5.1 Ultraviolet Visible Spectrophotometer:
The copper nanoparticles formation is usually confirmed by UV-Vis spectroscopy studies of colored solution [18]. The concept of obtaining the peak in the UV-Vis spectrum is that, on the surface of metal nanoparticles the free electrons will be present which undergoes strong repulsion with the light of specific wavelength [19]. Higher the conversion of copper sulphate solution to copper nanoparticles, higher will be the absorbance which corresponds to higher concentration of copper nanoparticles [20]. The spectroscopy studies of the solution were recorded after 24 hours. The peak of absorbance from the absorption spectra was between the ranges of 230 nm - 270 nm as shown in Fig. 3 pinpointing copper nanoparticles formation.
5.2 X-Ray Diffraction (XRD):
X-Ray Diffraction is an analytical method for determining the size and crystalline structure of the nanoparticles [21]. The high degree of crystallinity of nanoparticles is reflected by the intensity and sharpness of peaks [22]. There is an undeniable role played by the secondary metabolites in the plant extract even if the clear mechanism is unknown [23]. The average size of the copper nanoparticles was obtained using Scherrer's Formula,
Where Dp depicts the average grain size, K is Scherrer's constant which is 1.54060, λ denotes the X-Ray diffraction wavelength which has a value of 1.54178 nm, B is FWHM i.e, Full Width at Half Maximum derived from the peak of XRD. The observed XRD peak broadening is said to come from the crystalline size. θ is the XRD peak position (i.e.,) the Bragg's angle obtained from the half of 2θ, where 2θ is in the range of 30 – 80o [24].
Table 1
Peak (2θ)
|
θ
|
Sin2θ
|
sin2θ/
sin2θmin
|
3*
sin2θ/sinθmin
|
h2+k2+l2
|
hkl
|
a(Å)
|
FWHM
(°2Th)
|
d-spacing
(Å)
|
Dp
(nm)
|
34.96
|
17.48
|
0.0902
|
1
|
3
|
3
|
111
|
4.4407
|
0.5077
|
16.5184
|
17.15
|
41.50
|
20.75
|
0.1255
|
1.3914
|
4.1742
|
4
|
200
|
4.3471
|
0.5077
|
7.7959
|
17.50
|
58.37
|
29.185
|
0.2377
|
2.6364
|
7.9092
|
8
|
220
|
4.4671
|
0.3385
|
5.9188
|
28.11
|
69.34
|
34.67
|
0.3236
|
3.5876
|
10.7628
|
11
|
311
|
4.4893
|
0.4231
|
2.1759
|
23.87
|
75.57
|
37.785
|
0.3754
|
4.1619
|
12.4857
|
12
|
222
|
4.3535
|
0.5077
|
1.6591
|
20.70
|
|
|
|
|
|
|
|
Average a: 4.4195 Å
|
|
|
Average Dp: 21.47
nm
|
The average grain size of the copper nanoparticles was estimated as 21.47 nm. From the XRD curves, the intense and sharp peaks of the copper nanoparticles were observed at 34.96o, 41.50o, 58.37o, 69.34o, and 75.57o. It has the plane values as (111), (200), (220), (311), and (222) respectively. Therefore, all the diffraction peaks can be defined and indexed using face-centered cubic cell. The average lattice parameter value is determined to be 4.4195 Å. The XRD pattern proves the crystalline nature of the copper nanoparticles as shown in Fig 4. The obtained results illustrate that CuSO4 has indeed been reduced to Copper nanoparticles by Plectranthus amboinicus plant extract under the appropriate reaction medium and conditions.
5.3 Zeta Potential:
The Z-average was estimated as 5.3 nm as shown in the Fig 5(a) using DLS. The charge obtained using zeta analysis was -25.2mV as shown in the Fig 5(b). Particles that have charges of or above -25 and +25 tend to be more stable according to the previous research documents [25]. Particles that have negative charges tend to have a strong force of repulsion between them. This indicates the properties of stability and quality [26].