## 5 Novel Magnetic Ferrite Nanoparticle Applications in Wastewater Treatment
### Magnetic Ferrite Nanoparticles for Photocatalytic Degradation of Wastewater Pollutants
The type of photodegradation is a Fenton-type photocatalyst system, including oxidizing agents in the form of peroxides, which improves the degradation efficiency of CuFe\({}_{2}\)O\({}_{4}\) nanoparticles. While Fe\({}^{3+}\) reacts with H\({}_{2}\)O\({}_{2}\) to form HOO\({}^{\bullet}\) radicals, these peroxides will react with Fe\({}^{2+}\) to produce more reactive hydroxyl radicals. As a result, the concentration of reactive species increases, eventually increasing the degradation of the dye. Due to high-energy photons, UV energy also boosts the electron-hole pair generation and, eventually, degradation efficiency [247]. These characteristics have led CuFe\({}_{2}\)O\({}_{4}\) NPs to be applied in photocatalytic reactions specifically for wastewater treatment applications. [PERSON] et al. synthesized a ZnO/ZnFe\({}_{2}\)O\({}_{4}\) heterojunction photocatalyst via a solvothermal process and achieved superior crystalline and optical properties, and proved that a ZnO/ZnFe\({}_{2}\)O\({}_{4}\) composite shows enhanced photocatalytic activity as compared to individual ZnO and ZnFe\({}_{2}\)O\({}_{4}\) nanoparticles for the degradation of methylene blue, achieving 91.2% and 82.7% degradation efficiency after 120 min of UV-vis (\(350\leq\lambda\leq 780\) nm) and 140 min of visible light (\(\lambda\geq 420\) nm) irradiation, respectively [242]. Similarly, [PERSON] et al. synthesized ZnCuFe\({}_{2}\)O\({}_{4}\) nanoparticles via the coprecipitation method and studied various operational parameters on the performance of ZnCu-based magnetic ferrite nanoparticles, e.g., pollutant concentration, pH levels, nanoparticles' dosage, and photocatalytic activity. The photocatalytic activity was observed under UV light for the degradation of methylene blue azo dye and 94% efficiency was observed after 135 min of exposure at room temperature and a pH of 9 [238]. In an investigation, [PERSON] et al. synthesized CoNiFe\({}_{2}\)O\({}_{4}\) magnetic ferrite nanostructures via the coprecipitation method and studied pre-annealed samples for the photodegradation of Congo red dye, which is the major textile industry waste. They illuminated Congo red dye containing water in continuous solar illumination for 90 min and proved that CoNiFe\({}_{2}\)O\({}_{4}\) magnetic ferrite nanoparticles pre-annealed at 750 \({}^{\circ}\)C show a maximum efficiency of 94.8% and that they can be used many times [247]. In another contribution, [PERSON] et al. synthesized Nd-doped NiFe\({}_{2}\)O\({}_{4}\) nanocomposites with carbon nanotubes via the coprecipitation method and showed that Nd-doped composites with carbon nanotubes show much better photodegradation performance as compared to pristine NiFe\({}_{2}\)O\({}_{4}\) nanoparticles. They studied the photodegradation performance of three major textile wastes, Rhodamine B, methylene blue, and benzoic acid, for 90 min under visible light illumination, where Nd-doped NiFe\({}_{2}\)O\({}_{4}\) shows the highest efficiencies of 83.87%, 90.80%, and 66.96% for Rhodamine B, methylene blue, and benzoic acid, respectively. It was concluded that the reason for the superior activity of Nd-doped NiFe\({}_{2}\)O\({}_{4}\) is due to the existence of rare earth Nd ions and carbon nanotubes [248]. The removal of complex organic molecules, e.g., dyes, pharmaceuticals, and pesticides, needs more complex and advanced wastewater treatment strategies as compared to conventional water treatment strategies. Scientists have widely studied such complex organic compound removal. Industry, agricultural activities,and domestic wastewater are major sources of complex organic compounds. The usage of a conventional wastewater treatment from dyes exhibits numerous challenges, e.g., greater stability to degradation due to the presence of aromatic rings [249]. Their degradation pathway can be readily followed by UV-vis spectroscopy and modeled using kinetic models like that of Langmuir-Hinshelwood; these colored dyes are typically researched as model reactions for the breakdown of big organic molecules [121].