RESUMO
Commercially available polypropylene foil was pretreated with a low temperature oxygen plasma and covered with a thin film of nanocrystalline titanium dioxide by dip coating. The films were then photosensitized by titanium(IV) surface charge transfer complexes formed by impregnation with catechol. The photoactivity of the coatings up to 460 nm was confirmed by photoelectrochemical measurements. The photoinactivation of Escherichia coli and Staphylococcus aureus was evaluated by a glass adhesion test based on ISO 27447:2009(E) in the presence of visible light. The coating showed good antimicrobial activity induced by light from a light-emitting diode (405 nm), in particular towards E. coli ATCC 25922 strain. Adaptation of ISO 27447:2009(E) to assess bacterial photoinactivation by photocatalytic coatings will allow this procedure to be applied for the comparison of photoactivity under a range of irradiation conditions.
Assuntos
Escherichia coli/fisiologia , Luz , Viabilidade Microbiana/efeitos dos fármacos , Viabilidade Microbiana/efeitos da radiação , Polipropilenos/farmacologia , Staphylococcus aureus/fisiologia , Titânio/química , Catálise , Escherichia coli/efeitos dos fármacos , Escherichia coli/efeitos da radiação , Fármacos Fotossensibilizantes/química , Fármacos Fotossensibilizantes/farmacologia , Polipropilenos/química , Staphylococcus aureus/efeitos dos fármacos , Staphylococcus aureus/efeitos da radiação , Propriedades de SuperfícieRESUMO
The generation of singlet oxygen in aqueous colloids of nanocrystalline TiO2 (anatase) modified by organic chelating ligands forming surface Ti(IV) complexes was studied. Detailed studies revealed a plausible and to date unappreciated influence of near-infrared irradiation on singlet oxygen generation at the surface of TiO2. To detect (1)O2, direct and indirect methods have been applied: a photon counting technique enabling time-resolved measurements of (1)O2 phosphorescence, and fluorescence measurements of a product of singlet oxygen interaction with Singlet Oxygen Sensor Green (SOSG). Both methods proved the generation of (1)O2. Nanocrystalline TiO2 modified with salicylic acid appeared to be the most efficient photosensitizer among the tested materials. The measured quantum yield reached the value of 0.012 upon irradiation at 355 nm, while unmodified TiO2 colloids appeared to be substantially less efficient generators of singlet oxygen with the corresponding quantum yield of ca. 0.003. A photocatalytic degradation of 4-chlorophenol, proceeding through oxidation by OHË, was also monitored. The influence of irradiation conditions (UV, vis, NIR or any combination of these spectral ranges) on the generation of both singlet oxygen and hydroxyl radicals has been tested and discussed. Simultaneous irradiation with visible and NIR light did not accelerate OHË formation; however, for TiO2 modified with catechol it influenced (1)O2 generation. Singlet oxygen is presumably formed according to Nosaka's mechanism comprising O2Ë(-) oxidation with a strong oxidant (hole, an oxidized ligand); however, the energy transfer from NIR-excited titanium(iii) centers (trapped electrons) plays also a plausible role.