High-valent iron–oxo species in heterogeneous catalysis: Formation, mechanism, and reactivity for the degradation of various emerging organic contaminants

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2024-12, Vol.501, p.157490, Article 157490
• Main Authors: Li, Yin, Hu, Jiahui, Bao, Yutian, Xiao, Yanan, Lin, Lin, Li, Bing, Li, Xiao-yan
• Format: Article
• Language: English
• Subjects: Degradation mechanism; Emerging contaminants; Fe-single atom catalyst; High-valent iron–oxo species; Quantitative structure–activity relationship (QSAR)
• ISSN: 1385-8947
• DOI: 10.1016/j.cej.2024.157490

[Display omitted] •A single-atom Fe catalyst (FeN4-C) exhibited excellent performance in PMS activation;•FeN4-C specifically generate FeⅤ=O via PMS activation for the removal of EOCs;•QSAR model relates electron donating ability (EHOMO) to EOC degradation rates.•FeⅤ=O predominantly targets electron-rich groups in EOCs;•Providing a solid theoretical framework for water purification by FeⅤ=O. High-valent iron–oxo species (FeⅣ/Ⅴ=O), generated via peroxide activation with Fe-based catalysts, have shown potential in the selective and efficient degradation of organic contaminants. However, a comprehensive understanding of the oxidative degradation mechanism induced by FeⅣ/Ⅴ=O is still pending. In this research, to unravel this oxidation mechanism, an Fe-single atom catalyst (FeN4-C) was synthesized, and FeⅤ=O was formed as the predominant reactive species upon peroxymonosulfate (PMS) activation. The FeN4-C/PMS system was experimentally studied on its catalytic oxidation behavior for the degradation of 34 typical emerging organic contaminants (EOCs) in water, exhibiting a significant variation in the pseudo first-order kinetic rate constants (kobs) among the EOCs. A quantitative structure–activity relationship (QSAR) model was established based on the molecular structure feature and measured kobs of the EOCs. The model infers that EOCs with higher electron donating ability (EHOMO) are more susceptible towards FeN4-C/PMS oxidation, implying an electrophilic reaction following the single electron transfer (SET) mechanism. Further exploration of the degradation pathways for seven representative EOCs revealed that the oxidation occurs through the abstraction of either a hydrogen atom or a nonbonded (or π) electron by FeⅤ=O, enabling processes such as C-, N-, and S-oxidation, along with N- and O-dealkylation and deamination, to effectively degrade EOCs. These research findings provide a robust theoretical framework for understanding the reaction mechanisms and predicting the degradability and removal of various EOCs by FeⅣ/Ⅴ=O for water purification.