## 3 Results and Discussion
### Photocatalytic Degradation
However, a decrease in efficiency was observed for Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) after the first cycle, possibly due to the blocking of active sites by contaminants, structural degradation, or morphological changes. In contrast, the FeWO\({}_{4}\) sample exhibited a more stable performance across cycles, reinforcing its robustness and reusability. This behavior may be attributed to its porosity and the absence of well-defined crystalline facets, which likely contribute to a more accessible and resilient catalytic surface. In a study evaluating FeWO\({}_{4}\) nanorods as a photo-Fenton catalyst for methylene blue removal, the catalyst maintained its performance over multiple cycles [35], consistent with the results observed in the present work using heterogeneous photocatalysis. Similarly, Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) was investigated as a catalyst for persulfate activation in the degradation of bisphenol A, where a slight decrease in activity was reported over successive cycles [36], also aligning with our findings. These comparisons suggest that, among the two iron-based catalysts, FeWO\({}_{4}\) exhibits superior reusability, while Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) shows a modest decline in performance, which could be attributed, for instance, to differences in the morphology achieved during synthesis. To better understand the catalyst performance, TOC analysis was conducted. It was observed that over both cycles, Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) removed 60 \(\pm\) 7% of the organic content from the effluent, while FeWO\({}_{4}\) achieved 67 \(\pm\) 0.7% mineralization. This result suggests the degradation of additional organic compounds present in the effluent that do not absorb at the same wavelength (616 nm) as the monitored dye. While both catalysts demonstrated  
Figure 4: (**A**) Removal of color and (**B**) recycling of the catalyst. Conditions: 50 mg catalyst and 100 mL effluent, without pH adjustment. similar color removal efficiencies, the superior and consistent performance of FeWO\({}_{4}\) across cycles was evident. In contrast, the 7% deviation observed for Fe\({}_{2}\)(MoO\({}_{4}\))\({}_{3}\) may indicate a decline in catalytic activity over time. These findings underscore the importance of catalyst morphology in determining performance during real effluent treatment. Since photocatalytic activity is strongly influenced by factors such as particle size, geometry, and morphology, the enhanced performance of FeWO\({}_{4}\) can be attributed to its porous, high-surface-area morphology, as confirmed by FE-SEM analysis and PL spectroscopy. An additional advantage of the proposed process using simple iron-based oxides is the ability to treat the real effluent directly. In contrast, other studies highlight the need for pre-treatment--biological or physicochemical--before applying an advanced oxidation process [37]. Although such steps can enhance organic removal, pre-treatment was not required in this study, given the initial TOC levels. The degradation of real effluents poses a significant challenge due to their complex and variable composition, which may include mixtures of dyes, chemical additives, and various organic and inorganic compounds, depending on the source. Given the heterogeneous nature of such effluents, proposing a specific photocatalytic degradation mechanism becomes difficult. For example, the presence of chloride species in the medium can reduce the removal efficiency, as Cl\({}^{-}\) ions can act as scavengers of hydroxyl radicals [38]. These hydroxyl radicals are among the reactive oxygen species (ROS) typically generated during the heterogeneous photocatalysis process. After light-induced generation of e\({}^{-}\)/h\({}^{+}\) pairs, the holes (electron vacancies) in the VB can react with surface-bound water to produce hydroxyl radicals, whereas the electrons in the CB can reduce oxygen to generate superoxide radical anions [39].