Green synthesis of copper oxide nanoparticles using Holarrhena antidysentrica extract: Temperature effect and antibacterial efficacy

Fruit extract of Holarrhena antidysenterica served as a reducing agent for producing copper oxide nanoparticles (CuONPs). Thermal annealing was used to synthesize the nanoparticles at temperatures varying from 400°C to 800°C. Annealed CuONPs were subjected to structural and optical analyses using XRD, UV-Vis, HR-TEM, SEM, EDX, and FTIR. XRD and TEM measurements showed that the crystal size increased from 16.09 nm to 37.13 nm with increasing annealing temperature, along with enhanced crystallinity. UV-Vis absorption peaks between 250–300 nm showed a red shift from 250 nm to 287 nm, confirming temperature-dependent particle size control. The antibacterial effectiveness of synthesized CuONPs was tested against Escherichia coli , Staphylococcus aureus , and Salmonella enterica . The CuONP400 sample exhibited the highest zone of inhibition, measuring 18 mm against E. coli, 14 mm against S. aureus , and no activity against S. enterica . These findings demonstrate that the synthesized CuONPs exhibit significant antimicrobial effectiveness, with synergistic effects observed across different annealing temperatures.