From electric field accelerated generation of SO₄^-·/·OH radicals to rapid mineralization of gatifloxacin: The role of Fe@Fe-UP@NCA activated persulfate induced free radicals

The performance of Fe@Fe-UP@NCA catalyst for electro assisted degradation of gatifloxacin (GAT) in salt containing wastewater was studied. In order to achieve higher degradation efficiency of three dimensional electrochemical reactor (3DER), based on previous research, the Fe@Fe-UP@NCA/3DER system was assembled using high specific surface area Fe@Fe-UP@NCA particles as particle electrodes, and the influence of operating parameters on the catalytic degradation of organic pollutants such as GAT was studied. Under the optimal process parameters, after 6 min of reaction, the removal rates of GAT, COD, and TOC obtained were 81.39 %, 71.74 %, and 55.65 %, respectively. The concentration change of GAT conforms to the quasi first order kinetic equation, with a kinetic constant of 0.0887 min⁻¹ and an energy consumption of only 71.09 kWh/kg GAT. During the catalyst regeneration cycle, it was found that after 6 cycles of degradation of GAT wastewater, the GAT removal rate only decreased by 0.26 %. In addition, XRD, SEM-EDS, FT-IR, Raman and XPS characterization showed that the rich pore structure, high specific surface area, and abundant surface multi metal atom catalytic active sites enable peroxymonosulfate (PMS) molecules to be affected by the rich and poor electron centers on the NCA surface, decomposing to produce active components with strong catalytic oxidation performance, such as ·OH and SO₄^-·, which can achieve the fracture and mineralization of organic pollutants in a short period of time. This can be confirmed by electron paramagnetic resonance (EPR) spectroscopy. Due to the fact that the N₄-Fe-O-Fe-N₄ coordination (four coordination unit) center was the essential structure of Fe@Fe-UP@NCA surface metal atoms, and the unsaturated Fe coordination content was high, the degree of ligand defects was large, and the metal atoms have a higher density, thus exhibiting excellent catalytic performance. Further inference of the degradation mechanism and pathway of GAT was made through liquid chromatography-mass spectrometry (LC-MS) assistance: under electric field enhancement, electron migration and valence state conversion between metal ions promote PMS activation and the rapid occurrence of Fenton-like reaction, forming ·OH and SO₄^-· that continuously attack GAT. By replacing or removing oxygen-containing functional groups, the GAT structure was broken, generating many intermediate products, and ultimately fully mineralized into inorganic substances such as CO₂, H₂O, NO₃^– and F^-. This study provides new technical support for activating PMS to degrade organic pollutants in saline wastewater using easily recyclable catalysts.