Role of Hydroxyl Radicals and Mechanism of Escherichia coli Inactivation on Ag/AgBr/TiO2 Nanotube Array Electrode under Visible Light Irradiation

A ternary Ag/AgBr/TiO2 nanotube array electrode with enhanced visible-light activity was synthesized by a two-step approach including electrochemical process of anodization and an in situ photoassisted deposition strategy. The dramatically enhanced photoelectrocatalytic activity of the composite electrode was evaluated via the inactivation of Escherichia coli under visible light irradiation (lambda>420 nm), whose performance of complete sterilization was much superior to other reference photocatalysts. PL, ESR, and radicals trapping studies revealed hydroxyl radicals were involved as the main active oxygen species in the photoelectrocatalytic reaction. The process of the damage of the cell wall and the cell membrane was directly observed by ESEM, TEM, and FTIR, as well as further confirmed by determination of potassium ion leakage from the killed bacteria. The present results pointed to oxidative attack from the exterior to the interior of the Escherichia coli by OH center dot, O-2(center dot-), holes and Br-0, causing the cell to die as the primary mechanism of photoelectrocatalytic inactivation.