Table 1.

Overview of some synthesis methods for nZnO.

Method	Used Precursors	Conditions	Structure; Size	References
Ultrasonics	Zn(NO3)2·6H2O, C6H8O7·H2O	Sonication for 0.5–2 h, room temperature	Hexagonal, spherical particles	[71]
Chemical bath deposition (CBD)	Zn(CH3CO2)2·2H2O, C2H4(NH2)2	80 °C temperature, magnetic stirring up to 3 h	Core shell rod like structure, size 500 nm	[72]
Sol-gel	Zn(CH3CO2)2, C2H5OH, (C6H9NO)n	100 °C temperature, stirring time 2 h, calcination at 300 °C	Size 140 nm	[73]
Sol-gel	Zn(CH3CO2)2·2H2O, C2H5OH, NaOH	60 °C temperature, time 17 h, annealing at 200 °C	Hexagonal wurtzite, spherical, size 22 nm	[74]
Co-precipitation	Zn(CH3CO2)2·2H2O, NaOH, C2H5OH, NH4OH	Agitation time 1 h, annealing at 60 °C, for 6 h	Nanorods, wurtzite crystal structure	[75]
Successive ionic layer adsorption and reaction (SILAR)	ZnSO4⋅7H2O, NH4OH, CuSO4·5H2O	Dipping cycles 30, annealing 500 °C for 2 h	Hexagonal wurtzite, spherical, size 34 nm	[76]
Hydrothermal	Zn(NO3)2·6H2O, NaOH, Zn(CH3CO2)2·2H2O, C2H5OH,	Heating 50 °C, stirring 30 min, oven drying 150 °C for 6 h	Nanorods, wurtzite crystal structure	[77]
Two step sonication modified sol-gel	Zn(CH3CO2)2·2H2O, NH4OH, KOH, Tetraethyl orthosilicate (TEOS)	60 °C temperature, time 1.5 h, sonication time 1 h	Hexagonal wurtzite, spherical nanoparticles	[78]
Biological	Tabernaemontana divaricata leaves extract, Zn(NO3)2·6H2O	80 °C temperature, continuous stirring, drying at 450 °C for 2 h	Hexagonal wurtzite, spherical, size 20–50 nm	[79]
	Abutilon indicum leaves extract, Zn(NO3)2·6H2O	Temperature of furnace at 200 °C for 3 min., calcination for 2 h	Hexagonal wurtzite, spheroid rod like shape, size 16–20 nm, band gap 3.36 eV.	[80]