Comparative study of phase transition and textural changes upon calcination of two commercial titania samples: A pure anatase and a mixed anatase-rutile

Journal Article · Tue Dec 15 00:00:00 EST 2015 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/J.JSSC.2015.08.040· OSTI ID:22573958

Kordouli, Eleana ^[1]; Dracopoulos, Vassileios ^[2]; Vaimakis, Tiverios ^[3]; Bourikas, Kyriakos ^[4]; Lycourghiotis, Alexis ^[1]; Kordulis, Christos ^[1]

---

1. Department of Chemistry, University of Patras, GR-26504 (Greece)
2. Foundation for Research and Technology, Institute of Chemical Engineering Sciences (FORTH/ICE-HT), Stadiou street Platani, GR-26504, Rion Patras (Greece)
3. Department of Chemistry, University of Ioannina, P.O. Box 1186, 45110 Ioannina (Greece)
4. School of Science and Technology, Hellenic Open University, GR-26222, Patras (Greece)

The effect of calcination temperature and time on structural and textural changes of two commercial TiO{sub 2} samples (pure anatase and a mixture of anatase and rutile) has been investigated using N{sub 2} physisorption, ex-situ and in-situ X-ray powder diffraction, differential scanning calorimetry and UV–vis diffuse reflectance spectroscopy. The increase of the calcination temperature (up to 700 °C) and time (up to 8 h) causes only textural changes in the pure anatase, whereas a transformation of the anatase to rutile takes place, in addition, in the mixed titania (containing anatase and rutile). The textural changes observed in pure anatase sample were attributed to solid state diffusion leading to an increase in the size of anatase nanocrystals, through sintering. Thus, the mean pore diameter shifts to higher values and the pore volume and specific surface area decrease. The successful application of the Johnson–Mehl–Avrami–Kolmogorov model in the kinetic data concerning the pure anatase indicates a mass transfer control of sintering process. Similar textural changes were also observed upon calcination of the sample containing anatase and rutile. In this case not only sintering but the anatase to rutile transformation contributes also to the textural changes. Kinetic analysis showed that the rutile nanocrystals in the mixed titania served as seed for by-passing the high energy barrier nucleation step allowing/facilitating thus the anatase to rutile transformation. A fine control of the anatase to rutile ratio and thus of energy-gap and the population of hetero-junctions may be obtained by adjusting the calcination temperature and time. - Graphical Abstract: Dependence of anatase content of P25 on the calcination temperature (600 °C (■), 650 °C (●), 700 °C (▲)) and time. - Highlights: • Increase of calcination temperature up to 800 °C and time up to 8 h causes only textural changes in pure anatase • Progressive transformation of anatase to rutile with time takes place in the mixed titania above 600 °C • A high activation energy barrier inhibits the solid state transformation in pure anatase • Rutile nanocrystals in mixed titania serve as seeding for favouring transformation • Calcination temperature and time allow a fine control of E{sub g} and heterojunctions population in mixed titania.

• OSTI ID: 22573958
• Journal Information: Journal of Solid State Chemistry, Vol. 232; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ACTIVATION ENERGY
CALCINATION
CALORIMETRY
MASS TRANSFER
MIXTURES
NANOPARTICLES
NANOSTRUCTURES
PHASE TRANSFORMATIONS
PHOSPHORUS 25
POWDERS
RUTILE
SINTERING
SOLIDS
SPECIFIC SURFACE AREA
SPECTROSCOPY
SURFACES
TITANIUM OXIDES
VENTILATION BARRIERS
X RADIATION
X-RAY DIFFRACTION