framework（ZIF）precursors to synthesize two catalysts,Fe-N/O@C and Fe-Co-N@C,and conducts in-depth analysis of their structural differences,catalytic mechanisms,and pollutant degradation pathways.By using gluconic acid iron rich in oxygen-containing functional groups as the Fe source,oxygen atoms were introduced into the Fe-N-C material,successfully synthesizing the Fe-N/O@C-X catalyst.Research has shown that Fe-N/O@C-800 exhibits outstanding catalytic performance with peroxymonosulfate（PMS）,achieving a degradation efficiency of bisphenol A（BPA）as high as 99.4%within 60 min.Compared to Fe-N@C-800 and N@C-800,the degradation rates have respectively increased by 2.38 times and 17.6 times.The enhancement in degradation efficiency is attributed to Fe doping,the introduction of coordination structures,and changes in the graphitization degree of the carbon layer,which enriches the types and quantities of active sites.Additionally,oxygen doping breaks the catalytic inertness of the Fe-N₄ structure,enhancing catalytic activity.Cycling experiments demonstrate that Fe-N/O@C-800 maintains a BPA removal rate of over 90%within four cycles without structural damage to the catalyst.Over a wide p H range of 2-10,Fe-N/O@C-800 exhibits BPA removal rates of over94%,and the presence of inorganic anions and humic acid has minimal impact on the degradation efficiency of the Fe-N/O@C-800/PMS system.These experimental results indicate that Fe-N/O@C-800 possesses high catalytic activity and stability,showing promising applications in addressing the issues of poor stability and low degradation efficiency associated with Fe-N-C catalysts.We synthesized Co-doped Fe-Co-N@C catalyst using a three-step method.Compared to Co-N@C and Fe-N@C,Fe-Co-N@C exhibited the best catalytic performance for PMS activation,with reaction rates 2.93 times and 1.41 times higher,respectively,than those of the latter two.Fe-Co-N@C had the highest I_D/I_G ratio,indicating the highest number of active sites.XPS spectroscopy showed a low-binding energy shift in Fe 2p and Co 2p peaks of Fe-Co-N@C,suggesting increased electron density.Meanwhile,pyridinic N/M-N,C-O/C-N,and C=O active sites served as electron donors for PMS activation,while pyrrolic N and graphitic N acted as electron acceptors for electron transfer.Cycling experiments demonstrated that Fe-Co-N@C maintained high catalytic activity over three cycles.Density functional theory（DFT）calculations and LC-MS analysis revealed the degradation pathway of BPAF,involving ROS attacking phenolic hydroxyl groups and subsequent H-absorption and coupling between two BPAF molecules,ultimately leading to further mineralization.To further elucidate the catalytic mechanism,we conducted quenching experiments and used electron paramagnetic resonance（EPR）spectroscopy to identify reactive oxygen species（ROS）present in the Fe-N/O@C-800/PMS system during BPA degradation,confirming that the degradation of BPA was predominantly driven by the non-radical pathways of ¹O₂ and≡Fe（Ⅳ）=O.Through DFT calculations,we investigated the effects of two coordination environments,N₂-Fe-O₂ and Fe-N₄,on polarized electric（PE）fields and ROS generation mechanisms:Oxygen doping lowered the oxidation state of Fe atoms,causing a shift in electron-rich Fe centers and local polarized electric fields,thereby altering the PMS cleavage pathway from a cooperative activation involving both radicals and non-radicals to a pathway solely dependent on non-radicals.Quenching experiments and EPR detection in the Fe-Co-N@C/PMS BPAF degradation system confirmed that ¹O₂ played a primary role as the ROS.Additionally,combining these experimental findings with DFT calculations clarified how metal atom doping regulates polarized electric fields and PMS activation mechanisms:Co doping increased the quantity and variety of active sites,while its coordination with Fe disrupted the catalytic inertness of the Fe-N₄ symmetric structure,leading to an increase in electron density at Fe atoms.Consequently,the Fe-Co-N coordination structure exhibited higher polarized electric field strength,stronger PMS adsorption capability,and electron-donating ability compared to single-metal structures,resulting in enhanced catalytic activity.更多还原