Green Synthesis of ZnO Nanoparticles Using Five Medicinal Leaf Extracts: A Comparative Review on Physicochemical and Biological Properties

Abstract: Plant-mediated synthesis of zinc oxide nanoparticles (ZnO-NPs) using leaf extracts is an active research area because phytochemicals serve as eco-friendly reducing and capping agents and because ZnO-NPs show promising antibacterial and antioxidant activities. This manuscript-length summary presents a compact, standardized template that synthesizes common experimental practices used when researchers compare ZnO-NPs produced from five representative leaves (Moringa oleifera, Azadirachta indica (neem), Ocimum spp / Ocimum sanctum (tulsi), Hibiscus cannabinus / Hibiscus spp., and Citrus aurantium / Citrus spp. (orange). It describes comparative study on step-by-step extract preparation and nanoparticle formation (precursors, pH control, reaction conditions, isolation and calcination), recommended characterization workflows (UV-Vis, XRD, FTIR, and FESEM), and standardized biological testing (antibacterial activity against Staphylococcus aureus and E. coli bacteria, while antioxidant activity studied against the DPPH free radical with IC₅₀ reporting). Typical physicochemical signatures of biosynthesized ZnO-NPs are summarized (UV absorption ~ 320-380 nm; XRD wurtzite peaks at 2θ ≈ 31.7°, 34.4°, 36.2°, etc.; FTIR bands indicating phytochemical capping and Zn-O vibrations at 400-600 cm⁻¹). Finally, we present concise conclusions and a recommended reporting checklist to improve reproducibility and enable quantitative cross-study comparison.

Keywords: ZnO Nanoparticles, Moringa oleifera, Azadirachta indica (neem), Ocimum spp. (tulsi), Hibiscus spp., and Citrus aurantium.