# Electrochemical Degradation of Crystal Violet Using Ti/Pt/SnO\({}_{2}\) Electrode
## 1 Introduction  
The protection of the environment and the problem of cleaning up contaminated water and soil require a rapid response worldwide. Pollution is often of agricultural or industrial origin because of the discharge of untreated effluents into the natural environment. The growth of industrial activities increases obviously the pollution sources [1, 2, 3, 4]. The textile industry is one of the industrial poles, it produces an enormous quantity of waste loaded with non-biodegradable dye stuffs [5, 6, 7, 8]. These discharges contribute to the degradation of the quality of surface water and groundwater by their harmful and toxic side effects [9, 10, 11]. Dyes, widely used in the textile industry, are widespread pollutants [12, 13]. The annual world production of dyes is about 7 \(\times\) 10\({}^{5}\) tons, of which 5-10% is discharged into water by the textile industry [14]. They can be carcinogenic and toxic and their intensive use in everyday life can have harmful consequences on the environment and food [15, 16, 17]. Most of the dyes used are synthetic products, with an often-complex molecular structure, whichmakes them stable and difficult to degrade by conventional treatment processes [18; 19]. Thus, the implementation of treatment means adapted to this type of pollution is necessary in order to reduce its impact on the ecosystem. However, preventive effluents from the textile and processing industries must be treated at source before discharge into the environment. There are several physical methods that can be used to treat polluted effluents such as coagulation, flocculation, membrane filtration, ion exchange, adsorption. The main disadvantage of these processes is that they create waste that must then be treated or incinerated. The advanced oxidation processes generate in-situ, of the strongest oxidant--the hydroxyl radical. This radical can be efficient but very often it requires the addition of chemical reagents. Thanks to the electrochemical generation of hydroxyl radicals from water oxidation, the electro-oxidation process is promising because it can be used for all types of effluents, it is compatible with environmental applications because the electrode is the only reagent used [20; 21; 22; 23; 24; 25; 26; 27]. The simplicity of the equipment and the ease of use, the low cost of construction, the absence of sludge production, the mineralization of pollutants and the progression of the reaction by the electron are among the advantages of the electro-oxidation process [28; 29; 30; 31]. The electrochemical oxidation of species in aqueous solutions can be carried out either by the transfer of electrons or by the transfer of oxygen atoms; alternatively, both pathways can be taken simultaneously. Direct electrochemical oxidation is heterogeneous: electron exchange occurs between organic species and the electrocatalytic electrode surface. Indirect oxidation uses an electrogenerated mediator. Indeed, a strong oxidant is generated at the anode and reacts chemically with the organics. The action of this oxidant can either occur close to the electrode surface if the oxidant is very reactive and not stable (i) the case of hydroxyl radical electrogenerated by water oxidation (Equation (1)), or in the bulk if the oxidant is sufficiently stable to diffuse into the solution (the case of active chlorine). \[M+H_{2}O\to M(HO^{{}^{\prime}})+H^{+}+e^{-} \tag{1}\]  
The in-situ production of oxidants presents various advantages: (i) in certain cases, complete mineralization can be reached, and reuse of the solution can be considered; (ii) in other cases, the action of the oxidant overcomes the limitations of mass transfer for the treatment of dilute solutions. The presence or the deliberate addition of Cl\({}^{-}\) in a solution to be treated by electrochemical oxidation can accelerate the process of organic matter degradation. Indeed, the organic matter can be oxidized at the electrode and also at the center of the solution by chemical reaction with the active chlorine. For example, [PERSON] et al.