Effect of Zinc Precursors on the Antibacterial and Photocatalytic Applications of Green Synthesized ZnO Nanostructures Using Calluna vulgaris

In this study, we report the environmentally friendly green synthesis of zinc oxide (ZnO) nanostructures using Calluna vulgaris (C. vulgaris) leaves extract. The extract was used as a reductant and stabilizer in aqueous medium instead of chemicals and two different precursors, zinc acetate dihydrate and zinc nitrate hexahydrate, were used to synthesize ZnO-Acetate and ZnO-Nitrate nanostructures, respectively. The optical, structural, and morphological characteristics of the green synthesized ZnO nanostructures were investigated by UV-Visible Spectroscopy (UV-Vis), X-ray diffraction (XRD), and field emission scanning electron microscopy (FE-SEM). The optical band gaps of ZnO-Acetate and ZnO-Nitrate nanostructures were obtained as 2.56 and 3.20 eV, respectively. The synthesized ZnO nanostructures were used as a catalyst in the photodegradation of methylene blue (MB) dye and showed excellent degradation activity of 99% after 150 min of UV illumination. The degradation rate constants (k) were calculated as 0.041 and 0.035 min⁻¹ for ZnO-Acetate and ZnO-Nitrate nanostructures, respectively. The antibacterial potential of the ZnO-Acetate and ZnO-Nitrate nanostructures were evaluated against Staphylococcus aureus and demonstrated good antibacterial activities, with inhibition zones of 13.5 and 18.1 mm, respectively. It was found that the optical characteristics, and surface morphology of the green synthesized ZnO nanostructures are strongly influenced by the nature of the zinc precursors and thus affects their photocatalytic and antibacterial properties. The results show that ZnO nanostructures can be synthesized with C. vulgaris leaf extracts via a green synthesis method that is cost-effective, rapid, environmentally friendly and safe, and has strong potential for antibacterial and photocatalytic applications.