# Catalytic Degradation of 4-Ethylpyridine in Water by Heterogeneous Photo-Fenton Process
## 3 Results and Discussions  
Comparative Performance of H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\), UV/H\({}_{2}\)O\({}_{2}\), and UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) Processes  
In order to highlight the importance of combining the Fenton-like process and UV irradiation, the performance of single and combined processes, including UV irradiation, H\({}_{2}\)O\({}_{2}\) oxidation (H\({}_{2}\)O\({}_{2}\) = 1000 mg/L), Fe\({}_{3}\)O\({}_{4}\) adsorption (Fe\({}_{3}\)O\({}_{4}\) = 40 mg/L), H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) (Fe\({}_{3}\)O\({}_{4}\) = 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L), UV/H\({}_{2}\)O\({}_{2}\), and UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) (Fe\({}_{3}\)O\({}_{4}\) = 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L) in treating 4 EP aqueous solutions were compared. Figure 1 presents 4 EP removals from 100 mg/L 4 EP aqueous solutions at pH 3 using the single and combined processes over 60 min. For the single processes (UV irradiation, H\({}_{2}\)O\({}_{2}\) oxidation, Fe\({}_{3}\)O\({}_{4}\) adsorption), 4 EP removals did not exceed more than 6% indicating the slowness of the reactions involved in the elimination of 4 EP from water. UV irradiation alone does not have enough energy to rupture all the chemical bonds in 4 EP molecules. Fe\({}_{3}\)O\({}_{4}\) active adsorption surface sites adsorb only a few 4 EP molecules because of its low specific area. Even H\({}_{2}\)O\({}_{2}\) oxidation showed a higher 4 EP removal compared to the two other single processes (UV irradiation and Fe\({}_{3}\)O\({}_{4}\) adsorption), its power is not sufficient to oxidize large 4 EP molecules in water. However, combined processes showed higher 4 EP removals than single processes. The heterogeneous photo-Fenton (UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\)) process achieved the highest 4 EP removal of 95%, however, the Fenton-like (H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\)) and UV/H\({}_{2}\)O\({}_{2}\) processes removed 65% and 43% 4 EP from water within 60 min. For further investigations of 4 EP degradation kinetics using the combined processes, the changes of 4 EP concentration with time are plotted and presented in Figure 2 for each of the combined processes. This figure shows that the 4 EP concentration declined with time for all combined processes indicating the degradation of 4 EP molecules. The highest 4 EP removals were measured after 120 min, 180 min, and 360 min for the heterogeneous photo-Fenton (99%), Fenton-like (95%), and UV/H\({}_{2}\)O\({}_{2}\) (94%) processes, respectively. The degradation of 4 EP in water by each of the combined processes follows pseudo-first-order kinetics as confirmed by the linear plots of Ln[4 EP]\({}_{0}\)/[4 EP]\({}_{t}\) vs. time (inset of Figure 2). Pseudo-first-order rate constants of 0.007 min\({}^{-1}\), 0.02 min\({}^{-1}\), 0.05 min\({}^{-1}\) are calculated for UV/H\({}_{2}\)O\({}_{2}\), Fenton-like, and heterogeneous photo-Fenton  
Figure 1: The percent of EP removal at the end of the treatment of 100 mg/L EP aqueous solutions at pH = 3, and 25 \({}^{\circ}\)C, under 300 rpm stirring by UV irradiation, Fe\({}_{3}\)O\({}_{4}\) (40 mg/L) adsorption, H\({}_{2}\)O\({}_{2}\) (1000 mg/L) oxidation, UV/H\({}_{2}\)O\({}_{2}\) process (H\({}_{2}\)O\({}_{2}\) = 1000 mg/L), Fenton-like process (Fe\({}_{3}\)O\({}_{4}\) = 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L), and the heterogeneous photo-Fenton process (Fe\({}_{3}\)O\({}_{4}\) = 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L). processes, respectively. These results demonstrate that heterogeneous photo-Fenton process is more rapid and more efficient than UV/H\({}_{2}\)O\({}_{2}\) and Fenton-like processes in degrading 4 EP in water.