# Catalytic Degradation of 4-Ethylpyridine in Water by Heterogeneous Photo-Fenton Process
## 3 Results and Discussions
### Detailed Ontvestigations of the Degradation of 4 EP by the Heterogeneous Ohoto-Fenton Process
The analysis of iron leached from the Fe\({}_{3}\)O\({}_{4}\) solid catalyst is needed in this case to have an idea about the effect of the pH on the dissolution of iron during the treatment at different initial pH values. Table 1 illustrates the results of the analysis of iron by ICP-OES during the heterogeneous photo-Fenton treatment in the same conditions as Figure 3. The results show that small amounts of iron were measured in solution at neutral and alkaline media (0.63 and 0.14 mg/L at pH 7 and pH 9); however, 25% and 17% iron was dissolved at pH 3 and pH 5 (9.65 mg/L iron are contained in 40 mg/L Fe\({}_{3}\)O\({}_{4}\)) at the end of the treatment. Based on the data obtained in the present study, an initial pH between 3.0 and 5.0 can achieve higher TOC removal than 75% using the heterogeneous photo-Fenton process with less than 20% of the iron being leached from the Fe\({}_{3}\)O\({}_{4}\) solid catalyst. \begin{table}
\begin{tabular}{c c c c c} \hline
**Time** & **pH = 3.0** & **pH = 5.0** & **pH = 7.0** & **pH = 9.0** \\ \hline
0 min & 0.08 mg/L Fe & 0.05 mg/L Fe & ND & ND \\
60 min & 0.58 mg/L Fe & 0.19 mg/L Fe & 0.05 mg/L Fe & 0.01 mg/L Fe \\
120 min & 1.96 mg/L Fe & 1.43 mg/L Fe & 0.11 mg/L Fe & 0.02 mg/L Fe \\
180 min & 2.13 mg/L Fe & 1.51 mg/L Fe & 0.45 mg/L Fe & 0.05 mg/L Fe \\
360 min & 2.37 mg/L Fe & 1.62 mg/L Fe & 0.63 mg/L Fe & 0.14 mg/L Fe \\ \hline \end{tabular}
\end{table} 
Table 1: Analysis of dissolved iron during the treatment of 100 mg/L EP aqueous solutions by the heterogeneous photo-Fenton using 40 mg/L Fe\({}_{3}\)O\({}_{4}\) and 1000 mg/L H\({}_{2}\)O\({}_{2}\) at pH 3 under 300 rpm stirring and 25 \({}^{\circ}\)C.  
Figure 3: Influence of initial pH on TOC changes with time during heterogeneous photo-Fenton treatment of 100 mg/L EP aqueous solutions. Experimental conditions: 1000 mg/L H\({}_{2}\)O\({}_{2}\), 40 mg/L Fe\({}_{3}\)O\({}_{4}\), pH 3–9, T = 25 \({}^{\circ}\)C, 300 rpm. The catalyst dose is considered as a determining parameter for the production of radical oxidant species from the H\({}_{2}\)O\({}_{2}\) decomposition (Equations (1) and (3)) [44; 45; 46]. Iron(II)/Iron(III) in solid form or in solution are excellent catalysts to decompose H\({}_{2}\)O\({}_{2}\) efficiently into hydroxyl radicals HO\({}^{\bullet}\). The dose of the catalyst should be carefully adjusted to achieve high degradation yields and avoid the formation of stable iron(II)/(III) organic complexes. To evaluate the effect of the Fe\({}_{3}\)O\({}_{4}\) catalyst, some experiments of heterogeneous photo-Fenton treatment of 100 mg/L 4 EP synthetic wastewater were carried using a fixed H\({}_{2}\)O\({}_{2}\) concentration of 1000 mg/L at pH 3, and varying the dose of Fe\({}_{3}\)O\({}_{4}\) in the range from 0 to 100 mg/L at room temperature. The changes of TOC with time at different doses of Fe\({}_{3}\)O\({}_{4}\) are presented in Figure 4. These results display that the TOC decreased with time for all Fe\({}_{3}\)O\({}_{4}\) doses from the beginning of the treatment. The addition of Fe\({}_{3}\)O\({}_{4}\) catalyst accelerated the TOC decay compared to the experiment in its absence. The increase of Fe\({}_{3}\)O\({}_{4}\) concentration up to 40 mg/L improved the kinetics and the efficiency of the heterogeneous photo-Fenton process (87% and 96% TOC removals were calculated for 20 and 40 mg/L Fe\({}_{3}\)O\({}_{4}\), respectively). However, higher doses of Fe\({}_{3}\)O\({}_{4}\) than 40 mg/L decreased the efficiency of the degradation of 4 EP by heterogeneous photo-Fenton process in terms of TOC removal. Using 80 and 100 mg/L Fe\({}_{3}\)O\({}_{4}\) resulted in 85% and 74% TOC removals, respectively. It can be concluded that the most rapid TOC decay and the highest TOC removal were obtained with 40 mg/L Fe\({}_{3}\)O\({}_{4}\).