## 3 Results and Discussion
### CAF Degradation by Fenton Process  
The analysis of the Fenton technique specifically for caffeine degradation was conducted to explore its potential and enhance the method for future use in combined processes. This investigation assessed caffeine degradation in an aqueous solution using batch Fenton reaction experiments, varying the concentrations of H\({}_{2}\)O\({}_{2}\) and Fe\({}^{+2}\) at three levels (independent variables). The tests were analyzed using the response surface methodology, focusing on the response variables of C\({}_{\text{F}}\) and caffeine degradation. The Fenton reaction uses H\({}_{2}\)O\({}_{2}\) and iron ions as catalysts to generate reactive oxygen species that oxidize organic and inorganic compounds. The reaction mechanism (Equations (7)-(15) [30]) illustrates the oxidation of iron ions and the production of the desired hydroxyl radicals. Optimal conditions for the radical reactions include an acidic environment (pH below 3) to prevent iron precipitation and maintain catalyst activity,  
Figure 1: Response surfaces for R\({}_{\text{CAF}}\) and C\({}_{\text{F}}\) as function of pH and adsorbent dosage (**a,d**), pH and contact time (**b,e**), and adsorbent concentration and contact time (**c,f**). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Factor** & **Observed Minimum** & **Critical Values** & **Observed Maximum** \\ \hline pH & 3 & Natural (pH \(\sim\)6–8) & 11 \\ C\({}_{\text{ads}}\) (g L\({}^{-1}\)) & 1 & 10 & 10 \\ Contact time (min) & 10 & 116 & 120 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Critical values of adsorption experimental DOE. adequate concentrations of hydrogen peroxide to sustain radical formation, and controlled temperature and reaction time to enhance reaction rates. However, hydroxyl radicals can be eliminated by various means. The regeneration of iron ions indicates a cyclic mechanism, where iron acts as a catalyst. Equations (8)-(11) limit the reaction speed by consuming hydrogen peroxide and regenerating iron ions, while Equations (12)-(15) involve radical reactions. \[\text{Fe}^{+2}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{+3}+\text{OH}^{-}+ \text{-OH} \tag{7}\]  
\[\text{Fe}^{+3}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}^{+2}+\text{-O}_{2 }\text{H}+\text{H}^{+} \tag{8}\]  
\[\text{Fe}^{+2}+\text{-OH}\rightarrow\text{Fe}^{+3}+\text{OH}^{-} \tag{9}\]  
\[\text{Fe}^{+2}+\text{-O}_{2}\text{H}\rightarrow\text{Fe}^{+3}+\text{OH}_{2} ^{-} \tag{10}\]  
\[\text{Fe}^{+3}+\text{-O}_{2}\text{H}\rightarrow\text{Fe}^{+2}+\text{O}_{2}+ \text{H}^{+} \tag{11}\]  
\[\text{-OH}+\text{-OH}\rightarrow\text{H}_{2}\text{O}_{2} \tag{12}\]  
\[\text{-OH}+\text{H}_{2}\text{O}_{2}\rightarrow\text{-O}_{2}\text{H}+\text{H} _{2}\text{O} \tag{13}\]  
\[\text{-O}_{2}\text{H}+\text{-O}_{2}\text{H}\rightarrow\text{H}_{2}\text{O}_{2 }+\text{O}_{2} \tag{14}\]  
\[\text{-OH}+\text{-O}_{2}\text{H}\rightarrow\text{H}_{2}\text{O}+\text{O}_{2} \tag{15}\]  
Typically, an increase in Fenton reaction duration led to higher rates of caffeine degradation. Table 6 details the \(\text{C}_{\text{F}}\) and caffeine degradation results obtained through Fenton reactions for different concentrations of \(\text{H}_{2}\text{O}_{2}\) and \(\text{Fe}^{+2}\). The maximum degradation achieved was 98.92% in 60 min under conditions of 150 mg L\({}^{-1}\) of \(\text{H}_{2}\text{O}_{2}\) and 4 mg L\({}^{-1}\) of \(\text{FeSO}_{4}\text{7}\text{H}_{2}\text{O}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{\ \begin{tabular}{c} **H\({}_{2}\)O\({}_{2}\)** \\ **(mg L\({}^{-1}\))** \\ \end{tabular}  } & \multirow{2}{*}{
\begin{tabular}{c} **FeSO\({}_{4}\)** \(\cdot\)**\(\cdot\)This optimization was crucial to determine the maximum possible efficiency of caffeine degradation within the studied concentration ranges. Strategically, time points of 5 and 60 min were chosen for statistical analysis.