Filmes finos híbridos de TiO2-Mo e TiO2-Cr modificados com agentes hidrofóbicos: propriedades estruturais, ópticas e de superfície

Abstract

Besides being widely used in several segments of modern industry, titanium dioxide (TiO2) has aroused great technological interest, being envisaged as a component of materials used as self-cleaning coatings. Several properties influence the self-cleaning ability of a coating, but a surface with acceptable wettability and an effective photocatalytic activity, allowing a better use of the entire spectrum of solar radiation, are determining factors in the development of a good self-cleaning surface. Promising strategies in the search for the adequacy of these morphological and structural properties may involve the TiO2 modification with metals, as well as the functionalization of its surface. With the purpose of modulating the wettability of the final material, synthesis of TiO2 thin films modified with two different types of polydimethylsiloxanes (PDMS), and through two distinct modification routes, was carried out. The samples obtained were characterized in terms of their structure, morphology, optical and surface properties. Significant variations in wettability and roughness were observed in some cases. For example, the sample calcined at 400 °C, after being modified with the vinyl-terminated PDMS, had its contact angle changed from 29° to 124°, in addition to presenting a significant increase in roughness, and a non-uniform functionalization along the surface of the film. This allowed this coating to be simultaneously hydrophobic and photocatalytic, which is very desirable.In order to modify the region of titanium dioxide radiation absorption to lower energies, TiO2 thin films modified with CrCl3 different concentrations were prepared. After structural, morphological, optical, mechanical and surface characterization of these films, it was observed that the insertion of Cr3+ to the system caused a significant modification in the properties of the final material. The sample calcined at 500 °C and containing 10% mol Cr showed a pronounced decrease in the band gap, reaching values corresponding to the region of visible radiation. The preparation of a TiO2 film simultaneously modified with CrCl3 and vinyl-terminated PDMS was also carried out, allowing the preparation of a superhydrophobic and potentially photocatalytic coating. The preparation of TiO2 thin films modified with two different types of molybdenum precursors was also carried out, in order to assess the impact of the type of molybdenum precursor on the structural, morphological, optical and surface properties of the prepared samples. It was observed that all films showed superhydrophilicity even under visible light, and that the structural, optical and morphological properties were different, depending on the molybdenum precursor used.