Antibacterial and Biofilm-Preventive Photocatalytic Activity and Mechanisms on P/F-Modified TiO₂ Coatings

Photocatalytic antibacterial and biofilm-preventive activity in liquid of heavy-metal-free coatings based on a phosphorus (P)- and fluorine (F)-modified TiO₂ 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 TiO₂ 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 TiO₂ coating compared to about 50% on P25 TiO₂ 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.