The FTIR stretching of different functional groups formed during synthesis of NPs and fresh lemon juice.

Name of materials	Functional groups	Frequency (cm−1)	References
CuONPs	Cu–O	620	31,39,61,64,65
	O–H	3360
	C O	1657
	C–O	1046
	C–H	2071
Lemon juice (citric acid)	O–H	3290	67,68
	C O	1712
	C–OH	1105
	CH2	778