Structure and antibacterial property of nano-SiO2 supported oxide ceramic

SiO2 doped samples with different cobalt loading and pure SiO2 and Co3O4 nanopowders were synthesized by the solvothermal method and their antibacterial activities were studied. The morphology and crystallinity of the powders were analyzed by scanning electron microscopy and X-ray diffractometry patterns, respectively. The increase of particle size with doping concentration was obtained for cobalt-doped samples. The optical properties were studied using UV–vis spectroscopy. Optical studies showed a blue shift in the absorbance spectrum with increasing the doping concentration. The antibacterial activities of undoped SiO2, Co-doped SiO2 and pure Co3O4 nanoparticles against a Gram-negative bacterium Escherichia coli (E. coli, ATCC 25922) and a Gram-positive bacterium Staphylococcus aureus (S. aureus, ATCC 29213) were investigated under UV illumination and in the dark condition. Bactericidal effects were determined by the minimum inhibitory concentration (MIC) method. There was no activity for pure SiO2 and Co3O4, however, cobalt doping significantly improved antibacterial activity against both bacteria. Bacterial growth inhibition was observed under dark condition with lower efficiency than under UV illumination. The antibacterial efficiencies were affected by the physiological status of the bacterial cells, different morphologies, particle sizes and optical properties of samples.