## 4 Chemical Methods for Synthesis of Magnetic Ferrite Nanoparticles
### Sol-Gel Method  
Magnetic ferrite nanoparticles synthesized via the sol-gel method offer remarkable versatility and control over their properties. The sol-gel method involves creating a colloidal solution that transitions into a gel-like network, allowing precise manipulation of parameters such as pH, typically regulated between 2 and 12, depending on the metal salts and specific requirements. Hydrolysis and condensation reactions are usually conducted at room temperature, while calcination is performed at higher temperatures ranging from 400 \({}^{\circ}\)C to 800 \({}^{\circ}\)C to crystallize the material. Typical gelling agents such as citric acid, tartaric acid, and various organic solvents facilitate gel formation. This approach enables the production of magnetic ferrite nanoparticles with tailored properties for a wide range of applications [171; 172; 173]. The sol-gel method entails preparing a sol in which metal salts (e.g., nitrates, chlorides, acetates) are dissolved in a solvent and then undergo hydrolysis and condensation reactions to form a colloidal suspension, thereby transitioning metal precursors from a sol to a gel state [174]. This sol transitions into a gel-like network through additional polymerization. The gel is then aged to stabilize its structure, followed by drying to eliminate the solvent, resulting in a porous xerogel. Lastly, the xerogel is calcined at high temperatures to remove organic residues and crystallize the material (Figure 7) [175; 176; 177; 172]. Simple spinel ferrites such as CuFe\({}_{2}\)O\({}_{4}\), ZnFe\({}_{2}\)O\({}_{4}\), NiFe\({}_{2}\)O\({}_{4}\), and CdFe\({}_{2}\)O\({}_{4}\) were synthesized via the sol-gel method. The pH was maintained between 7 and 8, and the sol was heated to 80 \({}^{\circ}\)C. At 250 \({}^{\circ}\)C, the dry gel ignited, producing a loose ferrite nanopowder through self-propagating combustion, which was then annealed at 500 \({}^{\circ}\)C for 5 h [178]. Figure 7: \(Cont.\)  
The key parameters affecting the crystallite size of magnetic ferrite nanoparticles in sol-gel synthesis include the synthesis parameters and conditions. Precursor materials can significantly influence the crystallite size of magnetic ferrite nanoparticles. Different precursor materials can affect the rate of hydrolysis and condensation reactions, which in turn impacts the nucleation and growth of nanoparticles. For instance, [PERSON] et al. synthesized cobalt ferrite nanoparticles using sago starch as a chelating agent. They discovered that the particle sizes ranged from 30 to 500 nm, which depended on the weight ratio of metal nitrates to sago starch--specifically, variations in the ratio from 1:8 to 1:12 produced particles within this size range. However, increasing the sago starch ratio to 1:16 resulted in ferrimagnetic hysteresis loops with a reduced coercive field and magnetization due to the formation of a second phase, hematite (\(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)) [180]. [PERSON] et al. developed a honey-mediated, self-sustaining sol-gel combustion technique to synthesize CoFe\({}_{2}\)O\({}_{4}\) nanoparticles with controlled size and shape. These nanoparticles were annealed at temperatures of 500 \({}^{\circ}\)C, 700 \({}^{\circ}\)C, 900 \({}^{\circ}\)C, and 1100 \({}^{\circ}\)C to enhance their properties. This method showcases the effectiveness of using natural chelating agents like honey in advanced magnetic material synthesis [181]. The size of magnetic ferrite nanoparticles critically influences their magnetic characteristics in sol-gel synthesis methods. This allows for exact control over the particle composition and structure, facilitating the creation of highly uniform nanoparticles with tailor-made magnetic properties. These properties are especially beneficial for the adsorption of pollutants and magnetic separation [182; 183; 184; 185; 186; 187; 188; 189; 190; 191; 192; 193; 194; 195; 196;  
netic ferrite nanoparticles is its capacity to yield a greater quantity of samples in a reduced timeframe [188].