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Study of the anatase to rutile transformation kinetics of the modified TiO2

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Grzmil B., Gleń M., Kic B., Lubkowski K.
Polish Journal of Chemical Technology
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2013
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vol. 15
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issue 2
73-80
EN
TiO2 attracts much interest because of its many potential applications. The use of titanium dioxide strongly depends on its polymorphic form: brookite, anatase, or rutile. Only rutile and anatase play an important role in industry. Anatase as a metastable form undergoes a non-reversible transformation into rutile. Understanding the kinetics of phase transformation and the processes of crystal growth of a material is essential for controlling its structure and, thus, its specific properties. The main purpose of this paper is to explain the anatase to rutile recrystallization kinetics in the modified TiO2 calcined from industrial hydrated titanium dioxide. The apparent activation energy of anatase to rutile transformation and the average size of titanium dioxide crystallites were determined for the unmodified TiO2 and TiO2 modified with P, K, Al, B, Zn, Zr, Ce, Sn, or Sb introduced in the amount of 0.5 mol% and 1.0 mol% when recalculated for their oxides. The growth of TiO2 crystallites during calcination was strongly inhibited by P, Ce and Zr, and inhibited to a lesser degree by Al, Sn and Sb. B and Zn did not affect the investigated process and K accelerated crystallites growth. The values of apparent activation energy depending on a modifier formed a relationship: Al
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Activity of phthalocyanine-sensitized TiO2-anatase in photooxidation of sulfite ions

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Galbas M., Banaszczyk A., Dyrda G., Szczegot K., Słota R.
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EN
Hybrid catalysts based on the TiO2 matrix impregnated with Nd, Eu and Yb diphthalocyanines proved effective in oxidation of sulfite ions under irradiation with light from the UV-visible range. Micro- and nano-crystalline anatase powders were used in preparation of the photocatalysts, which were applied in the form of a suspension in the water phase. The reaction yield was found to depend on the phthalocyanine sensitizer used and the conditions of TiO2 impregnation. The best results were obtained when micro-anatase impregnated with Yb-diphthalocyanine was used.
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Effect of calcination temperature on photocatalytic activity of TiO2. Photodecomposition of mono- and polyazo dyes in water

86%
Mozia S.
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EN
The presented studies have focused on the influence of TiO2 properties, such as crystalline phase, crystallite size and surface area, on the effectiveness of degradation of azo dyes in water under UV irradiation. Two monoazo dyes: Acid Red 18 (AR18, C20H11N2Na3O10S3) and Acid Yellow 36 (AY36, C18H14N3NaO3S), and one polyazo dye Direct Green 99 (DG99, C44H28N12Na4O14S4) were applied as model compounds. The photocatalysts were prepared from a crude titanium dioxide obtained directly from the production line (sulfate technology) at the Chemical Factory "Police" (Poland). The crude TiO2 was calcinated in air for 1-4h at the temperatures ranging from 600 to 800°C. The BET specific surface area of TiO2 decreased gradually with increasing the calcination temperature. The crude TiO2 exhibited specific surface area of 277 m2/g. In case of the catalysts heated at 600, 700 and 800°C the BET surface area amounted to 62.3-53.3, 33.4-26.8 and 8.9-8.3 m2/g, for the calcination time of 1-4h, respectively. The crystallite size of anatase increased with increasing heat treatment temperature and ranged from 19 to 53 nm, for the temperatures of 600-800°C, respectively. The catalysts annealed at 600 and 700°C contained primarily anatase phase (94-97%), whereas the photocatalysts heated at 800°C were composed mainly of rutile (97-99%). The highest effectiveness of azo dyes degradation was obtained in case of the photocatalyst calcinated for 1h at 700°C. The photocatalyst was composed mainly of anatase (97%) with crystallite size of 27 nm. The most effectively photodegraded was AR18, having the molecular weight of 640.4 g/mol. The most difficult to degrade was AY36 exhibiting the lowest molecular weight from all the dyes used (375.4 g/mol).
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