Phyto-assisted synthesis and characterization of zinc oxide nanoparticles and zinc oxide copper composite nanoparticles using Curly Blumea (Laggera crispata) leaf extract and evaluation of their antibacterial activity

Development of an eco-friendly process for the synthesis of Zinc Oxide Nanoparticles (ZnO-NPs) and Zinc Oxide–Copper Nanocomposites (ZnO-Cu NCs) is an important aspect in the field of nanotechnology. Curly Blumea ( Laggera crispata ) leaf extract was utilized to synthesize ZnO-NPs and ZnO-Cu NCs. The nanoparticles were synthesized at pH 12, temperature 80 °C, and 56 mM precursor concentration showing absorption peaks at 379 nm (ZnO-NPs) and 382 nm (ZnO-Cu NCs). The synthesized nanoparticles were characterized using XRD, FTIR, SEM, DLS, and TEM. DLS revealed hydrodynamic particle sizes of 58 nm and 31.8 nm for ZnO-NPs and ZnO-Cu NCs, respectively, while TEM showed actual sizes of approximately 20 nm (ZnO-NPs) and 30 nm (ZnO-Cu NCs). XRD confirmed a hexagonal wurtzite structure with crystallite sizes of 21.5 nm (ZnO-NPs) and 20.4 nm (ZnO-Cu NCs). SEM showed spherical and irregular agglomerated morphologies. The optical band gap energies were determined as 3.1 eV for ZnO-NPs and 2.82 eV for ZnO-Cu NCs. Gram-positive ( Staphylococcus aureus and Bacillus cereus ) and Gram-negative ( Escherichia coli and Morganella morganii ) bacteria were used to evaluate antibacterial efficacy. ZnO-NPs exhibited maximum zones of inhibition of 22 mm against S. aureus and 20 mm against B. cereus , while ZnO-Cu NCs showed enhanced activity with zones of inhibition of 23 mm against S. aureus and 22 mm against B. cereus . The results indicated that Gram-positive bacteria were more susceptible than Gram-negative bacteria to both nanomaterials. It is notable that although ZnO-Cu NCs showed smaller hydrodynamic diameter by DLS, they demonstrated superior antibacterial performance, which is attributed to their lower band gap energy and enhanced reactive oxygen species generation. Clinical Trial Number Not applicable