## 1 Introduction  
The extensive use of synthetic dyes in industrial applications, including textiles, cosmetics, leather processing, and biotechnology, has emerged as a significant environmental challenge in recent decades [1]. These compounds, characterized by their chemical stability and resistance to conventional biological treatment methods, demonstrate remarkable persistence in aquatic environments [2, 3]. Epidemiological studies have linked prolonged exposure to synthetic dyes with an increase in respiratory disorders and a significant elevation in thyroid dysfunction cases among textile industry workers [4, 5]. Additionally, a series of scientific reports showed that certain azo and aze dyes can cause tumor development in different animal species (mainly rats) [6; 7; 8]. Repeated inhalation of dyes can also cause various disorders, such as damage to the liver, nervous system, thyroid problems, and tissue necrosis [9; 10]. Nile Blue (C\({}_{20}\)H\({}_{20}\)N\({}_{3}\)O-Cl), an azine dye with a complex heterocyclic structure, presents particular challenges due to its high water solubility, resistance to photodegradation, and tendency to form stable complexes with metal ions in aqueous solutions [11; 12]. These properties not only enhance its persistence in the environment, but also complicate conventional treatment approaches. Apart from health issues, the intense color of water imparted by dyes inhibits the access of sunlight to the interior of aqueous bodies and, thus, limits the photosynthesis process of aquatic plants, putting aquatic species at risk [5; 13]. There are many different treatment methods used for the removal of dyes. These include conventional methods such as biological processes, membrane filtration, coagulation/flocculation, precipitation, and adsorption, as well as electrochemical and photocatalytic methods [14]. Biological methods often face limitations in treating dyes due to the antimicrobial characteristics of these compounds, which hinder removal efficiencies. Other conventional methods have also the main drawback of low removal efficiencies. Conversely, Advanced Oxidation Processes (AOPs) demonstrate a remarkable efficacy across diverse domains, including environmental applications [15], medical treatment, energy production, and organic synthesis [16]. Among AOPs, the photo-Fenton process is recognized for its ability to produce high reactive hydroxyl radicals (\({}^{\bullet}\)OH, E\({}^{\circ}\) = 2.8 V) along with other oxidative species, facilitating the transformation of organic pollutants into fully mineralized forms [17; 18], as illustrated as follows (Equations (1) and (2)):  
\[\text{Fe}^{2+}+\text{H}_{2}\text{O}_{2}\rightarrow\text{Fe}(\text{OH})^{2+}+ \text{HO}^{\bullet} \tag{1}\]  
\[\text{Fe}(\text{OH})^{2+}+\text{hv}\rightarrow\text{Fe}^{2+}+\text{HO}^{\bullet} \tag{2}\]  
The classical photo-Fenton process, employing iron (Fe) as a catalyst and hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) as an oxidant, has demonstrated considerable success in environmental remediation [18]. However, alternative modifications and catalysts have been explored to enhance the process's efficiency, reduce costs, improve pollutant degradation under milder conditions, and alter several limitations that hinder its widespread application. One major limitation is the rapid decomposition of hydrogen peroxide, which requires continuous replenishment to maintain high radical generation, leading to higher operational costs. On the other hand, persulfate (S\({}_{2}\)O\({}_{8}\)\({}^{2-}\)) has emerged as a promising alternative oxidant in advanced oxidation processes due to its unique ability to generate reactive oxygen species (ROS) such as sulfate radicals (\({}^{\bullet}\)SO\({}_{4}\)\({}^{-}\)) upon activation [19]. These sulfate radicals are highly reactive and can effectively degrade a wide range of organic contaminants, including those resistant to hydroxyl radicals.