## 1 Introduction
One significant advantage of persulfate over traditional oxidants is its stability at neutral to slightly alkaline pHs, making it more versatile and suitable for a broader range of environmental conditions. Additionally, persulfate can be activated by a variety of methods, including UV light and transition metal catalysts, providing flexibility in process design. The combination of persulfate with UV light and iron-based materials can enhance the generation of sulfate radicals, resulting in more efficient pollutant degradation. Moreover, the use of persulfate reduces the need for continuous chemical replenishment, as its activation can be controlled more effectively, offering a more sustainable and cost-effective approach compared to conventional hydrogen peroxide-based systems. Additionally, the homogeneous nature of the classical process, where iron acts in solution, poses challenges such as catalyst recovery and potential iron leaching, which can complicate treatment and lead to secondary contamination. Furthermore, the efficiency of the classical photo-Fenton process can be affected by factors such as pH, where acidic conditions are required to maintain iron in its active ferrous state, limiting its applicability to a narrower range of environmental conditions [20]. To overcome these drawbacks, the use of heterogeneous catalysts such as Fe-based metal-organic frameworks (MOFs) and iron-rich minerals in the photo-Fenton process offers a promising alternative [20]. MOFs, often referred to as porous coordination polymers, are porous materials made of organic linkers and metal-containing nodes [21]. Fe-MOFs, with their high surface area, tunable pore structure, and ability to incorporate metal ions, have shown significant potential in enhancing the efficiency of the photo- Fenton process by providing a stable catalytic support, improving the activation of hydrogen peroxide or peroxydisulfate, and minimizing metal leaching. Fe-MOFs are one of the many documented MOFs with a wide range of catalytic uses across a broader pH range, including neutral or near-neutral conditions. Goethite (\(\alpha\)-FeOOH), a naturally abundant iron-bearing mineral, offers an eco-friendly and cost-effective alternative to homogeneous iron catalysts, providing a robust platform for heterogeneous Fenton reactions [22]. It exhibits a combination of properties essential for various applications, including resistance to photocorrosion, a wide operational pH range, and negligible iron leaching into the solution [23]. Additionally, it can serve as a source of iron and, consequently, as a catalyst in heterogeneous photocatalysis systems designed to facilitate photo-Fenton reactions [24]. Although there has been considerable advancement in the field of dye degradation, the use of photo-Fenton processes for the degradation of Nile Blue has not been thoroughly investigated. This specific dye poses distinct challenges, mainly because of its pH-dependent properties (pKa = 9.5) and the formation of reactive intermediates during the degradation process [25]. These complexities present an opportunity to further develop and improve advanced oxidation processes that are based on the photo-Fenton reaction. Furthermore, this study contributes a novel perspective by systematically evaluating the performance of two widely used oxidants--hydrogen peroxide and persulfate--applied separately but under identical conditions across both homogeneous (Fe\({}^{2+}\)) and heterogeneous (Basolite F300 and goethite) photo-Fenton systems. Notably, the application of goethite for persulfate activation under photo-Fenton conditions has not, to the best of our knowledge, been previously reported. This comparative analysis provides deeper mechanistic and performance-based insights into radical generation efficiency, mineralization potential, and operational sustainability--extending the current understanding beyond traditional single-cataly or single-oxidant approaches.