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 plasmaassisted-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.