For instance, activated carbon, zeolites, clay minerals, and other materials can be employed to adsorb chrysodine and methylene blue from water [24; 25; 26; 27; 28; 29; 30; 31; 32]. Chemical coagulation and flocculation are also alternatives [33; 34]. Membrane filtration techniques, such as reverse osmosis, nanofiltration, or ultrafiltration, can also effectively remove these dyes from water [35; 36; 37]. Nevertheless, all these methods involve the transference of the pollutant from one phase to another while leaving its molecular structure intact, retaining its potential risks. Certain microorganisms, however, possess the ability to biologically degrade dyes, and activated sludge processes or biofilters can be employed to remove chrysodine and methylene blue from water [38; 39; 40; 41]. Biological methods also have certain disadvantages, including specificity, slow degradation rates, sensitivity to environmental conditions, a need for nutrient supplementation, high operational costs, and the potential for the formation of harmful by-products [42]. Advanced oxidation processes (AOPs), such as ozonation, photocatalysis, or Fenton's reagent, contribute to overcoming most of these inconveniences, as AOPs generate highly reactive hydroxyl radicals that break down the dye molecules into simpler and less toxic compounds. Ideally, complete mineralization of the pollutants into CO\({}_{2}\) and water can be achieved. Nanoscale Zero-Valent Iron (nZVI) is commonly used in advanced oxidation processes as a catalyst to facilitate the degradation of pollutants [43; 44; 45]. Due to its high surface area and ability to generate large quantities of reactive oxygen species (ROS) such as hydroxyl radicals (-OH), nZVI exhibits increased reactivity towards a wide variety of pollutants, including organic contaminants [43; 44], heavy metals [46], and certain emergingcontaminants [47]. Its oxidative potential enables the degradation or transformation of different pollutant classes. Interestingly, nZVI can be generated in situ, allowing it to be directly applied to contaminated sites [48; 49; 50; 51]. This reduces the need for excavating and transporting contaminated soil or water, making it a cost-effective option in some scenarios. Finally, depending on the treatment process and conditions, nZVI particles can potentially be recovered and reused, reducing the overall cost and environmental impact of the treatment [52]. nZVI is typically produced through chemical or physical methods using iron precursors and a convenient reducing agent. In particular, green tea extract contains polyphenolic compounds with excellent reducing properties, meaning it can be used as an environmentally friendly reducing and stabilizing agent for nZVI [53; 54]. This improves its dispersion and stability in aqueous solutions, preventing the oxidation of nZVI and enhancing its reactivity and longevity. All these properties increase the effectiveness of nZVI generated with the aid of green tea extract in pollutant removal [55]. However, the successful application of nZVI in AOPs requires careful optimization of operational parameters, such as pH, temperature, contact time, and dosage [56; 57; 58]. In this work, zero-valent iron nanoparticles have been synthesized using green tea leaf extract as an alternative to conventional reducing agents. Next, nZVI generated in situ was used to remove two dyes, namely chrysoidine G and methylene blue, from an aqueous solution through Fenton-type advanced oxidation processes. The statistical design of experiments and Response Surface Methodology have been applied to analyze the influence of four parameters (namely the initial concentrations of Fe\({}^{2+}\), Fe\({}^{3+}\), H\({}_{2}\)O\({}_{2}\), and the reducing agent) on the efficiency of elimination of each dye.