Table 1.

Synthesis techniques, characterisation and applications of CuO NPs

S.no	Method	Technique	Chemicals	Characterisation	Results	Advantages	Disadvantages	Applications	References
1	physical	laser ablation	99.99% copper target, deionised water, d/f laser focusing conditions	ellipsoidal shaped NPs, monoclinic CuO and cubic Cu2 O 25–200 nm	laser ablation, pressure, temperature ultimately induced structural modifications in NPs	no capping, stabilising agents required	less concentration of NPs produced, high energy is required	nanolubricant, heterogeneous catalyst, sensors and so on	[12]

S.no	Method	Technique	Chemicals	Characterisation	Results	Advantages	Disadvantages	Applications	References
2	chemical	reduction method	copper (II) succinate as precursor	crystalline 45 nm average diameter	controlled particle size	simple, economical, efficient, surfactants prevents agglomeration of NPs, controlled size and shape of NPs	instability of NPs in solution	antimicrobial	[13]
		sol–gel method	sodium dodecyl sulphate as a surfactant	monoclinic, crystalline NPs	particle size increase with calcination b/c of agglomeration	controlled size and shape NPs	expensive and less eco‐friendly, costly	applications in gas sensing	[14]
		chemical vapour deposition	copper nitrate tri‐hydrate 0.02M, distilled water, 0.5 g sodium hydroxide at 5C	rod like structures, monoclinic 33 nm	widely dispersed	synthesis of controlled size and shaped NPs	needs high temperature	antimicrobial	[15]
		precipitation method	copper (II) acetate and sodium hydroxide	crystalline NPs 23 nm	reproducable procedure	simple and effective	inappropriate for the synthesis of pure, price stoichiometric phase	biocidal	[16]
		electro‐chemical deposition	supporting electrolytes, NaOH, NaCO3, sodium nitrate in water, water:acetonitrile (12:1), water:methanol (12:1), copper plate	well dispersed, granular spherical, round shaped, 20–25 nm, peaks at 2θ values	small sized particles	cost‐effective, less laborious, pure and controlled size and shaped NPs are synthesised	lack of reproducibility, needs high energy, pressure and temperature	photocatalytic and antibacterial	[14]
		hydrothermal	copper sulphate and NaOH	crystalline monoclinic, 27 nm average size	large optical band energy observed	variable NPs produced	high pressure and temperature is required	—	[17]
		ultrasonication synthesis of CuO/Cu2 O/Cu‐NPs	2.0 g copper acetate monohydrate, ammonia solution (25% w/w)	monoclinic crystalline,bandgap 1.42 eV, major peaks at 2θ values	simple but specific instrument required	effective, simple, cheap, non‐toxic	scale up problems	could be used as industrial catalysts for photocatalytic degradation of dyes	[18]

S.no	Method	Technique	Chemicals	Characterisation	Results	Advantages	Disadvantages	Applications	References
3	biological	E. coli mediated	citrate minimal medium, CuSO4, E. coli mass, SDS‐PAGE	micrometre dimensions and variable morphologies	use of SDS‐PAGE resulted in reduction of Cu II to CuO NPs and their stabilisation	high yield, low cost, fast. Clean, reproducibility	tedious purification steps, difficult to understand the mechanism and to achieve control size and shape of NPs	antimicrobial applications	[19]
		fungi mediated (Trichoderma asperellum)	5 mM copper nitrate, TA‐CFE (mycelial free water extract)	crystalline and cubic‐faced structure, 110 nm average size	ROS production and cellular observation in A549 cancer cells and the activity increased with TA‐CuO NPs	high yields secretory proteins related to increase NPs, scalability, easy downstream processing	risk of pathogenicity	TA‐CuO NPs could be used as therapeutics in modern medicines	[20, 21]
		plant mediated Hibiscus rosa‐sinensis (flower extracts)	1 M aqueous copper acetate solution, deionised water	crystalline, spherical, 45–80 nm	antimicrobial	cost‐ effective, eco‐friendly, easy availability, high quality NPs, controlled size and shape	difficulty and time consuming	antimicrobial applications	[22]
		algae mediated (Bifurcaria bifurcate)	1 mM copper(II) sulphate, 2 ml algal extract	crystalline NPs, 5–45 nm average size	antimicrobial	eco‐friendly, convenient, no chemicals involved	laborious and slow process	pharmaceutical	[23]