Table 1

Description of chemical preparation methods of MNPs and their strength and weaknesses

Method	Procedure	Strength	Weakness	Reference
Co-precipitation	The precipitation of metal salts under alkaline conditions to produce MNPs at room temperature or elevated temperature	Facile, convenient Cost-effective Easy to implement Less hazardous reagents Large-scale preparation	Unstable Polydisperse	⁷¹
Thermal decomposition	The decomposition of organometallic compounds and oxidation in high boiling point organic solvents containing stabilizing surfactants	Highly monodisperse Controlled structure and performance	High temperature Complicated MNPs dissolved in non-polar solvents	⁷²
Hydrothermal	A phase transfer and separation process at the interfaces of the liquid, solid, and solution phases at high temperature (130–250 °C) and high pressure (0.3–4 MPa)	Simple Low cost Water dispersible Controlled morphology High purity and crystallinity	High temperature High pressure	⁷³
Microemulsion	MNPs are generated by mixing inorganic salt and precipitating agent contained in the oil/water or water/oil nanodroplets	Adequate Versatile Controlled size and shape	Low yield Complicated purifying procedure	⁷⁵
Sol-gel	Hydrolysis and polycondensation of metal precursors, metal, or metalloid element surrounded by various reactive ligands to form a “sol,” then dried by solvent removal or chemical reaction to form “gel,” followed by heat treatment for MNP harvesting	Pure Stoichiometric Monodisperse Large size Controlled structure	Low stability in aqueous solution	^76,77
Polyol synthesis	It is based on a transfer and separation mechanism occurring at the interfaces of the metal precursor (solid), organic solvent (liquid) and water solution containing polyol derivatives.	Simple, reproducible Monodisperse Controlled morphology Cost effective Good crystallinity Excellent magnetic property	High temperature High pressure Toxic organic solvents	⁷⁸

MNPs, magnetic nanoparticles.