## 3 Results and Discussion
### Characterization of Fenton Iron Peat Catalyst
In addition, the relative contents of the active sites obtained from Figure 4 are displayed in Figure 5. As shown in Figure 3a, the C 1s spectrum was fitted into four characteristic peaks, including C=C/C-C (284.7 eV), C-N/C-O (285.5 eV), C=O (286.5 eV), and O-C=O (288.8 eV) [17]. According to Figure 4a, the relative content of C=O in Cat\(-\)1, Cat\(-\)2, Cat\(-\)3, Cat\(-\)4, and Cat\(-\)5 was 5.46%, 5.27%, 8.41%, 5.87%, and 6.25%, respectively, indicating an initial increase followed by a decrease with prolonged pyrolysis time. The Cat\(-\)3 catalyst has the fewest carbon sites, which is not conducive to activating the oxidant. Therefore, the activity of the Cat\(-\)3 catalyst is not high. All experiments in this study were repeated three times. As depicted in Figure 4b, the N 1s spectrum exhibited three characteristic peaks corresponding to pyridinic-N (398.5 eV), pyrrolic-N (399.8 eV), and graphitic-N (400.8 eV) [18]. The proportion of pyridinic-N remained relatively stable (\(-\)0.6%) across different pyrolysis times, suggesting minimal influence of pyrolysis duration on its content. As shown in Figure 5b, the relative content of pyrrolic-N initially decreased from 0.37% to 0.08% as the pyrolysis time increased from 1 h to 3 h. As the pyrolysis time increased from 1 h to 3 h, the pyrrolic-N content decreased from 0.37% to 0.08%, followed by a slight increase to 0.17% at 5 h. The content of graphitic-N showed little variation with pyrolysis time, increasing only slightly from 1.2% at 1 h to 1.3% at 5 h.  
Figure 4: XPS spectra of (**a**) C1s, (**b**) N1s, (**c**) O1s, and (**d**) Fe2p in Cat\(-\)1, Cat\(-\)2, Cat\(-\)3, Cat\(-\)4 and Cat\(-\)5. Figure 4c shows that the O 1s spectrum was deconvolved into five peaks: Fe-O (530.1 eV), adsorbed oxygen (O\({}_{\text{ads}}\), 530.66 eV), C=O (531.3 eV), O-C=O (532.0 eV), and C-O (533.0 eV) [19]. The Fe-O component represents lattice oxygen bonded to Fe in the iron sludge, while O\({}_{\text{ads}}\) corresponds to surface-adsorbed oxygen species such as O\({}^{-}\) or O\({}_{2}\)\({}^{-}\) According to Figure 5c, the relative content of Fe-O in Cat\(-\)1, Cat\(-\)2, Cat\(-\)3, Cat\(-\)4, and Cat\(-\)5 was 4.67%, 5.73%, 5.71%, 5.53%, and 3.85%, respectively. The Fe 2p spectrum was deconvoluted into Fe(II), Fe(III), metallic Fe\({}^{0}\), and satellite peaks. The characteristic peaks at 711.0 eV and 724.7 eV correspond to Fe 2p\({}_{3/2}\) and Fe 2p\({}_{1/2}\), respectively. Further deconvolution revealed that the peaks at 710.6 eV and 724.3 eV were associated with Fe(II), while those at 712.4 eV and 726.0 eV were attributed to Fe(III) [20]. Additionally, satellite peaks for Fe(II) and Fe(III) were observed at 717.8 eV and 732.7 eV, respectively. As shown in Figure 5d, the Fe content in Cat\(-\)1, Cat\(-\)2, Cat\(-\)3, Cat\(-\)4, and Cat\(-\)5 was 4.71%, 4.34%, 4.73%, and 4.33%, respectively, indicating that pyrolysis time had little effect on the total Fe content. However, at a pyrolysis time of 2 h, Cat\(-\)2 exhibited the highest Fe\({}^{0}\) content (0.64%), which is favorable for H\({}_{2}\)O\({}_{2}\) activation and organic pollutant degradation.