# Removal of Methylene Blue by Metal Oxides Supported by Oily Sludge Pyrolysis Residues
## 3 Results and Discussion
### Characterization of Composite Materials
#### 3.2.2 Composition Characterization of Composite Materials XRD  
X-ray diffraction of the pyrolysis residue and AC-CuO, AC-ZnO, and AC-TiO\({}_{2}\) are shown in Figure 6. It can be seen that the characteristic diffraction peaks of CuO appeared near 35\({}^{\circ}\), 38\({}^{\circ}\), 49\({}^{\circ}\), and 66\({}^{\circ}\) in AC-CuO, and the peaks at 61\({}^{\circ}\) and 68\({}^{\circ}\) were stronger than those of the pyrolysis residue. After removal of methylene blue, the characteristic diffraction peaks remained relatively stable. The characteristic diffraction peaks of ZnO (characteristic diffraction peaks near 32\({}^{\circ}\), 34\({}^{\circ}\), 36\({}^{\circ}\)) and TiO\({}_{2}\) (characteristic diffraction peaks near 25\({}^{\circ}\), 37\({}^{\circ}\), 48\({}^{\circ}\)) appeared on AC-ZnO and AC-TiO\({}_{2}\), respectively, indicating that AC-ZnO and AC-TiO\({}_{2}\) were successfully prepared.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Source**} & **Specific** & **Micropore** & **Mesopore** & **Total Pore** & **Mesopore** & **Total Pore** \\  & **Surface Area** & **Volume** & **Volume** & **Volume** & **Average Pore** & **Average Pore** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **Diameter** & **Diameter** \\  & **S\({}_{\text{BET}}\)** & **V\({}_{\text{mic}}\)** & **V\({}_{\text{mes}}\)** & **V\({}_{\text{tot}}\)** & **(mm)** & **D\({}_{\text{P}}\)** \\ \hline AC-CuO & 5.9082 & 0.0014 & 0.0208 & 0.0222 & 16.6842 & 14.6344 \\ \hline AC-ZnO & 4.9138 & 0.0012 & 0.0204 & 0.0216 & 19.6171 & 17.1305 \\ \hline AC-TiO\({}_{2}\) & 7.8951 & 0.0001 & 0.0834 & 0.0837 & 15.8715 & 15.6531 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specific surface area and pore volume of the composite materials.  
Figure 5: Pore size distribution curves of (**a**) AC-CuO; (**b**) AC-ZnO; and (**c**) AC-TiO\({}_{2}\).  
FT-IR  
The FT-IR analysis of pyrolysis residue and AC-CuO, AC-ZnO, and AC-TiO\({}_{2}\) are shown in Figure 7. It can be seen that the -OH absorption peak and C = C stretching vibration absorption peak of the pyrolysis residue presented at 3421 and 1638 cm\({}^{-1}\), respectively, indicating that there were hydroxyl and C = C functional groups on the surface of the residue. There were two absorption peaks at 872 and 613 cm\({}^{-1}\), indicating the existence of meta-disubstituted aromatic hydrocarbons on the surface of the pyrolysis residue. The absorption peak near 471 cm\({}^{-1}\) may have been caused by the mineral composition in the sludge ash [35]. Compared with that in the pyrolysis residue, the -OH absorption peak of the composite materials weakened due to the supported metal oxide. Among them, the characteristic peaks of CuO, ZnO, and TiO\({}_{2}\) presented were between 410 and 610 cm\({}^{-1}\)[36], 400 and 600 cm\({}^{-1}\)[37], and 400 and 1000 cm\({}^{-1}\)[38], respectively, indicating that AC-CuO, AC-ZnO, and AC-TiO\({}_{2}\) were successfully prepared.  
Figure 8 shows the XPS images of AC-CuO, AC-ZnO, and AC-TiO\({}_{2}\), respectively. High-resolution XPS spectra of Cu 2p, Zn 2p, and Ti 2p demonstrated the presence of prominent Cu, Zn, and Ti peaks in the composite materials, respectively, indicating that CuO, ZnO, and TiO\({}_{2}\) had been attached to the pyrolysis residue.  
Figure 6: XRD patterns of pyrolysis residue; (a) AC-CuO; (b) AC-ZnO; and (c) AC-TiO\({}_{2}\).  
Figure 8: XPS spectra of (**a**) AC-CuO; (**b**) AC-ZnO; and (**c**) AC-TiO\({}_{2}\).  
Figure 7: FT-IR images of residue carrier; (**a**) AC-CuO; (**b**) AC-ZnO; and (**c**) AC-TiO\({}_{2}\).