3.1. X-Ray Diffraction (XRD) analysis
XRD is the most effective and famous technique to measure crystal structure and crystalline size, which means it can give comprehensive information about crystal structure. The crystalline nature of the Cu NPs has been confirmed as the biosynthesized technique by XRD and the representative XRD patterns, which are shown in Fig. 2 (a). The diffraction peaks were obtained at the 2θ values corresponding to the planes (110), (111), and (200), which were 36.380, 43.360, and 50.350 respectively. This XRD result suggests that the prepared Cu NPs are face-centered cubic [26]. The average crystallite size of the prepared samples was determined from the most substantial peak using Scherrer’s formula, and the calculated crystallite size was about 19 nm.
XRD confirmed Ag NPs and Cu-Ag NPs as crystalline in the biosynthesized technique, and the representative patterns are shown in Fig. 2 (b). The diffraction peaks (Ag NPs) were obtained at the 2θ values corresponding to the plane (110), (111), (200), and (220) were 38.200, 44.450, and 64.410, respectively. This result also recommends that the prepared Ag NPs be face-centered cubic [27]. Moreover. The average crystallite size was calculated from the most substantial peak using Scherrer’s formula, and the considered crystallite size was about 13 nm. Similarly, (Cu-Ag NPS) 2θ values corresponding to the planes (110), (111), (200), and (220) are 38.190, 44.42, and 64.610, respectively. Compared with the standard curve, our prepared Cu-Ag NPs are face-centered cubic in nature [28]. Here we see that Ag is the dominating part of Cu-Ag nanoparticles, and the XRD peaks are associated with silver nanoparticles, which are found in Fig. 2 (b). The average crystallite size of the prepared samples was determined from the most substantial peak, and the calculated crystallite size was about 23.15 nm. In the above three XRD patterns, some unsigned peaks may be associated with the organic compounds that originate from the banana leaf extract and act as capping agents. These unsigned peaks also support the FTIR data, where we found many organic compounds.
3.2. Energy Dispersive X-ray (EDS) spectroscopy analysis
Elemental analysis of the synthesized bio-organic components coming from Musa paradisiaca leaf extract was performed using EDS spectra analysis and is shown in Fig. 3. (a) Cu NPs, (b) Ag NPs, and (c) Cu-Ag NPs. This is very clear in Fig. 3. (a), The EDS profile has shown strong signals for silver atoms. The strong signal peak at 7.8 keV in the EDS spectrum was typical of the absorption of silver nanocrystallites [29], and the weak signals are found at 1 keV, 8.5 keV, and 9.0 keV, which establishes the presence of Ag NPs.
In Fig. 3. (b), the EDS profile showed solid signals for copper atoms. The strong signal peak at 0.9 keV in the EDS spectrum was typical of the absorption of copper nanocrystallites, and the weak signal peak at 8 keV and 9 keV was also found.
Further investigation of bimetallic nanoparticles, the EDS profile Fig. 3. (c) provided strong signals for copper and silver atoms. The strong signal peak at 0.9 keV in the EDS spectrum was distinctive from the absorption of copper nanocrystals. The weak signals were in 0.3 keV, 0.7 keV, 8.0 keV, and 9.0 keV strongly exhibited the presence of copper nanoparticles [30]. The strong signal peak at 3.0 keV in the EDS spectrum was typical of the absorption of silver nanocrystallites, and the weak signals at 3.2 keV and 3.5 keV strongly showed the presence of silver nanoparticles [31]. So, this showed the presence of Cu-Ag NPs.
In the above three EDS spectra, some other elements, interestingly details features such as C, N, and O, were also detected. C, N, Cl, and O are likely associated with the organic compounds from the banana leaf extract absorbed on the surface of Cu NPs, Ag NPs, and Cu-Ag NPs, which play a crucial role in the reduction and stability. Even if we carefully observe the XRD pattern’s unsigned peak, which supports these extra elements in the EDS signal, most of which are organic compounds. Moreover, this organic compound is mainly responsible for reducing and stabilizing the nanoparticles [30–31].
