## 3 Results and Discussions
### Xrd
Aging processes, such as coarsening and aggregation, occur, influencing the final morphology of the nanoparticles. Studies propose that metal ions, post-reduction by phytochemicals, may undergo coverage by organic compounds in these three phases for stabilization. The nucleation kinetics are closely associated with chemical reaction kinetics and molecular mechanisms. The growth mechanism of ZnO nanoparticles (ZnO-NPs) formation using various zinc salts, including ZnSO4-H2O, Zn(CH3 COO)2-2H2O, and Zn(NO3)2-6H2O and _Phoenix dactylifera_ L. extract in water involves a chemical reaction described by Equation (4) [76]: \[ \begin{split} n\text{Zn}\text{X}_{2}+2n\text{R-OH}+\text{H}_{2} \text{O}\rightarrow\text{Zn}^{2+}{}_{n}\text{(OH}^{-})_{m}\text{(H}_{2}\text{O )}l\text{X}^{-}{}_{k}+(2n-k)\text{X}^{-}+(2n-m)\text{ OH}^{-}\\ +2n\text{R}^{+}\to n\text{ZnO}+\left(l+n\right)\text{H}_{2} \text{O}+2n\text{R-X}\end{split} \] (4) In this equation: \[ \begin{split}\bullet&\text{Zn}\text{X}_{2}\text{ represents the zinc salt, where X is the anion (e.g., Cl}^{-}\text{, SO}_{4}{}^{2-}\text{, CH}_{3}\text{COO}^{-}\text{, NO}_{3}^{-}\text{).}\\ \bullet&\text{R-OH}\text{ represents the phenolic compounds in the plant extract.}\\ \bullet&\text{H}_{2}\text{O}\text{ is water.}\\ \bullet&\text{Zn}^{2+}{}_{n}\text{(OH}^{-})_{m}\text{(H}_{2} \text{O)}l\text{X}^{-}{}_{k}\text{ is the zinc-ligand molecule acting as a nucleation precursor.}\\ \bullet&\text{(2$n-m$) OH}^{-}\text{, and }2n\text{R}^{+}\text{ are byproducts.}\\ \bullet&\text{$n$ZnO is the formed zinc oxide nanoparticles.}\\ \end{split} \] The selection of different zinc salts, each accompanied by a distinct anion (X), holds significant implications for the synthesis of zinc oxide nanoparticles (ZnO-NPs). The chemical reactivity of varied anions, such as chloride (Cl\({}^{-}\)), sulfate (SO\({}_{4}{}^{2-}\)), acetate (CH\({}_{3}\)COO\({}^{-}\)), and nitrate (NO\({}_{3}\)\({}^{-}\)), influences the nucleation kinetics during the synthesis process. The anion plays a pivotal role in forming precursors, impacting the stability and reactivity of zinc-ligand molecules. Solubility differences arising from the nature of the anion affect  
Figure 7: Growth mechanism for the sustainable synthesis of zinc salt-dependent hexagonal zinc oxide nanoparticles. supersaturation levels, influencing the timing and extent of nucleation. Furthermore, the anion's role in stabilizing the formed nanoparticles and its interactions with polyphenols from the plant extract contribute to variations in the growth and termination phases. Plant polyphenols cause metals to form their metal oxides and make them reach the growth and stabilization phases. Finally, by binding metal ions to oxygen, nanoparticles with a defined shape are formed at the final treatment with the annealing temperatures [29; 75]. Hence, understanding the specific contributions of each anion is crucial for tailoring the synthesis method and achieving desired characteristics in the resulting ZnO-NPs, exemplifying the nuanced impact of anion choice on the overall nanoparticle synthesis process [76]. The crystallite size of the ZS-ZnO-NPs was estimated using the Debye-Scherrer equation [26; 45]. Therefore, the average crystallite sizes of the ZS-ZnO-NPs were in the range of 9.3 \(\pm\) 0.5 to 22.6 \(\pm\) 1.4 nm (Table 2), which were consistent with the particle sizes determined by SEM, and TEM analysis. The XRD results definitively confirm the presence of ZnO-NPs, as evidenced by distinct peaks aligning with the hexagonal structure. This affirmation underscores the purity of the synthesized nanoparticles, as no supplementary peaks indicative of impurities were observed, consistent with TEM and EDX findings (refer to Section 3.4). Furthermore, we bolstered the comprehensive characterization of the nanoparticles by employing FTIR and UV-visible spectroscopy in the following sections.