Antimicrobial property and photocatalytic antibacterial mechanism of the TiO2-doped SiO2 hybrid materials under ultraviolet-light irradiation and visible-light irradiation

In this study, an antibacterial hybrid material of TiO2-doped SiO2 (TiO2@SiO2) was prepared by hydrolysis, where the SiO2 carrier was synthesized by a sol–gel method. The as-prepared antibacterial materials were characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller measurements and particle size analysis. The antibacterial effect of the prepared hybrid materials on Escherichia coli (E. coli) was investigated by the plate coating method. The presence of the Ti–O–Si bond between anatase-TiO2 and SiO2 was confirmed by the above characterization methods, which was beneficial to enhance the photocatalytic inactivation effect of E. coli under ultraviolet-light (UVA) irradiation and visible-light irradiation. With the increase in the TiO2 content from 1.5% to 4.4%, antibacterial activities were clearly enhanced under different types of light irradiation. For the optimum sample of 4.4%-TiO2@SiO2, antibacterial rates of 99.3% and 90.5% under UVA irradiation and visible-light irradiation were obtained, respectively. The antibacterial mechanism was demonstrated by fluorescence detection of the reactive oxygen species (ROS) and SEM images of the changes in the bacterial morphology. Results revealed that the hybrid materials can generate ROS under not only UVA irradiation but also visible-light irradiation. A majority of the ROS migrated into the bacterial cells and caused the oxidative damage of cells. This is a crucial study for the photocatalytic inactivation mechanism of the bacteria under both UVA and visible-light irradiation.