Continuous Photocatalytic Antibacterial Activity of AgNPs doped TiO2 Digital Printed on Commercial Porcelain-grès Tiles

Photocatalytic finishing materials, such as tiles or paints, are a productive as well as scientific reality. One of the most interesting photocatalytic material currently on the market is the porcelain stoneware which combines the beauty of a design product with hardness and absence of porosity and thus used for both floors and walls. The Ag- micrometric TiO2 allowed active ceramic slabs to be active under LED lights, bypassing the problem of the UVA radiation. SEM/TEM images in Fig. 1 indicate the full coverage of the porcelain surface (left image), besides a nanometric though heterogenous spreading of the AgNPs on top of the TiO2 matrix (right image). Figure 1. HR-SEM of the Active ceramic surface (left), TEM image of 8% AgNPs-TiO2(center); possible photocatalytic mechanistic pathways in Ag doped TiO2 system (right) An important question concerns the antibacterial action: in fact, today the role of silver is unknown when the metal is physically blocked on a surface and cannot penetrate and therefore interfere at the DNA level in the cellular barrier. The prepared porcelain Ag-TiO2 printed surfaces were tested against E. coli under solar and visible illumination and in the dark. To differenciate the semicondutor behavior and the ions mediated bacterial inactivation mechanism, porinless E. coli were used under band-gap irradiation. Stereomicroscopy analysis showed dead bacteria within 180 and 240 min respectively for normal E. coli and porinless E. coli. Using appropriate quenchers, the bacterial inactivation mechanisms under solar and visible light are proposed.