# 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
This may be due to the consumption of HO\({}^{\bullet}\) radicals by excessive amounts of H\({}_{2}\)O\({}_{2}\) (Equation 5 and 6) and the acceleration of H\({}_{2}\)O\({}_{2}\) disproportion into O\({}_{2}\) and H\({}_{2}\)O (Equation (7)) [43; 44; 45; 46; 47; 48]:  
\[\mathrm{HO^{\bullet}+H_{2}O_{2}\to H_{2}O+HO_{2}^{\bullet}} \tag{5}\]  
\[\mathrm{HO^{\bullet}+HO_{2}^{\bullet}\to H_{2}O+O_{2}} \tag{6}\]  
\[2\mathrm{H_{2}O_{2}\to 2H_{2}O+O_{2}} \tag{7}\] \begin{table}
\begin{tabular}{c c c} \hline
**Heat Treatment** & **Mass Collected** & **\% TOC Removal** \\
**(240 min)** & **(mg/L)** & **(360 min)** \\ \hline T = 105 \({}^{\circ}\)C & 36.2 & 64 \\ T = 180 \({}^{\circ}\)C & 33.6 & 70 \\ T = 250 \({}^{\circ}\)C & 32.4 & 76 \\ T = 500 \({}^{\circ}\)C & 30.3 & 89 (85/87/84/86) \\ \hline \end{tabular}
\end{table} 
Table 2: Results of the reuse of the catalyst during the treatment of 100 mg/L EP aqueous solutions by the heterogeneous photo-Fenton using 40 mg/L treated catalyst and 1000 mg/L H\({}_{2}\)O\({}_{2}\) at pH 3 under 300 rpm stirring and 25 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{c c c} \hline
**[H\({}_{2}\)O\({}_{2}\)]\({}_{0}\) (mg/L)** & **[EP]\({}_{0}\) (mg/L)** & **\% TOC Removal** \\ \hline
500 & 100 & 86 \\
1000 & 100 & 93 \\
2000 & 100 & 81 \\
1000 & 50 & 92 \\
1000 & 100 & 93 \\
1000 & 200 & 84 \\ \hline \end{tabular}
\end{table} 
Table 3: Influence of H\({}_{2}\)O\({}_{2}\) and EP concentrations on TOC removal during the treatment by the heterogeneous photo-Fenton process (UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\)) during 120 UV irradiation at pH 3 and under 300 rpm stirring and 25 \({}^{\circ}\)C.  
To evaluate the effect of 4 EP initial concentration on the efficiency of the heterogeneous photo-Fenton process, pH and temperature were fixed at 3 and 25 \({}^{\circ}\)C, and the mass ratio H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) and H\({}_{2}\)O\({}_{2}\)]/4 EP were maintained constant and equal to 25 and 10, respectively. The 4 EP initial concentration was varied in the range of 50-200 mg/L (see Table 3). Increasing 4 EP initial concentration from 50 to 100 mg/L increased TOC removal from 87% to 93% after 120 min; while increasing the 4 EP initial concentration from 100 to 200 mg/L decreased TOC removal to 84%. This is mainly due to the smaller production of radical species limited by H\({}_{2}\)O\({}_{2}\) concentration and Fe\({}_{3}\)O\({}_{4}\) dose for low 4 EP initial concentrations and to the absorption of UV light by 4 EP molecules when high 4 EP initial concentrations are treated. Figure 5a shows 4 EP and TOC (in mg C/L) decay with time during the treatment of 100 mg/L 4 EP aqueous solution by the heterogeneous photo-Fenton process using 1000 mg/L H\({}_{2}\)O\({}_{2}\), 40 mg/L Fe\({}_{3}\)O\({}_{4}\) at pH 3 under 300 rpm stirring and room temperature. As it can be seen, 4 EP and TOC concentrations decline with time with different rates. As it can be observed, 4 EP decay is more rapid than TOC indicating 4 EP degradation into intermediates without CO\({}_{2}\) release, which undergoes several oxidation steps to mineralize at the end of the treatment. The UV-VIS absorption spectra plotted in Figure 5b confirm the opening of the pyridine ring by the disappearance of the band located at 260 nm after 60 min. HPLC analysis detected the formation of 4-pyridone and 4-hydroxypyridine as aromatic intermediates and maleic and oxalic acids as aliphatic intermediates. Figure 5c presents the changes of the peak area of each intermediate with time during the heterogeneous photo-Fenton treatment of 100 mg/L 4 EP aqueous solution. 4-hydroxypyridine and 4-pyridone were formed at the beginning of the treatment and disappeared within 30 min. Maleic acid was detected during the first 60 min, while oxalic acid was accumulated during the treatment. These results confirm the formation of aromatic intermediates, which undergo an opening of the pyridine ring to form aliphatic carboxylic acids (maleic acid and formic acid).