Abstract
This study presents a relatively low-cost method for modifying TiO(2)-based materials for photocatalytic bacterial inactivation. The photocatalytic inactivation of Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus epidermidis) bacteria using modified sulphated TiO(2) was studied. The modification focused on the reduction of TiO(2) by ammonia agents and hydrogen at 400-450 °C. The results showed a high impact of sulphate species on the inactivation of E. coli. The presence of these species generated acid sites on TiO(2), which shifted the pH of the reacted titania slurry solution to lower values, around 4.6. At such a low pH, TiO(2) was positively charged. The ammonia solution caused the removal of sulphate species from TiO(2). On the other hand, hydrogen and ammonia molecules accelerated the removal of sulphur species from TiO(2), as did heating it to 450 °C. Total inactivation of E. coli was obtained within 30 min of simulated solar light irradiation on TiO(2) heat-treated at 400 °C in an atmosphere of Ar or NH(3). The S. epidermidis strain was more resistant to photocatalytic oxidation. The contact of these bacteria with the active titania surface is important, but a higher oxidation force is necessary to destroy their cell membrane walls because of their thicker cell wall than E. coli. Therefore, the ability of a photocatalyst to produce ROS (reactive oxidative species) will determine its ability to inactivate S. epidermidis. An additional advantage of the studies presented is the inactivation of bacteria after a relatively short irradiation time (30 min), which does not often happen with photocatalysts not modified with noble metals. The modification methods presented represent a robust and inexpensive alternative to photocatalytic inactivation of bacteria.