# 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
These results can be explained by the acceleration of the production of radical species (mainly hydroxyl radicals), the latter can reduce preferably Fe(III) sites on the catalyst surface when higher Fe\({}_{3}\)O\({}_{4}\) doses than 40 mg/L are added instead of degrading 4 EP and its intermediates. The reuse of the catalyst was tested by the collection of the solids by magnet and washing them several times with deionized water. The collected solids were heat treated at temperatures of 105, 180, 250, and 500 \({}^{\circ}\)C. Table 2 presents the results of heat treatment and the reuse of the catalyst in treating 100 mg/L 4 EP aqueous solutions using 1000 mg/L H\({}_{2}\)O\({}_{2}\), 40 mg/L reused catalyst at pH 3 and under 300 rpm stirring and room temperature. The increase of the temperature of the heat treatment decreased the mass of the catalyst, which can be explained by the dehydration and the release of volatile organics adsorbed on the surface of the catalyst with possible transformation of the catalyst by oxidation/reduction reactions in presence of air. In contrast, the increase of the heat treatment temperature enhanced TOC removal, which keep values higher than 64% for the treated catalyst. The same catalyst was collected, then treated at 500 \({}^{\circ}\)C, and reused in treating 4 EP aqueous solutions in the same conditions. TOC removals in the range of 83%-89% were measured indicating the good efficacy of the reused  
Figure 4: Influence of Fe\({}_{3}\)O\({}_{4}\) dose on TOC changes with time during the heterogeneous photo-Fenton treatment of 100 mg/L EP aqueous solutions. Experimental conditions: 1000 mg/L H\({}_{2}\)O\({}_{2}\), 0–100 mg/L Fe\({}_{3}\)O\({}_{4}\), pH 3, T = 25 \({}^{\circ}\)C, 300 rpm. catalyst. These results confirm the possible reuse of the solid catalyst for several times in heterogeneous photo-Fenton treatment of 4 EP in water. The efficacy of the Fenton and photo-Fenton processes in treating wastewaters containing organic pollutants depends largely on the production of hydroxyl radicals by chemical and photochemical decomposition of hydrogen peroxide [40; 41; 42]. H\({}_{2}\)O\({}_{2}\) is the main source of hydroxyl radicals even if little amount of OH\({}^{\bullet}\) can be formed by water photolysis. Consequently, the optimization of H\({}_{2}\)O\({}_{2}\) initial concentration ([H\({}_{2}\)O\({}_{2}\)]\({}_{0}\)) is fundamental to achieve a high production of hydroxyl radicals [18; 19; 20]. To examine the effect of H\({}_{2}\)O\({}_{2}\) initial concentration on the performance of the heterogeneous photo-Fenton process, aqueous solutions containing 100 mg/L 4 EP at pH 3.0 and 25 \({}^{\circ}\)C were treated by H\({}_{2}\)O\({}_{2}\) initial concentration in the range of 500-2000 mg/L. The dose of Fe\({}_{3}\)O\({}_{4}\) was calculated for each H\({}_{2}\)O\({}_{2}\) initial concentration from the mass ratio H\({}_{2}\)O\({}_{2}\)/Fe\({}_{3}\)O\({}_{4}\) fixed to 25. The results illustrated in Table 3 confirm that the efficiency of the heterogeneous photo-Fenton process depends on the H\({}_{2}\)O\({}_{2}\) initial concentration. The results of Table 1 showed that the TOC removal increased from 86% to 93%, then it decreased to 81% after 120 min of adding 500, 1000, and 2000 mg/L of H\({}_{2}\)O\({}_{2}\), respectively. The fact that the highest TOC removal was achieved with 1000 mg/L H\({}_{2}\)O\({}_{2}\) initial concentration is essentially due to the production of satisfactory amounts of HO\({}^{\bullet}\) radicals capable to mineralize most of the organic matter. Although, the increase of H\({}_{2}\)O\({}_{2}\) dose to higher than 1000 mg/L would theoretically result in a larger production of HO\({}^{\bullet}\) radicals, it did not result in an enhancement of the TOC removal.