Joule-thermal synthesis of graphitic carbon-encapsulated Fe/Fe ₃ N/FeN catalysts for efficient peroxymonosulfate activation toward quinoline degradation

Nanostructured iron-based catalysts have garnered significant attention due to their application in heterogeneous Fenton reactions aimed at organic pollutant degradation. However, these catalysts often exhibit limited activity and stability under oxidation conditions. In this study, a novel graphitic carbon-encapsulated Fe/Fe₃N/FeN catalyst (Fe-NC-FJH) was synthesized using a carbon-assisted flash Joule heating (FJH) method. The catalyst was specifically engineered to activate peroxymonosulfate (PMS) for effective quinoline degradation, with the fundamental mechanisms governing its catalytic activity being elucidated. Experimental results demonstrated that Fe-NC-FJH exhibited significantly enhanced degradation efficiency and a higher pseudo-first-order degradation reaction kinetic rate (<i>k</i> = 0.18 min^-1), which was 2.14 times greater than that achieved by catalysts prepared using conventional pyrolysis methods. Density functional theory calculations suggested that the graphitic carbon encapsulation enhanced the adsorption of Fe-NC-FJH for the hydroxyl O atom of PMS, thereby increasing the yield of SO₄˙^- radicals crucial for organic mineralization. Furthermore, Fe-NC-FJH exhibited robust catalytic activity across a broad pH range (≈3-11) and showed remarkable stability in degradation performance over three consecutive cycles. Lastly, three degradation pathways of quinoline, encompassing 22 intermediates, were proposed. The toxicity of these intermediates was evaluated using quantitative structure-activity relationship (QSAR) analysis, providing valuable insights into the environmental impact of the advanced oxidation process.