Remote Bactericidal Effect of Anatase TiO2 Photocatalytic Nanoparticles Annealed with Low-Temperature O2 Plasma

The remote bactericidal effect of TiO2 photocatalyst, i.e., the bactericidal effect away from the photocatalyst, was successfully achieved using a humidified airflow. The TiO2 photocatalyst used was anatase-type TiO2 nanoparticles (NPs) annealed with a low-temperature O2 plasma. For comparison, anatase-type TiO2 NPs annealed in the air were used. The bacteria, Bacillus subtilis, were placed away from the TiO2 NPs. The plasma-assisted-annealed TiO2 NPs significantly inactivated 99% of the bacterial cells in 5 h, whereas the pristine and air-annealed TiO2 NPs inactivated 88-90% of the bacterial cells. The remote bactericidal effect of plasma-assisted-annealed TiO2 NPs would be attributed to a larger amount of H2O2 molecules traveled by the airflow from the TiO2 NPs. The molecules were generated by chemically reacting more photoexcited carriers on the TiO2 surface with H2O and O2 in the airflow. These photoexcited carriers originated from more oxygen-based species adsorbed and more oxygen vacancies introduced on the TiO2 surface by the plasma-assisted-annealing.