High-energy ball milling technique for ZnO nanoparticles as antibacterial material

Abstract

Nanoparticles of zinc oxide (ZnO) are increasingly recognized for their utility in biological applications. In this study, the high-energy ball milling (HEBM) technique was used to produce nanoparticles of ZnO from its microcrystalline powder. Four samples were ball milled for 2, 10, 20, and 50 hours, respectively. The structural and optical modifications induced in the 'as synthesized' nanomaterials were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and photoluminescence emission spectra (PL). SEM and TEM results show a gradual decrease in particle size from around 600 to ∼30 nm, with increased milling time. The initial microstructures had random shapes, while the final shape became quite spherical. XRD analysis showed ZnO in a hexagonal structure, broadening in the diffracted peaks and going from larger to smaller particles along with a relaxation in the lattice constant c. The value of c was found to increase from 5.204 to 5.217 Å with a decrease in particle size (600 to ∼30 nm). PL result showed a new band at around 365 nm, whose intensity is found to increase as the particles size decreases. These remarkable structural and optical modifications induced in ZnO nanoparticles might prove useful for various applications. The increase in c value is an important factor for increasing the antibacterial effects of ZnO, suggesting that the HEBM technique is quite suitable for producing these nanoparticles for this purpose.

Keywords: HEBM; SEM; XRD; ZnO nanoparticles; antibacterial; photoluminescence.

Figure 1

X-ray diffracted peaks of ZnO nanoparticles before and after ball milled for different times.

Figure 2

The value of the lattice constant c as a function of milling time.

Figure 3

Scanning electron microscope images of ZnO samples before and after milling: (A1) as purchased. (B1, C1, D1, and E1) for the samples ball milled for 2, 10, 20, and 50 hours respectively.

Figure 4

Particle size as a function of milling time.

Figure 5

Transmission electron microscope images of ZnO samples before and after milling; (A2) as purchased (B2, C2, D2 and E2) for the samples ball milled for 2, 10, 20, and 50 hours respectively.

Figure 6

Photoluminescence emission spectra of ZnO nanocrystalline samples prepared by ball milling at different times. The excitation wavelength is 325 nm. Abbreviation: PL, photoluminescence.

Figure 7

Photoluminescence intensity of the peak at 365 nm as a function of milling time (size of ZnO nanoparticles): (a) experimental curve, (b) theoretical curve. Abbreviation: PL, photoluminescence.