## 3 Results and Discussion
### Reactive Oxygen Species During PMS Activation
Additionally, TP-187 and TP-129 undergo further oxidation of the -NH2 group to form -NO2, while TP-114 is generated by the oxidation of the -CH3 group in TP-99 to -CHO. The non-radical selectivity of these reactions makes them highly reactive toward electron-rich groups such as sulfonamides. Most of the degradation products are formed by the oxidation of groups on the sulfonamide. Notably, the coupling product TP-503, resulting from the formation of an N=N bond between two SMX molecules, was detected in the system [67]. Figure 10 illustrates several major degradation pathways of SMX, which can be broadly categorized into hydrogen substitution, oxidation, and coupling. In conclusion, the possible mechanism in the FeCo-LDH/PMS system was pro-posed as follows: In the current study, there are three main pathways for the generation of the non-radical species \({}^{1}\)O2, which are the autodecomposition of peroxymonosulfate [68], the reaction between O2\({}^{-}\)- and -OH [69], and the disproportionation of O2\({}^{-}\)- [70]. In the EPR test experiments and quenching experiments in the paper, we confirmed that O2\({}^{-}\)- is indeed present in the system, but not -OH, so the reaction between O2\({}^{-}\)- and -OH is ruled out first. Secondly, in the PMS-only system, we detected the presence of \({}^{1}\)O2 by EPR, so there may be a generation pathway by deprotonated autolysis of peroxymonosulfate [71] (Equation (1)). The presence of O2\({}^{-}\)- and the further generation of \({}^{1}\)O2 in the system after addition of the catalyst suggests that there may be the disproportionation of O2\({}^{-}\) (Equation (2)). The octahedral coordination geometry in LDHs' layered structure enables facile incorporation of multivalent cobalt (Co2\({}^{+}\)/Co3\({}^{+}\)) and iron (Fe2\({}^{+}\)/Fe3\({}^{+}\)) species, permitting reversible redox cycling without structural degradation. Thermodynamic evaluations through standard reduction potentials (Equation (3)) reveal energetically favorable elec  
Figure 10: Possible degradation pathways of SMX. tron transfer between Co(II) and Fe(III) redox couples [72]. Fe(III) sites in FeCoLDH first coordinated with the O atoms in PMS and formed [Fe(III)OOSO3]\({}^{+}\) complexes (Equation (4)) [60]. The major active \(\equiv\)FeIV=O species were formed from the heterolytic cleavage of O-O in [Fe(III)OOSO3]+ complexes, and since the presence of SO4 was not found within the system, the complex cleavage may need to be carried out with a reducing substance, which, based on the properties of the material, is likely to be divalent Fe or Co [73; 74]. \[{\rm{HSO}_{5}}^{-}+{\rm{SO}_{5}}^{2-}\rightarrow{\rm{HSO}_{4}}^{-}+{\rm{SO}_{4} }^{2-}+{{}^{1}}{\rm{O}_{2}} \tag{1}\]  
\[2{\rm{O}_{2}}^{\bullet-}+2{\rm{H}_{2}}{\rm{O}}\rightarrow{{}^{1}}{\rm{O}_{2}} +{\rm{H}_{2}}{\rm{O}_{2}}+2{\rm{OH}}^{-} \tag{2}\]  
\[{\rm{Fe}^{3+}}+\ {\rm{Co}^{2+}}\rightarrow{\rm{Fe}^{2+}}+\ {\rm{Co}^{3+}};\ {\rm{E}^{0}}=\ 1.04\ {\rm{V}} \tag{3}\]  
\[{\rm{Fe(III)}}+{\rm{HSO}_{5}}^{-}\rightarrow\ [{\rm{Fe(III)OOSO}_{3}}]^{+}+{ \rm{H}}^{+} \tag{4}\]  
\[{\rm{[Fe(III)OOSO}_{3}]}^{+}+{\rm{Fe}^{2+}}/{\rm{Co}^{2+}}\rightarrow{\rm{Fe( IV)}}={\rm{O}}+{\rm{Fe}^{3+}}/{\rm{Co}^{3+}}+{\rm{SO}_{4}}^{2-} \tag{5}\]