Pure and lanthanum-doped zinc oxide nanoparticles: synthesis, characterization, and antibacterial activity

Pure and lanthanum-doped zinc oxide nanoparticles (Zn1-xLaxO), with atomic percentages (x = 0, 1, 3, 5 and 7 at%) were prepared by chemical co-precipitation method. The synthesized samples have been characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, photoluminescence spectroscopy (PL) and M-H loop using vibrating sample magnetometer (VSM). XRD analysis reveals the wurtzite hexagonal crystal structure of ZnO structure with the detection of lanthanum oxide secondary phase (La2O3) for x >= 3 at%. The increase of the lanthanum content affects the particles size, energy bandgap and lattice parameters. The presence of functional groups and the chemical bonding is confirmed by FTIR spectra that shows the formation of additional peaks due to ZnO ions dopant. The direct energy bandgap was calculated, showing a noticeable change as the concentration of the lanthanum content increases. The photoluminescence spectra show 8 emission peaks due to different defects. The M-H curves exhibited a combination of both diamagnetic and ferromagnetic contributions. The antibacterial activity of the synthesized samples was studied against three gram-negative (Escherichia coli, Klebsiella pneumoniae, and Citrobacter braakii) and three gram-positive (Staphylococcus aureus, Staphylococcus haemolyticus, and Streptococcus intermedius) bacterial strains using agar well diffusion method. These nanoparticles exhibited various degrees of antibacterial activity against the investigated bacteria.