Plant-Mediated Green Synthesis, Characterization and Applications of ZnO, BiO Nanoparticles and Their Zn-BiO Nanocomposite

This study reports an eco-friendly green synthesis of zinc oxide (ZnO), bismuth oxide (BiO), and Zn–BiO nanocomposite using Hydrocotyle verticillata leaf extract as a natural reducing and stabilizing agent. This plant-mediated approach eliminates toxic chemicals and offers a simple, cost-effective, and sustainable route for synthesizing multifunctional nanomaterials. The nanoparticles were characterized using UV–Visible spectroscopy, FT-IR, XRD, FESEM, EDX, and TGA to evaluate their structural, optical, morphological, and thermal properties. UV–Visible analysis showed strong UV absorption for ZnO and enhanced visible absorption for BiO, while the Zn–BiO nanocomposite exhibited a red shift, indicating modified optical behavior. FT-IR confirmed Zn–O and Bi–O bond formation, and XRD revealed well-defined crystalline structures with nanoscale crystallite sizes. TGA demonstrated good thermal stability, with the nanocomposite showing improved stability due to strong interfacial interactions. FESEM images indicated distinct morphologies and better dispersion in the composite, while EDX confirmed elemental composition and high purity. Antibacterial studies showed moderate activity of ZnO against Escherichia coli and stronger activity of BiO against Bacillus subtilis. Corrosion studies revealed ZnO performs better in alkaline medium, BiO in neutral medium, and Zn–BiO shows superior inhibition in acidic conditions. Shelf-life studies demonstrated delayed vegetable spoilage, indicating effective antimicrobial performance. Overall, the Zn–BiO nanocomposite exhibits enhanced physicochemical properties and promising applications in antimicrobial, anticorrosion, and food preservation fields.