New evidence for TiO2 uniform surfaces leading to complete bacterial reduction in the dark: Critical issues

Abstract This study presents new evidence for the events leading to Escherichia coli reduction in the absence of light irradiation on TiO 2 -polyester (from now on TiO 2 -PES. By transmission electron microscopy (TEM) the diffusion of TiO 2 NP's aggregates with the E. coli outer lipo-polyssacharide (LPS) layer is shown to be a prerequisite for the loss of bacterial cultivability. Within 30 min in the dark the TiO 2 aggregates interact with E. coli cell wall leading within 120 min to the complete loss of bacterial cultivability on a TiO 2 -PES 5% TiO 2 sample. The bacterial reduction was observed to increase with a higher TiO 2 loading on the PES up to 5%. Bacterial disinfection on TiO 2 -PES in the dark was slower compared to the runs under low intensity simulated sunlight light irradiation. The interaction between the TiO 2 aggregates and the E. coli cell wall is discussed in terms of the competition between the TiO 2 units collapsing to form TiO 2 -aggregates at a physiologic pH-value followed by the electrostatic interaction with the bacteria surface. TiO 2 -PES samples were able to carry repetitive bacterial inactivation. This presents a potential for practical applications. X-ray photoelectron spectroscopy (XPS) evidence was found for the reduction of Ti 4+ to Ti 3+ contributing to redox interactions between TiO 2 -PES and the bacterial cell wall. Insight is provided into the mechanism of interaction between the E. coli cell wall and TiO 2 NP's. The properties of the TiO 2 -PES surface like percentage atomic concentration, TiO 2 -loading, optical absorption, surface charge and crystallographic phases are reported in this study.