# Pilot-Scale Fenton-like System for Wastewater Treatment Using Iron Mud Carbon Catalyst
## 3 Results and Discussion  
### Characterizations of Catalyst  
To investigate the specific surface area, pore volume, and diameter of FSC, FSC was analyzed by the N\({}_{2}\) adsorption-desorption isotherm. As demonstrated in Figure 2a, the N\({}_{2}\) adsorption-desorption isotherm of both fresh and used catalysts presents a typical H3-type hysteresis loop (IUPAC classification), and the curve exhibits obvious adsorption-desorption separation in the region with high relative pressure (P/P\({}_{0}\) > 0.4), indicating that there is a large amount of mesoporous structure formed by particle accumulation in the material. The aperture distribution map of fresh catalysts shows that the aperture distribution presents a dual-mode feature. The proportion of micropores (<2 nm) is less than 5%, and the mesoporous pore size of 10-20 nm contributes 68.3% of the total pore volume, which is \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Index** & **COD/mg\(\cdot\)L\({}^{-1}\)** & **SS/mg\(\cdot\)L\({}^{-1}\)** & **TN/mg\(\cdot\)L\({}^{-1}\)** & **NH\({}_{3}\)-N/mg\(\cdot\)L\({}^{-1}\)** & **TP** & **pH** \\ \hline Inflow & 70 & 220 & 40 & 8 & 5 & 6–7.5 \\ Outflow & 40 & 5 & 10 & 1.0 & 0.2 & 6–9 \\ \hline \end{tabular}
\end{table} 
Table 1: Sewage indicators of the sewage treatment plant. highly consistent with the characteristics of mesoporous pore proportion of high-efficient catalysts [21]. In addition, the pore volume attenuation trend in the large pore region (-50 nm) conforms to the power law distribution. Therefore, FSC has a hierarchical pore structure, which is conducive to the mass transfer and diffusion of pollutant molecule [22]. Compared with fresh catalysts, micropores of used catalysts almost disappear. Mesoporous region decreases by 30%, while the macroporous region exhibits relatively insignificant changes. In addition, it was found by BET calculation that the SSA, average pore size, and total pore volume of FSC were 32.21 m\({}^{2}\)/g, 9.94 nm, and 0.0949 cm\({}^{3}\)/g, respectively. The used catalyst showed decreased SSA (21.46 m\({}^{2}\)/g) and total pore volume (0.784 cm\({}^{3}\)/g). Its average pore diameter slightly increased to 10.04 nm. The changes resulted from pollutant adsorption and pore blockage. Figure 2b shows the microscopic morphology of FSC. The results show that FSC has an irregular particle shape, an obvious porous structure on the surface, and an uneven, rough, and layered texture, which is conducive to promoting the mass transfer process and improving the reaction efficiency between oxidants and pollutants. In order to explore the changes in FSC surface functional groups before and after the reaction, FTIR spectroscopy was used to analyze FSC. As shown in Figure 2c. The unused FSC showed a strong O-H stretching vibration peak at 3403 cm\({}^{-1}\), indicating that the surface of FSC is rich in hydroxyl functional groups, which can promote H\({}_{2}\)O\({}_{2}\) activation by providing H\({}^{+}\)[23]. The characteristic peak of O=C-O at 1520 cm\({}^{-1}\) corresponds to the ester group or carboxyl group, and the peak of C=O at 1427 cm\({}^{-1}\) indicates the presence of carbonyl group. It has been confirmed that the C=O structure promotes the formation of \({}^{1}\)O\({}_{2}\). The strong C-O/Si-O stretching vibration peak at 1023 cm\({}^{-1}\) involves both C-O bond in the organic ligand and Si-O bond as a carrier, which jointly affect the electronic structure and active site distribution of the catalyst. In addition, the characteristic peaks at 875 cm\({}^{-1}\) (S-O) and 523 cm\({}^{-1}\) (Fe-O) correspond to the vibration of sulfur-containing functional  
Figure 2: (**a**) Nitrogen adsorption–desorption isotherm (illustrated as aperture distribution map of FSC), (**b**) SEM images of fresh FSC, (**c**) FTIR spectra, and (**d**) XRD pattern of fresh and used FSC. groups and ferro-oxygen bonds, respectively.