## 3 Results and Discussion
### Electro-Fenton-like Tests
#### 3.3.2 Effect of Catalyst Dosage  
After verifying the effective catalytic activity of the ZnO/g-C\({}_{3}\)N\({}_{4}\) composites in the electro-Fenton-like process, a series of experiments were carried out to investigate whether increasing or decreasing the catalyst dosage could improve the degradation efficiency. The behavior of the system was studied by testing three different amounts of catalyst, 25, 50, and 75 mg while maintaining a constant initial dye concentration constant (10 mg/L). The results obtained, shown in Figure 7c, indicated that, as the amount of catalyst increased, degradation showed a decreasing trend at the same reaction times, and when the amount of catalyst decreased, the opposite occurred.  
Although after ending the treatment, the degradation achieved in the three cases was very similar, 98.93, 99.21, and 97.01%, respectively, when analyzing each of the other treatment times, it was observed that, with the amount of 25 mg, the degradation obtained was greater. For example, after 30 min of treatment, the degradations achieved were 77.61, 67.53, and 56.30% for 25, 50, and 75 mg, respectively. The degradation followed pseudo-first-order kinetics in all cases, and the kinetic constants obtained (Figure 7d) showed the same trend. In Figure 7d, it can be clearly seen how the value of the kinetic constant increased as the amount of composites used decreased. This is similar to the behavior observed in the photo-Fenton-like treatment, where an increase in the catalyst-H\({}_{2}\)O\({}_{2}\) molar ratio led to an improvement in the degradation process. Considering the H\({}_{2}\)O\({}_{2}\) generated,  
Figure 7: Results of Rhodamine B degradation experiments by different treatments and conditions: (**a**) profiles of Rhodamine B degradation obtained from anodic oxidation and electro-Fenton like at 25 mA; (**b**) EC values and apparent pseudo-first-order constant constants obtained for anodic oxidation and electro-Fenton like after 90 min of treatment at 25 mA; (**c**) profiles of Rhodamine B using different dosages of ZnO/g-C\({}_{3}\)N\({}_{4}\) composites; (**e**) profiles of Rhodamine B degradation using successive cycles. Dashed lines depict the pseudo-first-order kinetic fitting for all experiments with an R\({}^{2}\) > 98%. (**b,d,f**) Apparent pseudo-first-order constant (k) values for each experiment.  
the catalyst-H2O2 molar ratios in the electro-Fenton-like treatment for 25, 50, and 75 mg of catalyst were 1:0.05, 1:0.027, and 1:0.013. So, the improvement as the ratio increases was also observed in the electro-Fenton-like process, although the mechanisms involved are different. In this case, the worsening of degradation could be due to the occurrence of side reactions that modify the mechanisms of the Fenton-like reaction. The secondary reactions would result in the production of other radicals such as hydroperoxyl radicals with lower oxidizing power than \(\cdot OH\) radicals [19; 65; 66; 67; 68].  
The results obtained with the optimum amount of catalyst were compared with other studies already carried out in order to analyze the feasibility of using the synthesized material as a catalyst for the electro-Fenton process. In the case of [PERSON] et al. [69], a 97.20% degradation of Rhodamine B was achieved after 1 h of treatment using Fe/Cu kaolin particles (30 g/L) as a catalyst. [PERSON] et al. [70] reached a degradation of 97.30% of Rhodamine B after 3 h of treatment using Fe3O4 (0.1 g/L) as a catalyst. The degradation achieved in this manuscript, in proportion to the amount of catalyst used in the treatment, was higher. Therefore, it can be concluded that the synthesized material is presented as a viable, competitive, and promising alternative for the degradation of dyes by electro-Fenton treatment.