## 3 Results and Discussion
### Effects of Operational Parameters Photo-Fenton like Catalyst
#### 3.3.2 Effect of Catalyst Dosage  
The effect of catalyst dosage on RR198 and COD removal was investigated at a constant PS = 5 mM/L, reaction time 25 min, and at pH 6.5 (Figure 6).  
The increase in AC/CFO dosage from 0.1 to 0.3 g/L enhanced the adsorptive removal of dye. When the AC/CFO dosage was 0.3 g/L, the removal efficiency of dye increased to 99% and COD removal to 97.2%. In PF like catalyst the irradiation of ultraviolet promotes the generation and the release of Fe\({}^{2+}\) into the solution from the AC/CFO surface resulting in the reduction of the catalyst loading and enhancing the catalytic capacity of the catalyst in the presence of PS. Additionally, the increase of catalyst dosage results in an increased number of active sites of the catalyst for the activation of PS to generate sulfate radicals. Therefore, the increased addition of AC/CFO, achieves higher removal efficiency of dye.  
The holes in the CoFe\({}_{2}\)O\({}_{4}\) valence band can be used as oxidizing agents in the removal of dye. Therefore, the recombination of photo-generated electrons and holes (e/h) can enhance the photocatalytic activity of the nanocomposites and hybrids (Equations (9) and (10)). With enhancement of e/h, as increasing AC/CFO enables, the photocatalytic activity of the hybrids enhances further. The S\({}_{2}\)O\({}_{4}\) is considered to have two functions in the photocatalytic process, it accepts a photogenerated electron to form sulfate radicals. The produced electron/hole enables oxidation and reduction processes to occur that electrons on the CFO surface of photocatalyst react with S\({}_{2}\)O\({}_{8}\) to produce highly active SO\({}_{4}\)\({}^{\bullet}\). Effective separation of the photogenerated electron/hole pairs at the composite photocatalyst interface lead to increased rates of photocatalytic activity. These holes (h+) and sulfate radicals, being strong oxidizing agents, can mineralize organic contaminants completely. As a result, the combination  
Figure 6: Effect of catalyst dose on RR198 and COD removal efficiency, optimum conditions: [RR198= 25 mg/L, PS = 5 mM/L, reaction time: 25 min, and pH= 6.5].  
of AC/CFO-PS can effectively enhance the rate of photocatalytic depolarization and shorten the removal time for dyes in wastewater.  
\[\text{CoFe}_{2}\text{O}_{4}+\text{hv}\rightarrow\text{CoFe}_{2}\text{O}_{4}\ ( \text{h}+\text{e}) \tag{9}\]  
\[\text{CoFe}_{2}\text{O}_{4}\ (\text{e})+\text{S}_{2}\text{O}_{4}\rightarrow\text{ CoFe}_{2}\text{O}_{4}+\text{SO}^{4\bullet} \tag{10}\]  
The excessive dosages of catalyst could remove \(\text{SO}_{4}{}^{\bullet-}\) radicals without reacting with contaminants, due to the reaction of PS for either producing \(\text{SO}_{5}{}^{\bullet-}\) or recombining the formation of \(\text{S}_{2}\text{O}_{8}{}^{2-}\)[44]. Therefore, these results show that ferrous ion present in catalyst is an active agent in degradation of dye using PS activation [34; 45]. However, the removal efficiency of RR198 was not changed significantly when the dosage of AC/CFO increased from 0.3 to 0.7 g/L; only slight increment in removal efficiency was discerned, although the sulfate radicals would be generated more quickly with further 0.3 g/L dosage of AC/CFO (Equation (11)).  
\[\text{SO}_{4}{}^{\bullet-}+\text{SO}_{4}{}^{\bullet-}\rightarrow\text{S}_{2} \text{O}_{8}{}^{2-} \tag{11}\]  
Moreover, scavenging effects of \(\text{SO}_{4}{}^{\bullet-}\) in the presence of excessive iron ions (Equations (12) and (13)) reduce the active sites of catalyst at higher dosages due to formation of self-binding and aggregates of iron ions in AC/CFO.  
\[\text{SO}_{4}{}^{\bullet-}+\text{Fe}^{2+}\rightarrow\text{Fe}^{3+}+\text{SO} _{4}{}^{2-} \tag{12}\]  
\[\text{Fe}\ (\text{OH})^{2+}+\text{hv}\rightarrow\text{Fe}^{2+}+\text{SO} _{4}{}^{2-}. \tag{13}\]