Bactericidal action of Al 2 O 3 , Ag/Al 2 O 3 and AgCl/Al 2 O 3 on pure culture of Escherichia coli K 12 was studied. Ag/Al 2 O 3 and AgCl/ Al 2 O 3 demonstrated a stronger bactericidal activity than Al 2 O 3 . The colony-forming ability of E. coli was completely lost in 0.5 min on both of Ag/Al 2 O 3 and AgCl/Al 2 O 3 at room temperature in air. The configuration of the bacteria on the catalyst surface was observed using scanning electron microscopy (SEM). Reactive oxygen species (ROS) play an important role in the expression of the bactericidal activity on the surface of catalysts by assay with O 2 /N 2 bubbling and scavenger for ROS. Furthermore, the formation of CO 2 as an oxidation product could be detected by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and be deduced by total carbon analysis. These results strongly support that the bactericidal process on the surface of Ag/Al 2 O 3 and AgCl/Al 2 O 3 was caused by the catalytic oxidation.

The bactericidal process of Ag/Al 2 O 3 to Escherichia coli has been investigated to clarify the bactericidal mechanism. In SEM images, the configuration of E. coli cells contacting with the catalyst surface was quite different from that contacting with AgNO 3 solution, which indicated that the Ag + eluted from the catalyst did not play an important role in the bactericidal process. The bactericidal experiments strongly confirmed the contribution of multiform reactive oxygen species (ROS) (super oxide dismutase (SOD) and catalase as the scavengers for O 2•-and H 2 O 2 , respectively) to bactericidal effect on the catalyst surface. Furthermore, the surface modification of Ag/Al 2 O 3 by ultraviolet and formaldehyde influenced the bactericidal effect obviously, which not only confirmed the bactericidal mechanism of catalytic oxidation but also provided evidence for the synergistic effect between Ag and Al 2 O 3 on the catalyst surface.