Synthesis of zinc oxide nanoparticles using Chrysopogonzizanioides grass extract, its applications in photodegradation and antimicrobial activity

Abstract

Zinc oxide nanoparticles (ZnONPs) were synthesized using zinc nitrate hexahydrate as an oxidizer and Chrysopogonzizanioides (Vetiver) grass as a novel fuel using a green approach. The plausible mechanism of synthesis of ZnONPs is explained in detail. The X-ray diffraction pattern as well as the Rietveld refinement showed a single-phase wurtzite structure. The average crystallite size and the lattice strain were estimated using Williamson–Hall plot. The stability of the crystal lattice was confirmed from the extremely small value of lattice strain. The presence of various functional groups in the plant extract and the zinc–oxygen bonding in the ZnONPs were confirmed by FTIR. The surface morphology was investigated using SEM, and it showed a nanorod-like nanostructure. The elemental mapping was carried out using EDS. The EDS spectrum suggests the formation of ZnO nanorods along with the high proportion of carbon and low proportion of Si as well as K. These might have resulted from the rich organic profile of Chrysopogonzizanioides grass extract. Within the UV–visible spectrum at 300 nm, the highly blue-shifted strong absorption band was observed due to the strong quantum confinement effect with the band gap of 3.628 eV. The photodegradation of RB2 dye was studied over ZnONPs catalyst, and it showed excellent photocatalytic activity. The catalyst was active for up to five cycles without losing much of its efficiency. The detailed degradation mechanism of RB2 dye was explained using LCMS technique. Further antimicrobial activity was tested against a broad range of microorganisms, namely Staphylococcus aureus, Escherichia coli and much prevalent human fungal pathogen Candida albicans. The minimum inhibitory concentration (MIC) for each micro-organism was determined using broth micro-dilution assay, and the values were found to be for E. coli (1.0 mg/mL IC100), S. aureus (0.5 mg/mL IC 70) and the fungal strain in planktonic growth state (0.5 mg mL-1 IC 100).