## 4 Conclusions  
In summary, this study presents an efficient and sustainable synthesis of zinc salt-dependent zinc oxide nanoparticles (ZS-ZnO-NPs) utilizing diverse zinc salts (ZnCl\({}_{2}\), ZnSO\({}_{4}\cdot\)H\({}_{2}\)O, Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O, and Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O) and plant extracts from _Phoenix dactylifera_ L. The comprehensive evaluation covered the morphology, optical properties, stability, and antioxidant activity of the nanoparticles. Zeta potential measurements, SEM, TEM, XRD, UV-Vis spectroscopy, and FTIR analyses collectively confirmed the crystalline nature, size distribution, and chemical groups on the nanoparticle surface. The comprehensive analysis of the synthesized ZS-ZnO-NPs revealed significant variations influenced by the choice of zinc salt. The nanoparticles exhibited sizes ranging from 3.7 to 10.2 nm, showcasing a clear size trend (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). The zeta potential trend (ZnSO\({}_{4}\cdot\)H\({}_{2}\)O \(<\) Zn(CH\({}_{3}\)COO)\({}_{2}\cdot\)2H\({}_{2}\)O \(<\) Zn(NO\({}_{3}\))\({}_{2}\cdot\)6H\({}_{2}\)O \(<\) ZnCl\({}_{2}\)) further emphasizes the impact of the zinc salt on surface charge. The XRD results indicated distinct crystalline properties, with a notable trend (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) in average crystallite size and corresponding trends in FWHM and crystallinity (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). These trends highlight the critical role of the selected zinc salt in shaping the yield, stability, and structural characteristics of the nanoparticles. Correlating these findings, a clear relationship emerged between the choice of zinc salt and both nanoparticle size and crystalline structure. Notably, ZnCl\({}_{2}\) exhibited the smallest size and the highest crystallinity, aligning with its specific zinc salt properties. Moreover, the observed concentration and time-dependent inhibitory activity against DPPH free radicals further accentuates the potential applications of these nanoparticles across various industries. This study offers valuable insights into tailoring ZS-ZnO-NPs for diverse applications, including nutraceuticalals, pharmaceuticals, cosmetics, biofuels, and environmental sectors. Further research under physiological conditions will provide additional support for potential biomedical and medical applications. This study underscores the significance of merging biochemistry and engineering tools for efficient bioprocesses. It sheds light on the critical role of the chosen zinc salt in green synthesis, offering insights into various potential applications such as environmental remediation, (opto)electronics, nanomedicine, sensors, energy, detectors, green energy, and biotechnology. While contributing substantially to the synthesis and characterization of zinc oxide nanoparticles, ongoing research is imperative to address challenges and expand practical implications. The technology-driven green methods introduced here hold broad relevance across industries, necessitating further research to assess toxicity and broaden the scope of this work. As we explore the multifaceted realm of ZnO-NPs, produced through the green synthesis method utilizing _Phoenix dactylifera_ L. polyphenols with varied salt compositions, focusing on the anion effect, it is vital to assess their properties without the presence of the _Phoenix_ polyphenol extract. This evaluation is crucial for a deeper understanding in future research, steering clear of reliance on chemically synthesized ZnO-NPs.