3.3. Field Emission Scanning Electron Microscopy (FESEM) analysis
The surface morphology of the synthesized nanoparticles was monitored using Field Emission Scanning Electron Microscopy (FESEM) technique and shown in Fig. 4. The FESEM image of 4 (a) Cu NPs, (b) Ag NPs, and (c) Cu-Ag NPs clearly showed that the green synthesized nanoparticles were uniformly distributed with lowering agglomeration. The gross calculation can be drawn from the image of part of the size range. It was evident in the SEM image that all of the particles were in the nao scale range. We used the popular software named “ImageJ” for more accurate calculation. After analyzing the result, the particle size range for (a) Cu NPs, was found (5nm − 35 nm). Maximum particle distribution belongs to (12 nm-18 nm), and the average particle size is about (17 nm), which is enough for nanoparticle confirmation. In Fig. 4 (b) for Ag NPs, most of the particles were in a nanoscale range which can define as (10 nm – 60 nm). Most of the particle Particles were distributed from 15 nm to 30 nm. The number of particles in the lower and upper range was not huge. The average particle size was calculated at about 24 nm, slightly greater than Cu NPs. Cu-Ag bimetallic nanoparticles’ size value started from 20 nm, and the maximum range of particles was about 90. In the region, 40 nm -50 nm ultimate particles were obtained, and the average size of the whole particles was 48 nm. The average size is slightly larger than previous Cu NPs and Ag NP’s average size. At the calculation time, few particles in the above three types were larger than intermediate particles. The large particles were probably due to the accumulation of small ones [32]. The large particle may be reduced by heat treatment. Identical results were also found in different experiments where agglomeration is mainly responsible for obtaining large particles [33]. The lowering of the aggregation might be due to the presence of capping agents on the surface of Ag NPs, Cu NPs, and Cu-Ag NPs, which was also evidenced by the EDX and FT-IR analyses.
3.4. Fourier Transform Infrared (FT-IR) spectra analysis
Cu NPs (a) are shown in Fig. 5, and the resulting peaks correspond to the following frequencies: 482.20 cm− 1, 1099.43 cm− 1, 1365.60 cm− 1, 1624.06 cm− 1, 3435.22 cm-1, and 3772.76 cm− 1. Table 1 contains a tabulation of those peaks arranged according to the functional category they belong to. Numerous additional bioorganic compounds can exist in the solution and contribute to reducing copper ions and stabilizing the nanoparticles generated due to surface capping. At this time, we were working on isolating the various bioorganic fractions in the banana leaf broth so that we may examine each one separately for its ability to inhibit copper ion reduction and to bond with nanoparticles.
Table 1
Summary of (FT-IR) spectra analysis of Banana leaf, Banana leaf extract mediated (a) Cu NPs, (b) Ag NPs, (c) Cu-Ag NPs, and (d) Musa paradisiaca leaf (Banana leaf) powder
Spectrum number and name
|
Wave number
|
Functional group
|
Reference
|
(a) Cu NPs
|
i).482.20cm-1
ii).1099.43cm-1
iii). 1365.60cm-1
iv). 1624.06cm-1
v). 3435.22 cm-1
vi). 3772.76 cm-1
|
i). (Alkyl Halide)
ii). (Alcohol) or C-N (Amine)
iii). C-H for (Alkane) or C-F (Alkyl Halide)
iv). C=C(Alkene)
v). O-H (Alcohol)
vi). N-H (Amine)
|
[34]
|
(b) Ag NPs
|
i) 470.63cm-1
ii) 1083.99cm-1
iii) 1355.96cm-1
iv) 1602.85cm-1
v) 3435.22cm-1
