The effect of thermal annealing on Fe/TiO2 coatings deposited with the help of RF PECVD method. Part II. Optical and photocatalytic properties

Abstract

In this work, morphology, optical properties, photowetting effect, and bactericidal behavior of titanium dioxide coatings, both plain and iron doped within the range of 0.52 and 4.76at%, are presented. The coatings were synthesized with the help of radio frequency plasma enhanced chemical vapor deposition technique followed by thermal annealing at 500°C under normal atmospheric conditions. Atomic force microscopy examination of the film morphology reveal roughness differences depending on the concentration of iron. Measurements of optical properties, carried out with the UV–VIS absorption spectrometry, show high transmittance in the visible range. Optical gap values, determined with the help of the Tauc equation, exhibit a decreasing tendency with an increasing iron content, but only up to the concentration of 2.5at%, with thermally annealed coatings characterized by higher Eg values than those of the non-annealed materials. Results of variable angle spectroscopic ellipsometry measurements indicate that both iron doping and thermal annealing have the effect of increasing refractive index of the films. An analysis of the coatings surface wettability, performed under conditions of an alternative exposure either to daylight or to the UV-B radiation, show the most important parameter to be the time of water contact angle return to its initial value under darkroom conditions. Finally, bactericidity studies of the UV-B irradiated samples, performed with the Escherichia coli DH5α bacteria, reveal the most extensive bactericidal effect observed for low iron concentrations, equally for both non-annealed and thermally annealed materials.