Estudo de filmes finos e materiais particulados de TiO2 e de Ag/TiO2 produzidos pelo processo sol-gel

Abstract

In this work, a study of physical-chemistry properties of materials consisting of TiO2 and Ag/TiO2 produced by sol-gel method was accomplished. Thin films and particulate materials were prepared from alcoholic solutions containing titanium isopropoxide (IV) as precursorfor TiO2 and AgNO3 for metallic silver. Additionally, ultraviolet light (UV-C / 254 nm) was used to promote the reduction of Ag+ ions in the sol formed. The films were produced by dip-coating process and the heat treatment employed generated structural, morphological and textural modifications in these films, which are dependent on factors as type of substrate, cooling rate and concentration of silver used. These changes were studied using high-resolution microscopy techniques that provide information about crystallinity, size and shape of nanoparticles of TiO2 and Ag. It was also possible monitoring the growth processand the segregation of Ag nanoparticles in the TiO2matrix. Crystalline phase transitions were observed in-situ in the transmission electron microscopy when amorphous Ag/TiO2 thin films were irradiated by an electron beam of 200 kV. Nanoindentations performed inTiO2 and Ag/TiO2 thin films have provided important mechanical information as the Young's modulus and hardness. The Spectroscopic Ellipsometry technique was useful in the evaluation of optical properties as refractive index, extinction coefficient, optical thickness and roughness of the films studied. It was also possible to evaluate the variation in the band gap values of TiO2 with the inclusion of silver nanoparticles. Hydrophobic/hydrophilic, antibacterial and anti-corrosion properties were tested in TiO2 and Ag/TiO2 thin films. The precursor solutions of films after gelation process and heat treatment produced pure TiO2powder and TiO2 with nano and microcrystals of silver on its surface. These particulate materials were characterized using various techniques that made it possible to evaluate the textural, structural and morphological evolution with the temperature. The morphology ofthe Ag crystals was templated by the porous network of the TiO2 matrix and these crystals showed many crystallographic forms. The photocatalytic activity of TiO2 and Ag/TiO2 samples were tested and the ability to absorb ultraviolet was performed by TiO2 samples.