## 3 Results and Discussion
### Electrochemical Behavior of CFTX in the Presence of Different Ions
#### 3.1.3 Electrolysis Assisted by UV-Vis Spectrophotometry  
Figure 3 displays the UV-Vis spectra of 0.025 g\(\cdot\)L\({}^{-1}\) CFTX aqueous solution in the presence of different 0.1 mol\(\cdot\)L\({}^{-1}\) NaX solutions (where X was one by one: F\({}^{-}\), Cl\({}^{-}\), Br\({}^{-}\), I\({}^{-}\)), at different electrolysis times. The CFTX spectrum shows two absorption peaks at 270 nm and 240 nm (Figure 3a) according to \(\pi\)\(\rightarrow\)\(\pi^{\star}\) and n\(\rightarrow\)n\({}^{\star}\) electronic transitions [18; 19; 30]. It can be observed that the CFTX has a different behavior in each individual solution. In the presence of fluoride anions, the intensities of the two absorption peaks present a slow  
Figure 2: CFTX UV-Vis spectra recorded before and after cyclic voltammetry (CV): (**a**) CFTX/sodium fluoride solution; (**b**) CFTX/sodium chloride solution; (**c**) CFTX/sodium bromide solution; (**d**) CFTX/sodium iodide solution.  
decreasing trend (Figure 3a) with increasing electrolysis time, suggesting that the CFTX is heterogeneously electrochemically degraded.  
During electrolysis, strong oxidized species are electrogenerated on platinum surface, such as XO\({}_{n}^{-}\) (X = Cl, Br, I; n = 1, 2, 3, 4), due to the electrooxidation of halide ions from supporting electrolyte. Consequently, there is a mediated electrooxidation by hydroxyl radicals electrogenerated from water decomposition and by XO\({}_{n}^{-}\) electrogenerated from supporting electrolyte [30; 32]. These oxy and oxy halogenated species can react both at the electrode surface and in the bulk of solution (indirect electrochemical degradation).  
As shown in Figure 3b,c, both absorption peaks decrease proportionally with the time. After 10 min and 5 min, respectively, these peaks are no longer detectable. As the intensity of absorbance maximum decreases, a new peak appears at 292 nm, in the Cl\({}^{-}\) presence (Figure 3b), and at 335 nm, in the Br\({}^{-}\) presence (Figure 3c) leading to the occurrence of a new chemical compound due to the oxygenated species of chlorine and bromine. The adsorption maximum of this compound increases over time, meaning that the peak is a consequence of multiple interactions and interferences between several compounds, which can occur from successive reactions between different species from the supporting electrolyte.  
On the other hand, two isosbestic points are registered (216 nm and 254 nm), being characteristic to an invariant absorbance transition from CFTX degradation to XO\({}_{n}^{-}\) electrogeneration. These results demonstrate the competitive interactions of CFTX molecules with oxy/oxyhalogenated species. Comparison between Figure 3b,c reveals a higher degradation degree of CFTX, in the presence of bromide ions than in the presence of chloride ions, suggesting that the oxybromides have a higher binding affinity.  
From Figure 3d, it is observed that a strong interaction of CFTX molecules with iodide ions take place. The spectrophotogram registered at initial time (t = 0 min) shows a small intensity peak at 270 nm, that could result from an overlapping of the CFTX spectrum and the iodine spectrum.  
Figure 3: UV-Vis spectra of CFTX recorded on platinum electrode, in solutions of sodium halides during constant current electrolysis: (**a**) CFTX/NaF solution; (**b**) CFTX/NaCl solution; (**c**) CFTX/NaBr solution; (**d**) CFTX/NaI solution.  
The data obtained from constant current density electrolysis sustain those provided by cyclic voltammetry, in the sense that in the presence of F\({}^{-}\), CFTX is gradually degraded for 60 min; in the presence of Cl\({}^{-}\) and Br\({}^{-}\), CFTX rapidly degradation, is followed by electrotransformation into other compounds; the effects of iodinated species are major, and the reaction medium composition is likely to be complex.