Phyto-mediated synthesis of silver-doped zinc oxide nanoparticles from Plectranthus barbatus leaf extract: optical, morphological, and antibacterial properties

In the present study, pristine and silver-doped zinc oxide nanoparticles (ZnO and Ag-ZnO NPs) were synthesized via a simple, eco-friendly method using a Plectranthus barbatus leaf aqueous extract as an NP-generating facilitator. The NPs obtained were characterized using FTIR, XRD, SEM, and UV-Vis. FTIR confirmed chemical structure, XRD emphasizes retained hexagonal crystallite structure, SEM revealed a nanosheet morphology, and optical analysis indicated bandgap improvement from 2.55 to 2.51 and 2.04 eV for pristine, 0.02, and 0.06 Ag-doped ZnO NPs. Antibacterial test, performed on Staphylococcus aureus and Escherichia coli, representing Gram-positive and Gram-negative bacteria, using the disk diffusion method in reference to azithromycin standard drug, noticeably revealed selective action for S. aureus with negligible activity against E. coli. The activity against S. aureus was found to be concentration- and doping-dependent, and as they increased, the activity increased as well. Such improvement in ZnO properties, as a result of certain morphology enhancement, makes it one suitable nominee for applications in various fields, such as solar cells, photocatalysis, and antibacterial applications.