Preparation of nanostructured TiO2 films with high catalytic activity and their 3D spatial distribution of anatase and rutile phases

In this study, a facile, cheap, scalable, and environmentally friendly method has been developed to prepare nanostructured TiO₂ coatings with a high catalytic activity. In addition, a protocol to characterize the prepared films in order to obtain consistent results between their texture, their structure, their microstructure, and their catalytic behavior has been established. For that, two types of TiO₂ coatings have been fabricated by applying once TiO₂ aqueous suspensions, prepared from commercial nanopowders, by immersion followed by an adequate thermal treatment. The first type of films is constituted by coatings with anatase as single phase, and the second one by films with a rutile molar fraction of X_R = 0.07 ± 0.02, determined from grazing incidence X-ray diffraction (GI-XRD) data. High spatial resolution chemical imaging, obtained by confocal Raman microscopy (CRM), of the surface and of the cross section for the films showed a good distribution of rutile without any segregation of this phase. Furthermore, high resolution electron microscopy (HREM) confirmed the presence of anatase/rutile biphasic domains in those areas in which both phases were previously found together by CRM. In addition, the catalytic data fit to a first-order kinetic model with high catalytic reaction constants (k′), especially when rutile is present. Furthermore, consistent results have been found in this study between the textural, structural, and microstructural studied features with the catalytic properties for the prepared TiO₂ films.