# Catalytic Advanced Oxidation Processes for Sulfamethoxazole Degradation
## 3 Results  
### Catalyst Characterization  
The textural properties of the catalysts are presented in Table 2. The highest surface areas (S\({}_{\text{BET}}\)) were verified in CNT and Fe/CNT samples, but Fe/CNT has a slightly lower area due to iron impregnated on the surface of the CNT. On the other hand, TiO\({}_{2}\) has the lowest surface area and pore volume.  
The results of the XRD analysis for TiO\({}_{2}\) and TiO\({}_{2}\)/CNT are also shown in Table 2. The crystalline phases were identified by applying the Rietveld refinement. The crystal composition of TiO\({}_{2}\) is 93% of anatase and 7% of rutile, while TiO\({}_{2}\)/CNT contains 97% of anatase and 3% of rutile. The difference in  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Compound** & **Structure** & **Formula** & **M** & **LOD * (g mol\({}^{*}\))** & **r\({}^{2}\)** \\ \hline SMX & & C\({}_{10}\)H\({}_{11}\)N\({}_{3}\)O\({}_{3}\)S & 253.28 & 0.08 & 0.99989 \\ AMI & & C\({}_{4}\)H\({}_{6}\)N\({}_{2}\)O & 98.1 & 0.05 & 0.99998 \\ BZQ & & C\({}_{6}\)H\({}_{4}\)O\({}_{2}\) & 108.09 & 0.1 & 0.99984 \\ OXM & & C\({}_{2}\)H\({}_{3}\)NO\({}_{3}\) & 89.05 & 0.05 & 0.9995 \\ OXL & & C\({}_{2}\)H\({}_{2}\)O\({}_{4}\) & 90.03 & 0.5 & 0.99940 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of sulfamethoxazole (SMX) and intermediate compounds mentioned in this work.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **S\({}_{\text{BET}}\) (m\({}^{2}\) g\({}^{-1}\))** & **V\({}_{\text{P}}\) (p/p=0.95) (cm\({}^{3}\) g\({}^{-1}\))** & **\% Crystal Phase** & **Crystal Diameter (nm)** \\ \hline CNT & 262 & 0.556 & - & - \\ Fe/CNT & 252 & 0.689 & - & - \\ TiO\({}_{2}\) & 134 & 0.112 & Anatase 93\% & Anatase 8.91 \\  & & & Rutile 7\% & Rutile 14.7 \\ TiO\({}_{2}\)/CNT & 142 & 0.164 & Anatase 97\% & Anatase 14.6 \\  & & & Rutile 3\% & Rutile 40.7 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Textural properties of the prepared catalysts and crystal properties of TiO\({}_{2}\) and TiO\({}_{2}\)/carbon nanotube (CNT) samples.  
crystal percentage between TiO\({}_{2}\) and TiO\({}_{2}\)/CNT probably occurs because of the method used in the mixing of catalysts, which can modify the TiO\({}_{2}\) crystal phase. The results show that the TiO\({}_{2}\)-based catalysts are formed by a higher percentage of anatase form which corresponds to the most active crystal for photocatalytic reactions.  
As expected, TGA analysis (results not shown) demonstrates that CNT and Fe/CNT have a higher mass loss due to the burning of carbon material during heating; furthermore, Fe/CNT has a lower mass loss due to the presence of iron. TiO\({}_{2}\) presents little mass loss, as expected since TiO\({}_{2}\) is thermodynamically stable and formed mainly by rutile and anatase crystals. The determined fractions of CNT and TiO\({}_{2}\) in the composite are 15% and 85%, respectively.  
TPR analysis of Fe/CNT under 5% of hydrogen flow determined the temperature of reduction of the metal. Two reduction peaks were observed--a first peak between 300 and 400 \({}^{\circ}\)C, where the metal is reduced to Fe\({}_{3}\)O\({}_{4}\), and a second peak between 400 and 600 \({}^{\circ}\)C, which corresponds to a sequential reduction of Fe\({}_{3}\)O\({}_{4}\) to FeO and Fe\({}^{0}\)[6]. TEM analysis, as shown in Figure 1, shows the presence of impregnated iron in the catalyst with uniform particle size and uniform metal distribution on the surface of the CNT.