TABLE 1.

Different synthesis methods of MNPs with respective merits and demerits.

Synthesis methods	Merits	Demerits	References
Ball milling method	Simple, widely used, produce fine powder	Contamination of product	Benjamin (1970), Sarwat (2017)
Laser evaporation	Low experimental cost, no use of chemicals, no pollutant products	High price of laser system, needs high amount of energy	Yang (2007), Jendrzej et al. (2017)
Wire explosion method	Ecologically safe, clean, and highly productive	A little contamination of product may occur	Kotov, (2003)
Coprecipitation	Simple, large quantity	Impurities, time consuming	Jiang et al. (2004)
Thermal decomposition	Controllable size, high yield	Toxic solvents	Faraji et al. (2010)
Microemulsion synthesis	Thermodynamically stable	Low yield	Vidal-Vidal et al. (2006)
Hydrothermal/Solvothermal	Good crystallinity	Needs high temp. and pressure	Wu et al. (2008)
Sol-gel method	Highly pure, good crystallinity	Longer time, toxic organic solvents	Duan et al. (2018)
Sonochemical reaction	High crystallinity, saturation magnetization, narrow size distribution	Mechanism is still not well understood	Unsoy et al. (2012)
Microwave	Fast, rapid kinetic for crystallization	Homogenous nucleation due to uniform heating	Namboodiri and Varma, (2001)
Chemical reduction	Simplicity, safe	Environmental pollution	Sun et al. (2007)
Chemical vapor deposition	Wide range production of materials	Low productivity, impurities	Wang et al. (2003)
Arc discharge	Simple, low cost	Difficult to control particle size	Faraji et al. (2010)
Laser pyrolysis	Highly localized heating and rapid cooling	Expensive	Hasany et al. (2012)
Combustion synthesis	Simple, fast, low cast	Generate impurities	Borysiuk et al. (2008)
Annealing	Controllable particle size and chemical composition	Generate impurities	Wang et al. (2007)
Biological method	Efficient, clean process, ecofriendly	Poor dispersion of NPs	Komeili, (2012)