# Catalytic Advanced Oxidation Processes for Sulfamethoxazole Degradation
## 3 Results
### SMX and TOC Removal
SMX was not entirely removed by catalytic oxidation with H\({}_{2}\)O\({}_{2}\), and its concentration remained constant during the 3 h of reaction in the presence of TiO\({}_{2}\) and TiO\({}_{2}\)/CNT catalysts. The highest removals were achieved by the addition of CNT and Fe/CNT, removing approximately 50% of SMX after 3 h of reaction. Intermediates and ions were not detected in any reaction with H\({}_{2}\)O\({}_{2}\). The reduction profile of SMX concentration and TOC verified in the oxidation of H\({}_{2}\)O\({}_{2}\) with CNT and Fe/CNT was similar to adsorption on the CNT profile. Considering this similarity and the absence of intermediates in solution, it is possible that SMX removal, in this case, occurred due to adsorption and not by oxidation. However, when CNTs were combined with H\({}_{2}\)O\({}_{2}\), less removal was observed, probably due to competition between H\({}_{2}\)O\({}_{2}\) and SMX for the CNT active centers, reducing, therefore, the adsorption capacity of the catalyst [4; 26; 43]. In photocatalytic ozonation, as shown in Figure 2e,f, an improvement in the degradation of SMX was verified when compared to the non-catalytic process, except in the presence of TiO\({}_{2}\). The presence of CNT, Fe/CNT, and TiO\({}_{2}\)/CNT accelerated SMX degradation; however, after 15 min of reaction, SMX was completely degraded by all tested systems. The TOC removal results show that the highest mineralization occurred in the presence of CNT (93%), while the remaining reactions allowed 84% of TOC removal at the end of the reaction. Comparing the SMX degradation by photocatalytic ozonation with correspondent individual processes, photocatalysis, and catalytic ozonation, it is possible to observe that in the combined process carried out with CNT, SMX was degraded faster and higher mineralization was reached. This result demonstrates that the combination of radiation, O\({}_{3}\), and catalyst is beneficial for SMX degradation. The catalytic ozonation with H\({}_{2}\)O\({}_{2}\) was insensitive to the used catalyst, as shown in Figure 4. In the case of TOC removal, a fast mineralization rate was observed when Fe/CNT and TiO\({}_{2}\)/CNT were added, removing approximately 75% of the organic matter after 3 h of reaction. Moreover, catalytic ozonation with H\({}_{2}\)O\({}_{2}\) and TiO\({}_{2}\) presented higher TOC in solution than the non-catalytic process, probably because TiO\({}_{2}\) is not an ozonation catalyst. Figure 3: Dimensionless SMX (**a**) and TOC (**b**) concentration during H\({}_{2}\)O\({}_{2}\) catalytic oxidation and adsorption experiments (O\({}_{2}\)) on CNT, Fe/CNT, TiO\({}_{2}\), and TiO\({}_{2}\)/CNT. The mineralization of the SMX was not increased during catalytic ozonation and catalytic ozonation with H\({}_{2}\)O\({}_{2}\) in the presence of Fe/CNT catalyst, indicating that the addition of H\({}_{2}\)O\({}_{2}\) to ozonation is not advantageous under the operating conditions used. As previously mentioned, the H\({}_{2}\)O\({}_{2}\) added can adsorb on the catalyst surface and change its surface, reducing the available active centers and therefore decreasing the reaction as well as the formation of superficial radicals [5]. Furthermore, the amount of H\({}_{2}\)O\({}_{2}\) added to the system may not be enough, so it would be necessary to optimize the H\({}_{2}\)O\({}_{2}\) concentration and the pH of the solution to improve the results. The presence of H\({}_{2}\)O\({}_{2}\) in the photocatalytic reactions did not improve the SMX removal rates, as shown in Figure 4. However, except for the system with TiO\({}_{2}\), most of the catalytic systems had better performance in TOC removal than non-catalytic combinations. Although some studies show that the addition of H\({}_{2}\)O\({}_{2}\) to the photocatalysis with TiO\({}_{2}\) improves the process, this was not observed in this work probably due to the use of non-optimized H\({}_{2}\)O\({}_{2}\) concentration and pH [14; 39].