Table 2.

Techniques for the synthesis of ZnO NPs.

Synthesis Technique		Advantages	Disadvantages	References
Physical methods	-Arc plasma -Thermal evaporation -Physical vapor deposition -Ultrasonic irradiation -Laser ablation	▪Simple ▪Low cost ▪Catalyst-free ▪Industrial-scale production	▪Parameter control	[9,54,55,56,57,58,59,60,61,62,63,64,65,66,67]
Chemical methods	-Microemulsion -Sol–gel -Precipitation -Hydrothermal method -Solvothermal method -Chemical vapor deposition	▪Inexpensive and easy-to-handle chemical reagents ▪Uncomplicated equipment ▪Low energy input ▪Easy parameter tailoring ▪Industrial-scale production	▪Surfactant use ▪High cost of precursors	[9,35,55,68,69,70,71,72,73,74,75,76]
Biological methods (green synthesis)	-Plant extracts -Microorganisms -Biotechnology method -Biochemistry method	▪Promising alternatives to chemical methods ▪Eco-friendly ▪Non-toxic (safer) ▪Inexpensive organic solvents	▪Nanoparticle stability ▪Antimicrobial activity ▪Unclear mechanism	[9,52,56,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97]
Microfluidic reactor-based methods	-Continuous flow -Segmented flow -Co-flow	▪High value-added products ▪Reproducible ▪Non-toxic	▪Parameter control	[98,99,100,101,102,103,104,105,106,107]