Síntese e caracterização de compostos binários no sistema TiO2:Nb2O5

Abstract

Materials science is an area of Chemistry responsible for synthesizing, developing and characterizing materials with chemical, electrical, optical, thermal, mechanical, and microstructural properties to provide the most varied technological applications. Within this area, one of the most interesting compounds is oxides, and the synthesis of binary or ternary compounds from them, can generate new properties or improve those already existing in isolated compounds. In this work, compounds were studied using Niobium Oxide V and Titanium Oxide IV. Samples of binary compounds in the TiO2:Nb2O5 system were obtained, with the following stoichiometries: 1TiO2:1Nb2O5 (TiNb2O7), 2TiO2:5Nb2O5 (Ti2Nb10O29) and 1TiO2:12Nb2O5 (TiNb24O62), using the synthesis technique by the solid-state reaction. All synthesized samples were analyzed by X-ray diffraction to determine the crystalline structure. Only samples of stoichiometric ratio 2TiO2:5Nb2O5 and 1TiO2:12Nb2O5 presented single-phase samples of Ti2Nb10O29 and TiNb24O62 compositions respectively. Both samples were identified with orthorhombic phase with lattice parameters equal to a= 28,310 Å, b = 3,777 Å, and c = 20,345 Å for Ti2Nb10O2 and a = 29,780 Å, b = 3,821 Å and c = 21,120 Å for TiNb24O62. These samples were analyzed by the TG/DSC technique, which showed a thermal event common to the compositions. An exothermic transition that starts around 500°C without mass change, is possibly associated with a confirmation of the crystalline structure to a position of equilibrium of the ions or even completion of the reaction. A second thermal event, with an exothermic process and mass gain, which only occurs in the Ti2Nb10O2 sample, may be related to the oxidation of Ti ions and oxygen assimilation by the structure. The diffuse reflectance UV/Vis spectroscopy measurements determined a band gap of 3.31 and 3.03eV for the Ti2Nb10O29 and TiNb24O62 compositions, respectively. These values are interesting for photocatalysis applications, especially the second sample with a smaller band gap, which can optimize the utilization of visible light from the solar spectrum.