ZnO/graphite composites and its antibacterial activity at different conditions.

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 Zn(2+) ions on the resulting antibacterial activity which proved the experiments in dark condition. There is synergistic effect between Zn(2+) caused and reactive oxygen species caused antibacterial activity.

Preparation, characterization and antibacterial properties of ZnO/kaoline nanocomposites.

This paper describes laboratory preparation, characterization and antibacterial activity testing of ZnO/kaoline composites. ZnO/kaoline composites with 50 wt.% of ZnO were laboratory prepared, dried at 105 °C and calcined at 500 °C. XRPD analysis revealed that thermal treatment caused the phase transformation of Zn containing precursor into ZnO. Scanning and transmission electron microscopy techniques were used for characterization of morphology of the prepared samples. A standard microdilution test was used for evaluation of antibacterial activity using four common human pathogens (Staphylococcus aureus, Escherichia coli, Enterococcus faecalis and Pseudomonas aeruginosa). Daylight was used for induction photocatalytically based antibacterial activity. Second possible explanation of antibacterial activity of ZnO/kaoline could be the presence of biologically available forms of zinc. During the antibacterial activity assays the ZnO/kaoline composites exhibited antibacterial activity, where differences in an onset of the antibacterial activity and activity against bacterial strains were observed. The highest antibacterial activity was observed against S. aureus, where the lowest value of minimum inhibitory concentration was determined equal to 0.41 mg/ml.