Characterization and Antibacterial Activity Study of Hydrothermally Synthesized h-MoO3 Nanorods and α-MoO3 Nanoplates

A nanostructured material is a newly emerging field in healthcare environment application because it exhibits strong antibacterial activity by preventing bacterial growth as bacteria are gradually becoming antibiotic resistant. In this article, a potential candidate of antibacterial material, molybdenum trioxide (MoO3), having two phases: the hexagonal and orthorhombic nanocrystals, were successfully synthesized by facile hydrothermal method. Then, the structural, morphological, functional, and optical properties of both h-MoO3 nanorods and α-MoO3 nanoplates were characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), Fourier-transform infrared spectroscopy (FTIR), and UV-Vis-NIR spectrophotometer, respectively. XRD patterns revealed hexagonal to orthorhombic phase transition after annealing at 450 °C for 2 h, supported by FTIR spectra. The micrograph analysis by FESEM also confirmed the 1D hexagonal nanorod structure collapsed and converted into two-dimensional (2D) plate-like orthorhombic structure after annealing. The crystallite size and optical bandgap increased from 35 to 135 nm and 2.83 to 2.87 eV, respectively, after phase transformation. The antibacterial activities of both samples were assessed against two Gram-positive bacteria viz. Bacillus subtilis and Staphylococcus aureus and two Gram-negative viz. Escherichia coli and Salmonella enteritidis by agar well diffusion method. The hexagonal nanorods exhibited more activity compared with nanoplates. It was found that the antibacterial activity of the nanoparticles decreased with increasing crystallite size.