Green Synthesis of Novel Rhododendron arboreum-Based Zinc Oxide Nanoparticles for Enhanced Antimicrobial and Photocatalytic Degradation Activities

Zinc oxide nanoparticles (ZnO NPs) are becoming an innovative agent in biological and environmental applications due to its unique characteristics, biocompatibility, low cost and toxicity. In this study, the composite ZnO NPs using Rhododendron arboreum (R. arboreum) stem bark were synthesized and characterized for UV–visible spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The biomedical assessment of the synthesized nanoparticles showed zones of inhibition of 23 ± 0.09, 18 ± 0.1 and 16 ± 0.05 mm, against the Klebsiella pneumoniae (K. pneumoniae), Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) strains, respectively. Likewise, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values against K. pneumoniae, S. aureus, and E. coli were found to be 34 ± 0.21 and 72.71 ± 0.47, 47 ± 0.11 and 94.86 ± 0.84 and 94 ± 0.18 and 185.43 ± 0.16 µg/mL, respectively. The biosynthesized ZnO NPs resulted in significant eradication of the outer and inner membranes of the tested bacterial cells. In addition, the environmental application of the synthesized ZnO NPs also showed time-dependent photocatalytic degradation activity and revealed 65% methyl orange dye degradation with an irradiation period of 6 h. The findings of this study suggest the suitability of the novel R. arboreum stem bark-based ZnO NPs as an effective ameliorant against bactericidal activities and photocatalytic potential for the removal of potentially toxic substances from water.