# 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 comparative experiments demonstrated the effectiveness of the heterogeneous photo-Fenton process in degrading 4 EP in water. However, taking into account the fact that the treatment of 4 EP by the heterogeneous photo-Fenton process aims to mineralize it into CO\({}_{2}\), H\({}_{2}\)O, and NO\({}_{3}\)\({}^{-}\) (or NH\({}_{4}\)\({}^{+}\)) or to transform it into easily biodegradable compounds, further experiments are needed to optimize the operating conditions targeting the integration of this method in larger applications than the lab scale. For that purpose, a series of experiments were conducted to examine the effects of some experimental parameters on the kinetic and the efficiency of the treatment of 4 EP synthetic wastewaters by UV/H\({}_{2}\)O\({}_{2}\)/ Fe\({}_{3}\)O\({}_{4}\) process. Initial pH, Fe\({}_{3}\)O\({}_{4}\) dose, and H\({}_{2}\)O\({}_{2}\) and 4 EP concentrations are the experimental parameters selected to be optimized to reach the highest yields of 4 EP degradation and mineralization. Fenton and photo-Fenton reactions are strongly pH-dependent as reported in the literature [40; 41; 42; 43]. Especially, it is well reported that the initial pH conditions significantly influence the production of hydroxyl radicals [20; 43; 44; 45; 46]. To examine the effect of initial pH on the treatment of aqueous solutions containing 100 mg/L of 4 EP by the heterogeneous photo-Fenton process, the initial pH values was varied in the range between 3 and 9 using 1000 mg/L H\({}_{2}\)O\({}_{2}\) and 40 mg/L Fe\({}_{3}\)O\({}_{4}\) at room temperature and a stirring rate under 300 rpm. The effect of the initial pH on TOC removal is given in Figure 3. This figure shows that TOC decreased from the beginning of the treatment for all initial pH values. The highest TOC removal was obtained at pH 3. Increasing pH from 3 to 5, to 7, and then to 9 decreased TOC removal. During the treatment of 4 EP aqueous solutions by the heterogeneous photo-Fenton process, TOC declined from 56 mg C/L to 2.1 mg C/L at pH 3.0, to 12.3 mg C/L at pH 5.0 and 17.5 mg C/L at pH 7.0 and 9.0 after 360 min. This indicates that more than 96% of TOC removal was achieved at pH 3.0, while TOC removals between 68% and 78% were calculated for the other initial pH values. The TOC removal during the treatment of 100 mg/L 4 EP aqueous solution using the homogeneous  
Figure 2: Kinetics of EP degradation (100 mg/L EP, at pH = 3, 25 \({}^{\circ}\)C, 300 rpm stirring) via: (-a-) the UV/H\({}_{2}\)O\({}_{2}\) process (H\({}_{2}\)O\({}_{2}\) = 1000 mg/L): (-\(\blacksquare\)-) the Fenton-like process ((Fe\({}_{3}\)O\({}_{4}\)= 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L)) and (-\(\blacklozenge\)-) the heterogeneous photo-Fenton process (Fe\({}_{3}\)O\({}_{4}\)= 40 mg/L and H\({}_{2}\)O\({}_{2}\) = 1000 mg/L). Inset: Pseudo-first-order kinetics plots. photo-Fenton process (UV/H\({}_{2}\)O\({}_{2}\)/Fe\({}^{2+}\): 1000 mg/L H\({}_{2}\)O\({}_{2}\), 10 mg/L Fe\({}^{2+}\) (similar amount of iron used with Fe\({}_{3}\)O\({}_{4}\))) achieved 98% at pH 3.0, 72% at pH 5.0, 56% at pH 7.0, and 37% at pH 9.0 after 360 min (data not shown here). These results demonstrated that the initial pH affects the efficiency of the treatment for both heterogeneous and homogeneous photo-Fenton processes; however, the lower effect on TOC removal was observed with the heterogeneous photo-Fenton. The difference between the heterogeneous and homogeneous photo-Fenton processes can be related to the slower regeneration of the homogeneous catalyst (Fe\({}^{2+}\)) at pH \(>\) 5 because of the precipitation of Fe(OH)\({}_{3}\). In addition, the decrease in the TOC removal in both the homogeneous and heterogeneous photo-Fenton processes could be due to the acceleration of auto-decomposition of H\({}_{2}\)O\({}_{2}\) leading to the lower production of hydroxyl radicals [20; 42; 43; 44; 45].