ZnO/graphite composites and its antibacterial activity at different conditions

• Composites ZnO/graphite (ZinGra) crystallite size less than 100 nm were prepared.
• Analytical methods revealed ZnO tightly anchored on the graphite matrix.
• Antibacterial properties induced by daylight were observed due to photocatalysis.
• Antibacterial properties under dark conditions were observed due to Zn2+.
• ZinGra exhibited antibacterial properties to human pathogens.

The paper reports laboratory preparation, characterization and in vitro evaluation of antibacterial activity of ZnO/graphite nanocomposites. Zinc chloride and sodium carbonate served as precursors for synthesis of zinc oxide, while micromilled and natural graphite were used as the matrix for ZnO nanoparticles anchoring. During the reaction of ZnCl2 with saturated aqueous solution of Na2CO3a new compound is created. During the calcination at the temperature of 500 °C this new precursors decomposes and ZnO nanoparticles are formed. Composites ZnO/graphite with 50 wt.% of ZnO particles were prepared. X-ray powder diffraction and Raman microspectroscopy served as phase-analytical methods. Scanning electron microscopy technique was used for morphology characterization of the prepared samples and EDS mapping for visualization of elemental distribution. A developed modification of the standard microdilution test was used for in vitro evaluation of daylight induced antibacterial activity and antibacterial activity at dark conditions. Common human pathogens served as microorganism for antibacterial assay. Antibacterial activity of ZnO/graphite composites could be based on photocatalytic reaction; however there is a role of Zn2+ ions on the resulting antibacterial activity which proved the experiments in dark condition. There is synergistic effect between Zn2+ caused and reactive oxygen species caused antibacterial activity.