Comparative study on sol-gel combined with a hydrothermal synthesis of ZnAl2O4 and ZnO/ZnAl2O4 nanocomposites and its photoluminescence properties and antibacterial activity

Zinc oxide-based composite nanomaterials were successfully synthesized by a simple sol-gel combined with a hydrothermal synthesis method. X-ray powder diffraction and Fourier transform infrared spectroscopy results confirm that the zinc oxide-based composite nanomaterials only corresponding metal oxides exist in the samples and not contain any other impurities. Scanning electron microscopic images shows that the ZnO/ZnAl2O4 composite materials are composed of fine nanoparticles and rhombic fine particles. Compared with ZnAl2O4 and ZnO, ZnO/ZnAl2O4 composite materials have a wider light absorption capacity, suggesting that the ZnO/ZnAl2O4 composite materials have a high antibacterial activity. Fluorescence spectrum analysis reveals that the ZnO/ZnAl2O4 composite materials have higher charge transfer and separation efficiency in visible light range, indicating that its has high antibacterial activity. Three obvious emission peaks at 372, 420 and 430 nm can be found for the ZnO/ZnAl2O4 composite materials with excitation wavelength of 250 nm. Staphylococcus aureus and Escherichia coli were selected as the representatives of gram-positive and negative bacteria, respectively, and the antimicrobial properties of ZnO/ZnAl2O4 composite materials were evaluated. The ZnO/ ZnAl2O4 composite materials exhibits higher photocatalytic inactivation rate than previously reported due to the synergistic effect of mass ratio of ZnO to ZnAl2O4, preparation method, specific surface area, light absorption capacity, charge transfer and separation efficiency. Based on experimental and theoretical analysis, a possible photocatalytic inactivation mechanism of ZnO/ZnAl2O4 composite materials was proposed.