Microwave assisted starch stabilized green synthesis of zinc oxide nanoparticles for antibacterial and photocatalytic applications

Abstract

Nanostructured particles offer outstanding diversities of applications in the fields of nanotechnology, nano-engineering, nano-biotechnology, etc. Morphological structure, size distribution, electronic behavior including intrinsic characteristics of nanoparticles depend on the source and synthesis methods. Here, an eco-friendly approach using microwave irradiation for the synthesis of zinc oxide (ZnO) nanoparticles has been reported. Zinc nitrate was used as a precursor whereas starch and D-glucose were used as capping and reducing agent, respectively. The synthesized nanoparticles were characterized by different instrumental methods including Ultraviolet-Visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and field emission scanning electron microscopy (FE-SEM). The characteristic λ_max at 373 nm for ZnO nanoparticles was recorded from UV-Vis absorption spectrum in aqueous system. FT-IR spectrum showed a very sharp peak at 476.62 cm^-1 which confirmed the presence of Zn-O bond. The prepared ZnO was highly crystalline having wurtzite structure and the crystallite size was calculated to be 24.41 nm obtained from XRD analysis. FE-SEM images showed that the synthesized ZnO nanoparticles had near- spherical morphology and particle size was found in the range of 40-90 nm. The antibacterial and anti-biofilm application of ZnO nanoparticles were studied and inhibition zones of Gram negative Salmonella typhi (S. typhi), Klebsiella spp., Escherichia coli (E. coli) and Gram positive Staphylococcus aureus (S. aureus)- 8a were found to be 11 mm, 12 mm, 11.5 mm and 13.5 mm, respectively. Besides, ZnO nanoparticles also showed excellent photocatalytic activity against methylene blue dye solution. The easy and eco-friendly fabrication method would play vital role in other nanoparticles synthesis to meet the demand in textile industry, agriculture and medical sectors.

Keywords: Anti-bacterial activity; Anti-biofilm activity; Microwave radiation; Photocatalytic activity; Zinc oxide.

Fig. 1

Schematic presentation of ZnO NPs fabrication (A) mechanistic pathway of coordination of Zn²⁺ with glucose derivative and (B) dispersion of Zn²⁺-gluconic acid micelles within starch.

Fig. 2

Fabricated ZnO nanostructures characterization (A) UV–Visible absorption spectrum recorded in ethanol, (B) Tauc`s plot for energy bandgap, (C) functional group study of using FT-IR spectrum and (D) XRD pattern.

Fig. 3

The elemental analysis of the ZnO NPs was performed using the EDX method. (A) shows intensity (counts) of X-ray emissions vs. keV and (B) mass (%) of elements.

Fig. 4

(A) SEM image of the microwave assisted ZnO NPs and (B) its size distribution.

Fig. 5

UV-Visible spectra during degradation of MB in (A) absence and (B) presence of ZnO NPs were recorded at different time intervals under sunlight irradiation; (C) The absorbance vs. time and percentage of MB degradation vs. time plot and, (D) MB degradation kinetics.

Fig. 6

The schematic mechanistic view of photocatalytic degradation of MB by ZnO NPs under sunlight irradiation.

Fig. 7

Images of zone of inhibition of ZnO NPs suspensions against S. typhi, Klebsiella spp., E. coli and S. aureus.