Standardized Figures of Merit for Proper Benchmarking of Photocatalytic Inactivation of Bacteria Using Thin Films Based on TiO2 Nanostructures.

The study of photocatalysts fixed to surfaces for the inactivation of bacteria in wastewater has increased in recent years. However, there are no standardized methods to analyze the photocatalytic antibacterial activity of these materials, and no systematic studies have attempted to relate this activity to the number of reactive oxygen species generated during UV-light irradiation. Additionally, studies regarding photocatalytic antibacterial activity are usually carried out with varying pathogen concentrations, UV light doses, and catalyst amounts, making it difficult to compare results across different materials. The work introduces the photocatalytic bacteria inactivation efficiency (PBIE) and bacteria inactivation potential of hydroxyl radicals (BIPHR) figures of merit for evaluating the photocatalytic activity of catalysts fixed onto surfaces for bacteria inactivation. To demonstrate their applicability, these parameters are calculated for various photocatalytic TiO2 -based coatings, accounting for the catalyst area, the kinetic reaction rate constant associated with bacteria inactivation and hydroxyl radical formation, reactor volume, and UV light dose. This approach enables a comprehensive comparison of photocatalytic films prepared by different fabrication techniques and evaluated under diverse experimental conditions, with potential applications in the design of fixed-bed reactors.

Enhanced photocatalytic bacterial inactivation of atomic-layer deposited anatase-TiO2 thin films on rutile-TiO2 nanotubes.

In this work, experimental conditions were established to fabricate self-ordered rutile-TiO2 nanotube arrays, coated with a conformal anatase-TiO2 thin layer using atomic layer deposition. E. coli inactivation tests showed a considerable increase in photocatalytic activity using rutile-TiO2 nanotubes coated with anatase-TiO2 compared to that using single rutile or anatase TiO2 nanotubes only. Photocatalytic hydroxyl radical generation rates (determined by pNDA bleaching) were also meaningfully enhanced for the combined anatase/rutile TiO2 nanostructures. Therefore, we show that it is possible to take advantage of the morphological properties of the materials and the synergic effect from the combination of both TiO2 polymorphs during the design of novel materials, which could be used as antibacterial agents to improve the quality of drinking water.