## 3 Results and Discussion
### Catalytic Activity of Dye in the Presence of AC/CFO  
The removal efficiency of dye under a variety of reaction conditions was investigated by varying the pH = 6.5, dye concentration of 50 mg/L, a catalyst dosage of 0.3 g/L, and SO\({}_{4}\) amount of 5 mM/L. The experimental results show that the RR198 degradation attained for PS, UV irradiation, CFO alone, PS/UV, and Fenton (AC/CFO activated with H\({}_{2}\)O\({}_{2}\)) after 25 min contact, was 18%, 22%, 34%, and 38%, respectively (Figure 4); the COD removal efficiencies were 15%, 20%, 30%, 33%, and 59%, respectively, under the same conditions, These results showed, low oxidation potential of PS alone for generation sulfate radicals. The free radical production increases in the presence of PS under UV irradiation as PS gets activated by UV to produce a powerful oxidant, SO\({}_{4}\)\({}^{\bullet}\), as the concentration of persulfate increased. However, PS would react with SO\({}_{4}\)\({}^{\bullet}\), leading to the decrease of SO\({}_{4}\)\({}^{\bullet}\) concentrations and hence the removal efficiency of dye did not change significantly. According to Figure 4, the removal efficiency attained by CFO was the higher than that of UV irradiation and PS, which are mainly due to the high oxidation capacity. However, this finding indicates that the oxidation of dye by these processes is rather limited [30; 40]. The highest removal efficiency of dye by AC, compared to that of oxidation processes, can be due to high specific surface area. When the AC/CFO nanocomposite was added, the removal of dye (79% in the reaction time of 50 min) changed significantly, indicating that the AC/CFO has much higher adsorption capacity for decolorization. The results show that increasing H\({}_{2}\)O\({}_{2}\) concentration does not improve oxidation capacity compared to persulfate (removal efficiency = 59%). This may be due to the abundance of hydrogen peroxide that plays a radical scavenger role. Additionally, the excess H\({}_{2}\)O\({}_{2}\) reacts with Fe\({}^{3+}\) to form hydroperoxyl radical which is weaker than hydroxyl radical. These results showed the synergistic effect between CFO and AC and the impregnation of CFO onto AC surface could cause an increase in dye removal by AC/CFO. In the reaction system of Fenton like catalyst (AC/CFO activated with PS), the removal efficiency of dye was 85.2% over 25 min. The high performance of this system is due to both, the adsorption and oxidation processes are involved in the removal efficiency of dye. Actually, results confirm that AC/CFO catalyst has a synergistic effect on PS for generation of sulfate radicals. When UV irradiation was (Equation (7)) added to the Fenton catalyst, the removal efficiency of dye was enhanced to much improved levels, 98.8% in the reaction time of 25 min. \[\text{S}_{2}\text{Os}^{2-}+\text{hv}\to 2\text{SO}_{4}\text{${}^{\bullet}$}. \tag{7}\]  
Based on these results, the catalytic ability of the PF like catalyst is higher than that of the typical Fenton like catalyst processes, which indicates that UV has high activating ability on PS which significantly enhanced the catalytic capacity of the AC/CFO nanocomposite. Therefore, this process overcomes problems typical of Fenton like catalysts. Excellent catalytic activity for the sulfate radical-based heterogeneous catalytic applications using cobalt ferrite (CoFe\({}_{2}\)O\({}_{4}\)), spinel ferrites, has been demonstrated due to its easy separation and high chemical stability. The additional AC/CFO nanocomposite led to the greater total surface area and number of active sites for PS activation to produce more SO\({}_{4}\)\({}^{\bullet}\) radicals. The generation of SO\({}_{4}\)\({}^{\bullet}\) radicals and the removal efficiencies of pollutants are increased under UV light irradiation in the photo-Fenton like process.