## 3 Results and Discussion  
### Physicochemical Characterisation  
The XRD pattern of the biosynthesized ZnO NPs presented in Figure 2a reveals well-defined relatively broad peaks with high intensity which indicates the formation of nanocrystalline phase. The observed peaks are indexed within the hexagonal ZnO wurtzite-type structure, in agreement with Joint Committee on Powder Diffraction Standards (JCPDS) card no. 36-1451 [38]. No additional peaks can be detected within the resolution limit of the X-ray diffractometer, thereby confirming the formation of single ZnO phase. Using the Debye-Scherer formula (D = 0.9 \(\uplambda\)/\(\beta\) cos\(\theta\), where \(\theta\) is the diffraction angle, \(\uplambda\) = 1.5406 A, and \(\beta\) is the peak width at half maximum), crystallite size of prepared ZnO nanoparticles was calculated around 17 nm [38]; also, lattice parameters (a, c) were found to be about 3.306 and 5.199, respectively. The elemental information of the synthesized ZnO NPs was confirmed by EDX (Figure 2b); the spectrum indicates the existence of Zn and O elements which confirms again the purity of the prepared ZnO NPs. The analysis of EPR curve based on the calculated g-values from a spectrum formed of a symmetrical Lorentzian shape, indicated the presence of two narrow resonances: one at g-value \(\sim\)1.985 and the other at g-value \(\sim\)1.987, corresponding to shallow donors and singly ionized oxygen vacancies, respectively (Figure 2c) [47,48]. Figure 2: _Cont._  
FTIR analysis helped to identify functional groups existing in the plant extract that contribute to the mechanism of bonding with ZnO NPs. As we mentioned previously, _S. ebulus_ extract contains high amounts of polyphenolic derivatives. such as flavonoids, anthocyanins, and cyanidin-3-glucose, which are considered potential bioactive compounds for therapeutic treatments and to act as reducing agents [8; 9; 10; 11; 12; 13; 14; 15]. A comparison between the FTIR spectrum of the plant extract and that of the biosynthesized ZnO NPs is shown in Figure 2d. Accordingly, the FTIR spectrum of the plant extract exhibited several peaks at 3429, 2846, 2921, 1700, 1670, 1527, 1383, 1242, 1076, 1380, 1249, 1110, and 1024 cm\({}^{-1}\). The peaks at 3429 (O-H), 1527-1670 (N-H), and 1076 (C-O) or 880-1380 (RCOO) cm\({}^{-1}\) are related to alkaloids, flavonoids, and phenolic compounds, respectively [49; 50; 51; 52], whereas the broad stretching band at 3429 cm\({}^{-1}\) indicates the presence of hydrogen-bonded groups. These results signify the existence of flavonoid derivatives in the _S. ebulus_ extract. Any shift or change in the position and intensity of peaks in the sample spectrum can be correlated with the interaction of the functional groups of the flavonoids and phenols with the ZnO NPs. It can be mentioned that functional groups in the extract donate electrons that could reduce zinc ions (Zn\({}^{2+}\) to Zn\({}^{+1}\)) and finally zinc NPs (Zn\({}^{0}\)). Moreover, the negative functional groups present in the extract could have a stabilizing effect. FTIR spectra of the biosynthesized ZnO NPs showed a small shift with slight changes in some related peaks and in their intensities, suggesting that the major biomolecules from the extract were capped or bonded to the surface of ZnO NPs. The major peak for the plant extract shifting from 3429 to 3426 cm\({}^{-1}\) in ZnO was assigned to the O-H of the phenol groups and -NH\({}_{2}\) stretching vibrations, while another peak shifted from 1668 to 1579 cm\({}^{-1}\) was ascribed to N-H binding. The appearance of new peaks at 700 and 2212-2230 cm\({}^{-1}\) proved that ZnO NPs underwent C-H and C=C out-of-plane bending, respectively. Figure 2: (**a**) X-ray diffraction pattern; (**b**) energy-dispersive X-ray spectroscopy spectrum; (**c**) electron paramagnetic resonance (EPR) of ZnO NPs; and (**d**) Fourier-transform infrared spectroscopy spectra of ZnO nanoparticles (purple line), _S. ebulus_ extract (red line); and (**e**) typical chromatogram of the extract.