Antibacterial and Biofilm-Preventive Photocatalytic Activity and Mechanisms on P/F-Modified TiO 2 Coatings.

Photocatalytic antibacterial and biofilm-preventive activity in liquid of heavy-metal-free coatings based on a phosphorus (P)- and fluorine (F)-modified TiO 2 photocatalyst has been investigated. They reveal significantly higher immediate and longer-term (biofilm-preventive) inactivation capacity than a reference coating made of the commercial photocatalyst TiO 2 P25 on three bacterial species differing in cell wall type and ability to resist oxidative stress ( Escherichia coli , Staphylococcus epidermidis , Pseudomonas fluorescens ) (up to more than 99% reduction of colonization on P/F-modified TiO 2 coating compared to about 50% on P25 TiO 2 coating for 10 min UV-A illumination). This results from the P- and F-induced improvement of photocatalyst properties and from the smoother surface topography, which shortens reactive oxygen species (ROS) diffusion to the outer membrane of the targeted adhered bacteria. Decrease in ROS-related impairment of cell wall, respiratory, and enzymatic activities confirms the loss of ROS throughout the bacterial cell degradation. Staphylococcus epidermidis and Pseudomonas fluorescens are less sensitive than Escherichia coli , with a probable relation to the bacterial oxygen stress defense mechanism. The coating antibacterial efficacy was highly affected by phosphate ions and the richness in dissolved oxygen of the reaction medium.