## 3 Results and Discussions
### TEM  
The effect of different zinc salts on the morphology (Figure 4) and size distribution of ZS-ZnO-NPs was investigated using a green synthesis method under the same conditions.  
Figure 4: Transmission electron microscopy (TEM) and the respective elemental energy-dispersive X-ray spectroscopy (EDX) analysis 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\({}_{4}\)-H\({}_{2}\)O, (**c**). Zn(CH\({}_{3}\)COO)\({}_{2}\)-2H\({}_{2}\)O, and (**d**). Zn(NO\({}_{3}\))\({}_{2}\)\(\cdot\)6H\({}_{2}\)O. Diameter distribution from TEM images was included.  
The nanoparticles exhibited diverse morphologies with weakly differentiated agglomeration in various shapes, which can be attributed to the flower-like behavior and elongation caused by the competition between the functional compounds and zinc-dependent ions on the particle's surface [20; 53]. Elemental analysis using EDX revealed no presence of elements other than O-Zn in the samples (Figure 4). The diverse morphologies observed in ZS-ZnO-NPs, as determined by fast Fourier transform (FFT), can be attributed to the distinct influence of various zinc salts used during synthesis. In the case of ZnCl\({}_{2}\), the hexagonal-centered cub-like shapes with facets and star-shaped morphology may be linked to the smaller ionic radius of chloride ions (approximately 181 pm) [60], promoting strong electrostatic interactions and influencing nucleation and growth. ZnSO\({}_{4}\cdot\)H\({}_{2}\)O resulted in the formation of hollow spherical structures, nanorings, and spheroidal morphology, likely due to the larger ionic radius of sulfate ions (approximately 211 pm) [60], introducing steric hindrance and impacting nanoparticle arrangement. Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O promoted the formation of larger particles with faceted morphology and triclinic symmetry, with the variable ionic radius of acetate ions influencing growth processes. Lastly, Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O produced larger particles with a single crystal structure, possibly influenced by the ionic radius of nitrate ions (approximately 190 pm). This comprehensive understanding underscores the size-dependent effects of different anions on the resulting morphology of ZS-ZnO-NPs [61; 62].  
The size distribution of the ZS-ZnO-NPs followed the order of ZnCl\({}_{2}<\) ZnSO\({}_{4}\cdot\)H\({}_{2}\)O \(<\) Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O \(<\) Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O, with very small particle sizes ranging from 3.7 to 10.2 nm (Figure 5). Similar morphologies have been reported in the previous literature [63; 64; 65; 66]. The results suggest that the choice of zinc salt has a significant impact on the morphology and size distribution of ZS-ZnO-NPs, with some salts promoting the formation of small, well-defined nanoparticles, while others promote the formation of larger, more complex nanoparticles with a variety of crystal symmetries.  
The TEM results agree with SEM regarding the effect of the metal salt on the particle size distribution, but the measurements are notably smaller than those obtained via SEM. The difference in particle size measurements between SEM and TEM can be attributed to different imaging techniques and sample preparation methods. Inconsistent calibration and variations in contrast production among microscopes can exaggerate particle size in SEM. In contrast, the sample preparation technique, such as smearing a dispersion droplet on an SEM stub using a conductive coating for SEM or applying a dispersion drop onto a holey carbon-coated copper for TEM, can lead to bias towards smaller sizes for TEM [67]. These factors can lead to discrepancies between the two techniques, making it essential to carefully evaluate and consider the results obtained by both methods.