## 3 Results and Discussion  
### Characterization of the Adsorbent  
Figure 3 presents the functional groups in the AgNPs before and after the adsorption of Cu\({}^{2+}\). It was noted that the peaks at 3423, 2925, 1623, 1384, 1321, 1073, 766, 606, and 514 cm\({}^{-1}\) were referred to the functional groups in the AgNPs synthesized using the _C. arvensis_ leaf extract. The stretching of the functional groups in the AgNPs were associated with the peaks at 3408, 2918, 1624, 1324, 1000, 782,  
Figure 2: The synthesis of AgNPs.  
and 538 cm\({}^{-1}\) arising after the Cu\({}^{2+}\) adsorption. It was observed that the peaks at 3423 and 3408 cm\({}^{-1}\) in the AgNPs spectra before and after the Cu\({}^{2+}\) adsorption, respectively, appeared as a result of the stretching of the N-H or O-H groups. The secondary peaks at 2925 and 2918 cm\({}^{-1}\) were caused by the stretching of the C-H groups. The band regions at 1623 and 1624 cm\({}^{-1}\) were related to the presence of C=O bonds. In addition, after the adsorption of Cu\({}^{2+}\) ions, the two absorption peaks that appeared at 1384 and 1321 cm\({}^{-1}\) in the AgNPs spectrum agreed to the groups of N=O and N-O, respectively, whereas the peak at 1324 cm\({}^{-1}\) was ascribed to the N-O band of the AgNPs [3; 4; 8; 21]. The peaks at 1073 and 1000 cm\({}^{-1}\) were due to the N-H, C-N, or C-O groups extending, and the peaks at 766, 782, and 514-538 cm\({}^{-1}\) were due to the stretching of the H\({}_{3}\)CO and C-H groups [14; 22].  
The above results demonstrate that the presence of the functional groups, including carboxyl, facilitate the adsorption process of Cu\({}^{2+}\) via ion exchange. Moreover, the presence of the hydroxyl groups in the adsorbent allows the coordination bonds to form with the Cu\({}^{2+}\) ions.  
EDS was used to analyze the AgNPs synthesized using the _C. arvensis_ leaf extract before the Cu\({}^{2+}\) ions adsorption and after, as displayed in Figure 4a. The figure presents a high-intensity peak in the optical absorption range at 3 keV for the adsorption range of AgNPs, indicating that the C. arvensis leaf extract successfully contributed to the synthesis of AgNPs. The spectrum also identifies C, O, Na, Ca, Cl, and Cd peaks, indicating that the AgNPs contain organic and inorganic compounds [8; 21; 23]. The EDS spectrum of the AgNPs after the adsorption of Cu\({}^{2+}\) (Figure 4b) presented a decrease in the percentages of the Ag, Na, and Cd elements, and the emergence of a Cu\({}^{2+}\) peak indicated the adsorption of Cu\({}^{2+}\) ions on the AgNPs' surface [23].  
The surface morphology of the AgNPs was performed using a SEM analysis before and after the Cu2+ adsorption. Spherical AgNPs were observed to form with the _C. arvensis_ leaf extract (Figure 5a), which confirmed that the synthetic AgNPs were well crystallized [6; 24]. Figure 5b also presents the change in the surface morphology of the AgNPs after the adsorption of Cu\({}^{2+}\) ions [22]. Changes in the shapes of the crystals and the pores on the surface were observed, as well as the surface coverage after the adsorption of most Cu\({}^{2+}\) ions [22; 25].  
Figure 3: A Fourier-transform infrared spectroscopy (FTIR) analysis of the functional groups in AgNPs before and after Cu\({}^{2+}\) was adsorbed.  
Figure 4: Energy-dispersive X-ray spectroscopy (EDS) images of AgNPs (0.2 g) before (**a**) and after Cu\({}^{2+}\) (10 mg/L) was adsorbed (**b**) for 3 h at 298 K.