# Optimization of Organic Content Removal from Aqueous Solutions by Fenton-Ozonation
## 3 Results
### Fenton-Pervzone Process
The evolution of the apparent rate constant (\(k_{app}\)) is consistent with the observed order of process efficiency: Fe-L27 + O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) > Fe-L27 + O\({}_{3}\) > L27 + O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) > O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) > L27 + O\({}_{3}\) > O\({}_{3}\) alone. Mineralization results (Figure 7c,d) reveal substantial differences among the tested processes. Complete mineralization (100%) is achieved after 60 min with the Fe-L27 + O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) and Fe-L27 + O\({}_{3}\) systems, whereas the other processes exhibit significantly lower efficiencies (Figure 7d). These findings highlight the key catalytic role of iron, especially in its Fe\({}^{2+}\) oxidation state, in promoting the generation of hydroxyl radicals. A non-exhaustive set of reactions contributing to OH\({}^{\circ}\) production is presented below [28; 39; 40; 41]:  
\[\rm{O_{3}}\,+\,2,4-D\,\rightarrow\,Products \tag{11}\]  
\[\rm{O_{3}}\,+\,HO^{-}\,\rightarrow\,HO^{\circ}+\left(O_{2}^{-}\leftrightarrows \,HO_{2}^{-}\right) \tag{12}\]  
\[\rm{H_{2}O_{2}}\,\leftrightarrows\,HO_{2}^{-}\,+\,H^{+} \tag{13}\]  
\[\rm{HO_{2}^{-}+O_{3}}\,\rightarrow\,O_{2}+HO^{\circ}+O_{2}^{-} \tag{14}\]  
\[\rm{Fe^{2+}+H_{2}O_{2}}\,\rightarrow\,Fe^{3+}\,+\,HO^{\circ}+HO^{-} \tag{15}\]  
\[\rm{H_{2}O_{2}}\,+\,HO^{\circ}\,\rightarrow\,H_{2}O\,+\,HO_{2}^{\circ} \tag{16}\]  
\[\rm{Fe^{2+}}\,+\,HO^{\circ}\,\rightarrow\,Fe^{3+}\,+\,HO^{-} \tag{17}\]  
Figure 6:0  
Figure 6:1  
Figure 6:2  
Figure 6:3  
Figure 6:4  
Figure 6:5  
Figure 6:6  
The results shown in Figure 8 highlight the beneficial impact of incorporating iron-enriched carbon-based catalytic materials (L27-Fe) into advanced oxidation processes (AOPs), particularly in enhancing the degradation and mineralization efficiencies of 2,4-D. This improvement is not merely the additive effect of ozone, hydrogen peroxide, and activated carbon used separately, but rather the result of a synergistic interaction between these three components. This synergy promotes a greater generation of hydroxyl radicals, enabling more extensive oxidation of the 2,4-D molecule. Furthermore, thermogravimetric analyses of the activated carbons after 60 min of 2,4-D treatment via the different AOPs \begin{table}
\begin{tabular}{c c c c c c} \hline  & \(\bf{Y_{HPLC}^{J(min)}}\) (\%) & \(\bf{Y_{TOC}^{J(min)}}\) (\%) & \(\bf{Y_{HPLC}^{J(min)}}\) (\%) & \(\bf{Y_{TOC}^{J(min)}}\) (\%) & \(\bf{k_{app}}\) (\(\bf{min^{-1}}\)) \\ \hline O\({}_{3}\) & 69 & 22 & 100 & 33 & 0.12 \\ O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) & 89 & 30 & 100 & 52 & 0.23 \\ L27 + O\({}_{3}\) & 86 & 44 & 100 & 61 & 0.18 \\ L27 + O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) & 97 & 63 & 100 & 77 & 0.31 \\ Fe-L27 + O\({}_{3}\) & 99 & 84 & 100 & 100 & 0.49 \\ Fe-L27 + O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) & 100 & 72 & 100 & 100 & 0.71 \\ \hline \end{tabular}
\end{table} 
Table 8: Degradation and mineralization rate of 2,4-D at 10 min and 60 min according to different AOPs. (Figure 8) provide evidence of slight residual adsorption. Following a simple adsorption process on L27, for example, a distinct thermal desorption peak of 2_A_-D is observed at 334 \({}^{\circ}\)C (Figure 8a), indicating substantial molecular adsorption onto the carbon material. In contrast, this desorption peak is nearly absent for samples treated with AOPs, suggesting that 2,4-D was largely degraded rather than merely adsorbed. A small residual desorption signal remains visible, particularly on L27 treated with O\({}_{3}\) + H\({}_{2}\)O\({}_{2}\) (red curve in Figure 8b), which may indicate partial adsorption or incomplete degradation under certain conditions. These findings support the conclusion that under AOP conditions, L27 and Fe-L27 function primarily as catalytic supports for oxidant activation rather than as passive adsorbents.