Table 1.

A summary of various methods for the synthesis of nanomaterials.

Nanomaterials synthetis method	Mechanisms involved	Advantages and Disadvantages	Ref.
Mechanical milling	Impact of the ball-powder-ball collision on powder particles which undergo deformations and/or fractures, thus achieving size reduction and/or alloying	More economical for large scale processes; irregular particle shape and crystal defects are induced, creating a metastable composition	[34]
Lithography	Transfer of nanopatterns with templates for masked lithography and direct transfer for maskless approach. Another approach (nanosphere lithography) is through the dispersion of spherical colloids to form a colloidal crystal mask for selective patterning and allow deposition of desired materials	Can be top-down or bottom-up, generally high resolution of shape and position of NPs, yet production cost is high with low throughput	[36], [58], [59]
Laser-ablation	Removal of the surface atom from a solid target with a laser energy source. Nucleation of evaporated species and subsequent growth into NPs	A green method for controlled and high purity NP synthesis without using toxic chemicals, yet low production rates	[39]
Chemical etching	Chiseling of nanostructures out of solid surfaces through the use of etchants such as strong acids and/or alkalis	High etching rate and low equipment cost; difficulty in achieving smaller features and reliance on hazardous materials	[40], [60]
Sol-gel	Chemical method involving hydrolysis of precursors, polycondensation of molecules to form a network of colloids and subsequent aging, drying and calcination that controls the size and morphology of NPs	High control over NPs texture, achievable at a lower temperature; however, the processing time is long	[44]
Chemical vapour deposition	Vaccum deposition of vaporised precursors on heated substrates forming 2D NPs	High purity and homogeneity of the product. The process is limited by extremely high-temperature demand, and by-products are toxic gases	[46]
Biosynthesis	Use of microorganisms as bioagents, the enzymatic activities foster reduction and stabilization of NPs	Green and environmentally friendly approach, yet poor control over NPs size and many other mechanisms are still poorly understood	[49]
Pyrolysis	Thermal decomposition of precursors and subsequent formation and growth of particles by gas-phase chemical reactions and coagulation	High product yield and cost-effective but extreme synthesis conditions	[35]