Green synthesis and evaluation of n-type ZnO nanoparticles doped with plant extract for use as alternative antibacterials

Abstract

Emergence of resistance to antibiotics in bacterial pathogens and prevalence of residual effects of drugs pose serious challenges to public health worldwide. Diminishing efficacy of antibiotics calls for an expedited development of alternative antimicrobials. In this regard, zinc oxide (ZnO) nanoparticles (NPs) signify a latent and versatile inorganic nanostructure that possesses enhanced antimicrobial effects. In the present study, green synthesis of n-type ZnO-NPs was undertaken, which was then doped with various concentrations of extracts from ginger and garlic roots. The synthesized product was applied in low and high dosage to evaluate its antimicrobial efficacy against pathogenic E. coli. The results were compared to those obtained from chemically synthesized ZnO. Characterization of NPs was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy (UV–Vis), field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HR-TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) emission. Strong absorption at 362 nm was observed for green synthesized NPs. HR-TEM exhibited interlayer spacing of 0.317, 0.312 and 0.308 nm, which is consistent with XRD results. Significant inhibition zones of 2.95–4.00 mm were observed for ZnO-NPs doped with ginger extract at an optimized concentration of 6 ml: 1. Similarly, garlic-doped NPs exhibited 1.85 and 2.75 mm inhibition zones at low and high dosage, respectively. The photodegradation study of synthesized products was undertaken using methylene blue (MB) dye under visible light source, where ZnO exhibited nearly complete decolourization of MB dye following a pseudo-first-order kinetics. The present study exemplifies an eco-friendly green nanomaterials synthesis technique using natural products (i.e., garlic and ginger), which can be expanded to include other green synthesized metal oxide NPs.