|
i) (Alkyl Halide)
ii)(Alcohol)/C-N (Amine)
iii) C-H for (Alkane) or C-F (Alkyl Halide)
iv) C=C(Alkene)
v) (Alcohol) or N-H (Amine)
|
[35]
|
(c) Cu-Ag NPs
|
i) 478.35cm-1
ii) 1060.85cm-1
iii) 1379.10cm-1
iv) 1622.13cm-1
v)3437.15, 3693.68, 3770.84 cm-1
|
i) (Alkyl Halide)
ii)(Alcohol)/C-N (Amine)
iii) C-H for (Alkane) or C-F (Alkyl Halide)
iv) C=C(Alkene)
v) (Alcohol) or N-H (Amine)
|
[36,37]
|
(d) Musa paradisiaca leaf (Banana leaf) powder
|
i) 518.85cm-1
ii) 653.87cm-1
iii) 1066.64 cm-1
iv)1321.24cm-1, 1384.89cm-1
v) 1629.85cm-1
vi) 2860.43cm-1, and 2922.16cm-1
vii) 3429.43cm-1
viii) 3711.04 cm-1, and 3770.84 cm-1
|
i) (Alkyl Halide)
ii)C-Cl (Alkyl chloride),
iii) O-H (Alcohol) or C-F (Alkyl fluoride), iv) different types of amine group (N-H),
v) C=C (Alkene) or C=O (Carbonyl),
vi) alkanes C-H
vii) N-H (Amine)
viii) O-H (Alcohol)
|
[37]
|
In Fig. 5, the locations of the peaks at 470.63 cm− 1, 1083.99 cm− 1, 1355.96 cm− 1, 1602.85 cm− 1, and 3435.22 cm− 1 were revealed in the curve "b" which was the FTIR spectrum of the produced Ag NPs. It was compared to common values, and a few organic groups were also discovered for the location of the peaks above it. In the end, each and every one of them was included in Table 1. Terpenoids were also responsible for the reduction of silver ions. During this process, the terpenoids were oxidized to carbonyl groups, which led to the formation of a band at 1602.85 cm− 1. The peak corresponding to the amine band at 1083.99cm− 1 has enlarged due to the creation of Ag NPs, which shows that the protein is responsible for capping the silver nanoparticles [34]. It is well known that proteins may attach to silver nanoparticles (Ag NPs) through free amine group residues [35]. It has been shown that plants exude many secondary metabolites that encompass a wide variety of organic structures. A variety of additional bioorganic substances were capable of being in the solution and taking part in lowering the number of silver ions while simultaneously stabilizing the nanoparticles.
Represented the leaf extract mediated (curve “c”) Cu-Ag NPs, and the peaks that were produced corresponded to the following wavelengths: 478.35cm− 1 for (Alkyl Halide), 1060.85cm− 1 for (Alcohol) or C-N (Amine), 1379.10cm− 1 for C-H for (Alkane) or C-F (Alkyl Halide), 1622.13cm The peak that corresponds to the amine band at 1060.85cm− 1 has expanded during the creation of Ag NPs, which shows that the protein is responsible for capping the copper and silver nanoparticles [36]. It is also well knowledge that proteins include free amine group residues that, when exposed to Cu-Ag NPs, may cause a binding reaction [37].
An FT-IR spectrometer recorded the spectra of Fourier Transform Infrared (FT-IR) on a dried sample of Musa paradisiaca (Banana) in the area of wavenumber ranging from 4000 to 400 cm− 1 vs. transmittance varying from 60–100 percent. These results are shown in Fig. 5. (curve “d”). The corresponding organic functional groups for peak values were maybe 518.85 cm− 1 for C-X (alkyl halide), 653.87 cm− 1 for C-Cl (Alkyl chloride), 1066.64 cm− 1 for O-H (alcohol) or C-F (alkyl fluoride), 1321.24 cm− 1, 1384.89 cm− 1 for various types of an amine group (N-H), and 1629.85 cm− 1 for The simple Musa paradisiaca leaf, sometimes known as the banana leaf, had no harmful functional groups in any of its constituent components. The results of the four spectra were summarized in Table 1.
