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Natalia LaptashInstitute of Chemistry, Far Eastern Branch of RASFluoride And Oxide Fluoride Compounds During Fluoride Processing Of Titanium-containing Raw Materials Tressaud International Symposium on Solid State Chemistry for Applications and Sustainable Development Back to Plenary Lectures » |
Abstract:Titanium dioxide (TiO2) is one of the most attractive materials during the last decades because of its variety of practical applications such as photocatalysis, amphiphilic coatings, and dye-sensitized solar cells. So far, numerous TiO2 nanostructures have been prepared such as spheres, films, nanowires, nanofibers, and nanotubes. In addition to the trend of nanostructural fabrication, the microarchitecture of TiO2 has become a new paradigm in recent materials, chemistry, and nanotechnology [1]. Ammonium oxofluorotitanate (NH4TiOF3) crystals have been intensively studied and used as precursors for the synthesis of highly ordered and morphologically controlled TiO2 [2]. It has been found that co-doping of nonmetal (especially with N and F) and metal (Fe) elements is capable of extending the light absorption edge of TiO2 to the visible light region and improving photocatalytic activity due to the synergistic effect [3, 4]. For the large-scale applications of such materials, their mass quantity is required. In this case, the fluoride processing of the most abundant natural mineral ilmenite (FeTiO3) with solid NH4HF2 (m. p. 126 oC) can be used. We have carefully studied this process [5]. Fluorination reactions of raw materials with NH4HF2 are thermodynamically possible and proceed exothermally (even at room temperature). Fluorination products are mainly nonstoichiometric phases of high symmetry: tetragonal double salts of silicon and titanium (NH4)3[Si(Ti)F6]F, cubic fluoroelpasolites and fluoroperovskites, which were isolated in a single crystal form and their crystal structures were determined (or refined). Their phase transitions at temperature decreasing, thermal and hydrolytic properties were studied. The compounds were investigated by X-ray diffraction, differential thermal analysis (DTA), differential scanning microcalorimetry (DSM) and adiabatic calorimetry, NMR, infrared, Raman, XPS, and Mössbauer spectroscopies. The tensimetry method was also used for establishment of incongruent sublimation of (NH4)2SiF6. [1] H.K. Lee, S.W. Lee, Chem. Lett. 44 (2015) 604-606. |
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