## 3 Results and Discussion
### Degradation of HCQ by BDD-Electrolysis in Real Water Matrices  
The elimination of HCQ (Figure 3a) and organic matter (Figure 3b), in terms of COD, in polluted river water sample (\(\approx\)26.87 mg L\({}^{-1}\)) by EO approach with BDD electrode is shown in Figure 3. In order to compare \(j\), the electrolysis experiments for removing HCQ using BDD 1 Ti reactor were performed by applying 15, 30 and 45 mA cm\({}^{-2}\) in order to comprehend the effect of this experimental condition. As shown in Figure 3a, normalized changes of HCQ concentration were registered and a complete HCQ decay was attained, for all \(j\) values. A faster HCQ elimination was achieved when an increase on the \(j\) was reached. This behavior can be attributed to the increase on the production of the oxidants that are typically \({}^{\bullet}\)OH radicals (5), SO\({}_{4}\)\({}^{-\bullet}\)(6) and S\({}_{2}\)O\({}_{8}\)\({}^{2-}\)(7,8) [33; 34], promoting a quick oxidation of HCQ in the polluted river water matrix. BDD electrode is considered a non-active anode material that can produce efficiently free heterogeneous \({}^{\bullet}\)OH radicals at its surface [33] as  
Figure 2: Results obtained for determining HCQ in river water by the standard additions method using the DPV approach with a cork-graphite sensor (\(\blacklozenge\)) standard additions of 1 mM HCQ in 0.1 M H\({}_{2}\)SO\({}_{4}\) (200, 400 and 600 mL) as well as (\(\blacklozenge\)) river water sample. well as other oxidants [11], which contribute to quickly mineralizing/degrading organics in synthetic and real water matrices [35,36]. \[\text{BDD}+\text{H}_{2}\text{O}\rightarrow\text{BDD}(\text{$ \bullet$}\text{OH})+\text{H}+\text{e} \tag{5}\] \[\text{SO}_{4}{}^{-}+\text{BDD}(\text{$\bullet$}\text{OH}) \rightarrow\text{SO}_{4}{}^{-\bullet}+\text{H}_{2}\text{O}\] (6) \[\text{SO}_{4}{}^{-\bullet}+\text{SO}_{4}{}^{-\bullet} \rightarrow\text{S}_{2}\text{O}_{8}{}^{2}\] (7) \[\text{2 SO}_{4}{}^{2-}\rightarrow\text{S}_{2}\text{O}_{8}{}^{2-}+ \text{2e}^{-} \tag{8}\]  
In fact, polarization curves (Figure 4) and cyclic voltammetry (inset in Figure 4) have confirmed this information. Figure 4 shows the linear polarization curves of (a) non-polluted and (b) polluted river water matrices with BDD anode at 50 mV s\({}^{-1}\) as scan rate. The curves (a and b) are very different and show that oxygen evolution potential starts at +1.85 V versus Ag/AgCl (3 M) when non-polluted water was investigated. This means that BDD anode has high oxygen evolution overpotential in real water matrix, and consequently, it is a poor electrocatalysts for the oxygen evolution reaction (o.e.r.) compared with other electrodes reported in literature [37,38]. Meanwhile, polluted river water sample presented a well-defined peak at about +1.6 V before the o.e.r and it moderately extends to +1.9 V where the production of free heterogeneous \(\bullet\)OH radicals [33] and other oxidants [11] is feasible. This result clearly indicated that direct and indirect oxidations can be attained, allowing a quick elimination of HCQ from real polluted water matrix [39]. Figure 3: Effect of \(j\): (\(\bullet\)) 15, (\(\bullet\)) 30 and (\(\bullet\)) 45 mA cm\({}^{-2}\) on the abatement of 26.8 mg L\({}^{-1}\) of HCQ in an acidic river water matrix with H\({}_{2}\)SO\({}_{4}\): (**a**) normalized HCQ concentration decays ([HCQ]\({}_{1}\)/[HCQ]\({}_{0}\) at time t and t = 0 (in min) considering an initial HCQ concentration of 26.87 mg L\({}^{-1}\), as electroanalytically determined by DPV approach with cork-graphite sensor at 25 \(\pm\) 2 \({}^{\circ}\)C). Inset: Decay kinetic analysis assuming pseudo-first order reaction. (**b**) COD decay, over time in min. Cyclic voltammograms were also obtained with (a) non-polluted and (b) polluted river water matrices with BDD anode, in acidic sample at 25 \({}^{\circ}\)C (inset in Figure 4).