## 3 Results and Discussions
### UV-Vis Spectroscopy  
The UV-visible spectroscopy measurements provide information about the optical properties of green ZS-ZnO-NPs. ZnO-NPs have excellent UV absorption properties in the range of 200-400 nm, which make them suitable for various medical applications, such as  
Figure 8: FTIR spectrum of the transmittance of ZS-ZnO-NPs synthesized using different zinc salts and a plant extract of _Phoneix dactylifera_ L at pH 12: (a). ZnCl\({}_{2}\), (b). ZnSO\({}_{4}\cdot\)H\({}_{2}\)O, (c). Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O, and (d). Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O.  
suncreens and antiseptic ointments, as they can efficiently absorb and scatter UV radiation, providing effective skin protection against harmful UV rays [81]. The UV-visible spectrum of the absorbance of the ZS-ZnO-NPs is shown in Figure 9.  
The observed absorbances generally increased with an increase in nanoparticle size. Therefore, the trend of increasing UV-vis absorbance with increasing nanoparticle size observed in this study can be attributed to the larger size of the nanoparticles synthesized using Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O followed by those synthesized using Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O, compared to those synthesized using ZnSO\({}_{4}\cdot\)H\({}_{2}\)O and ZnCl\({}_{2}\). Furthermore, the different zinc salts used in the synthesis process can also influence the optical properties of the nanoparticles, as the salts can affect the crystal structure, morphology, and surface properties of the ZS-ZnO-NPs (as shown by TEM and SEM), which can, in turn, affect their UV-visible absorbance properties. Similar studies have found that the absorption properties of nanoparticles can be affected by factors such as size, shape, and surface chemistry, as observed in biological triangular Au-NPs [82; 83], TiO\({}_{2}\)-NPs, and ZS-ZnO-NPs [84; 85]. The gap energies of nanoparticles synthesized using different methods were determined and compared, revealing a trend of lower gap energies associated with larger nanoparticle sizes, suggesting that nanoparticle size may influence their optical and electronic properties. As shown in Figure 9 (Table), ZS-ZnO-NPs synthesized using ZnCl\({}_{2}\) exhibited the highest gap energy at 3.39 eV, followed by ZS-ZnO-NPs synthesized using ZnSO\({}_{4}\cdot\)H\({}_{2}\)O at 3.36 eV, and samples synthesized using both Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O as well as Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O, showing slightly lower gap energies at 3.33 eV and 3.28 eV, respectively. This trend is attributed to the larger nanoparticle sizes (both D\({}_{\text{TEM}}\) and D\({}_{\text{SEM}}\)) being associated with lower gap energies. For instance, ZS-ZnO-NPs synthesized using ZnCl\({}_{2}\), which has the smallest D\({}_{\text{TEM}}\) and D\({}_{\text{SEM}}\) sizes, also exhibited the highest gap energy, while samples of ZS-ZnO-NPs synthesized using Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O and Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O, which have larger D\({}_{\text{TEM}}\) and D\({}_{\text{SEM}}\) sizes, showed slightly lower gap energies. These findings suggest that nanoparticle size may play a role in influencing the electronic properties, with smaller nanoparticles potentially having higher gap energies.  
Figure 9: UV-visible spectrum of the absorbance and band gap energies (E\({}_{\text{g}}\), inside) of ZS-ZnO-NPs synthesized using different zinc salts and a plant extract of _Phoenix dactylifera_ L. at pH 12: (a). ZnCl\({}_{2}\), (b). ZnSO\({}_{4}\cdot\)H\({}_{2}\)O, (c). Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O, and (d). Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O.