The leaf extract solution was most likely the origin of the bioorganic component that was used in the synthesis of copper nanoparticles, silver nanoparticles, and copper-silver nanoparticles (Cu-Ag NPs). Therefore, it is possible to hypothesize that numerous bioorganic composites are present in the solution and contribute to the reduction of copper and silver ions and the stability of the nanoparticles generated as a result of surface capping. The Musa paradisiaca leaf, sometimes known as banana leaf, served as the basis for this non-hazardous and effective pesticide alternative.
3.5. Thermo Gravimetric Analysis (TGA)
To examine the thermal stability of (a) Cu NPs, (b) Cu-Ag NPs, and (c) Ag NPs in (Fig. 6), Thermo Gravimetric Analysis (TGA) was carried out between 240C and 800°C and the corresponding data was shown in Fig. 6. The weight loss in the first 13.23 min was observed up to 166.08°C (4.03%) (Fig,6, curve a), which may be attributed to the release of water molecules adsorbed on the surface of Cu NPs. The weight loss for 54.41 min was obtained up to 577.38°C (36.10%), which might be due to the release of organic compounds attached to the surface of Cu NPs acting as capping agents.
To study the thermal stability of bimetallic Cu-Ag NPs, Thermo Gravimetric Analysis (TGA) was carried out. The weight loss in the first 15.80 min was observed up to 181.44°C (4.6%) (Fig. 6, curve b), which may be associated with the release of water molecules on the surface Cu-Ag NPs. The weight loss in a time of 57.54 min was detected at 600.98°C (25.32%) mainly occurred to releasing organic compounds attached to the surface of Cu-Ag NPs. The weight loss by increasing temperature is less than Cu and Ag nanoparticles.
Similarly, in the case of Ag NPs, the weight loss in the first 19.32 min was observed up to 220.09°C (6.77%) (Fig. 6, curve c) for releasing water molecules from the surface of Ag NPs. The weight loss in 54.33 min was found up to 570.64°C (38.99%), which might be due to the release of attached organic compounds on the surface of Ag NPs acting as capping stabilizing agents. Similar studies were reported by earlier workers [38]. The EDS and FT-IR analyses also evidenced the presence of capping and stabilizing agents.
3.6. Magnetic property analysis
The magnetic property of synthesized Cu-Ag NPs was examined using Vibrating Sample Magnetometer (VSM) analysis, and the corresponding hysteresis loop was shown in Fig. 7. The hysteresis loops of the VSM analysis showed that the synthesized Cu-Ag NPs showed a ferromagnetic nature at room temperature. The saturation magnetization (Ms) was calculated as 0.58 emu g− 1, and the coercivity (Hc) was 153 Oe.
It is common knowledge that the size of nanomaterials plays a significant part in determining their electrical, chemical, optical, and magnetic characteristics. The discovery that nanoparticles of materials like metal oxides and other inorganic materials may exhibit ferromagnetism, even though the bulk state of these substances is diamagnetic [39]. The charge transfer generated by the 5d localized holes in this nanoparticle gives it its ferromagnetic property [40]. Since the charge is being transferred, the formation of orbital magnetism from spin-orbit couplings has been a topic of discussion [41]. Researchers believe that the ferromagnetic character of surface Nobel atoms, caused by the Fermi hole effect, is responsible for the dependency of ferromagnetism on particle size. An X-ray circular dichroism investigation concluded that nanoparticle spin polarization is due to localized holes [41]. According to a number of the findings, it would seem that the presence of thiol or amine capping agents is required for the magnetism of nanoparticles. The ferromagnetic behavior of our green synthesized Cu-Ag NPs could be said to be due to the Nano-sized dimension and the presence of amine or thiol groups on the surface of Cu-Ag NPs, which also agreed well with the EDX and FT-IR analyses. In our earlier studies, we demonstrated that produced silver nanoparticles had magnetic properties [24]. According to the findings of this work, it was also weakly ferromagnetic in bimetallic forms such as Cu-Ag nanoparticles. In addition, most of the bimetallic that we synthesized consisted of silver.