# Electrochemical Degradation of Crystal Violet Using Ti/Pt/SnO\({}_{2}\) Electrode
## 3 Results and Discussion
### Influence of Operating Parameters  
#### 3.2.1 Effect of the Presence of Chloride Ions  
The effect of the NaCl concentration on CV oxidation was studied under the following conditions, a concentration of \(10\) mg L\({}^{-1}\) CV, initial pH = 7 and at a current density of \(50\) mA cm\({}^{-2}\).  
Figure 3: Cyclic voltammetry curve on an Ti/Pt/SnO\({}_{2}\) electrode, with a scan rate of \(1\) V s\({}^{-1}\).  
Figure 4a shows the temporal removal of CV using different concentrations of electrolytes (Na\({}_{2}\)SO\({}_{4}\) and NaCl). It also appears that the initial rate of the CV removal (or decolorization) during electrochemical treatment is much higher as the NaCl concentration increases, due to the reactions between the generated chlorinated species and CV.  
In fact, one can notice that after a 30 min treatment time, the rate reached a value of 91% for a sodium chloride concentration of 0.01 M NaCl + 0.1 M Na\({}_{2}\)SO\({}_{4}\), 95% at 0.03 M NaCl + 0.1 M Na\({}_{2}\)SO\({}_{4}\), 96% at 0.05 M NaCl + 0.1 M Na\({}_{2}\)SO\({}_{4}\), and 98% for the 0.1 M NaCl + 0.1 M Na\({}_{2}\)SO\({}_{4}\) concentration. However, after 2 h of treatment, a percentage of 100% was observed for the concentrations 0.01 M, 0.03 M, 0.05 M NaCl electrolyte.  
However, in the absence of the latter, i.e., 0 M NaCl + 0.1 M KNO\({}_{3}\), the decolorization reaches only 16%. Chlorides can react with hydroxyl radicals at the anode to form hypochlorous acid or hypochlorite ions, depending on the pH, according to the Equations (5)-(7).  
\[Cl^{-}+HO^{-}\to ClO^{-}+H^{+}+e^{-} \tag{5}\]  
\[Cl^{-}+HO^{-}\to HClO+e^{-} \tag{6}\]  
\[HClO\to ClO^{-}+H^{+} \tag{7}\]  
A large amount of active chlorine in the solution due to the presence of chloride ions accelerated the indirect oxidation process of the wastewater loaded with organic matter and consequently the degradation process of the crystal violet dye was increased. A synergy of two processes takes place: oxidation by hydroxide radicals and oxidation by electrogenerated active chlorine  
In order to evidence the CV degradation by active chlorine, the following experiment has been carried out: a solution containing only 0.05 M NaCl was prepared, and then this solution was electrolyzed during 40 min by applying a current density of 40 mA cm\({}^{-2}\), then the polarization was stopped and crystal violet was added and the absorbance was monitored over time. At the end, we noticed that the decolorization is almost total after only 30 min of electrolysis. The latter experience highlights that the main reaction to decolorize the solution is the chemical reaction between the active chlorine (generated electrochemically) and the CV.  
In addition, Figure 4b shows that increasing the concentration of the electrolytes leads to a decrease in the operating voltage at the given current density and thus a decrease in the energy consumption.  
Figure 4: (**a**) Effect of NaCl concentration on degradation of the CV solution; (**b**) chronopoteniograms during electrolysis of the CV solution ([CV]\({}_{0}\) = 10 mg L\({}^{-1}\), initial pH = 7, i = 50 mA cm\({}^{-2}\) and temperature = 25 \({}^{\circ}\)C).