Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 5, pp. 783−788.
Pleiades Publishing, Ltd., 2009.
Original Russian Text
K.L. Vasil’eva, O.M. Ishchenko, N.V. Zakharova, A.A. Malkov, A.A. Malygin, 2009, published in Zhurnal Prikladnoi Khimii, 2009,
Vol. 82, No. 5, pp. 731−736.
OF SYSTEMS AND PROCESSES
A Study of Phase Transformations in the Surface Layer
of Titanium Dioxide
K. L. Vasil’eva, O. M. Ishchenko, N. V. Zakharova, A. A. Malkov, and A. A. Malygin
St. Petersburg Technological Institute, St. Petersburg, Russia
Received November 5, 2008
Abstract—The capabilities of the diffuse reflectance spectroscopy in a study of the state of the surface layer of
anatase in anatase–rutile phase transformations in successive thermal treatments of anatase in the temperature
range 200–900°C and in analysis of titanium dioxide of P25 brand (Degussa) containing anatase and rutile in
a 80 : 20 ratio, respectively, are demonstrated for the example of dispersed titanium oxide.
It is known that the composition, structure, and
properties of solids predetermine their possible
transformations in various technological processes .
An important factor determining the sorption, catalytic,
and other properties of solids is their phase composition.
In view of the important role of the surface in these
materials, it is important to control not only the structure
of the bulk phase, but also that of the surface layer
to a depth of several tens of nanometers. However,
as a rule, information about the phase composition
traditionally refers to the bulk of solids and contains no
data on the structure of their surface layers. At the same
time, it is known that, for example, structural-phase
transformations occur in the surface layer under thermal
treatment at considerably lower temperatures, compared
with transformations in the bulk .
A characteristic example is titanium dioxide. Owing
to its chemical stability in acid and neutral liquid media,
electrical conductivity, and photocatalytic activity, this
compound is widely used in manufacture of ﬁ llers for
composite polymeric materials, dielectric ceramics,
ceramic films, and pigments for paint-and-varnish
industry; in electronic devices, photoelectrochemical
cells, photocatalysis, chemical sensors, solar cells, etc. [2,
3]. Depending on the crystalline modiﬁ cation, titanium
dioxide (anatase, rutile, and brookite) exhibits different
physicochemical properties. In the simultaneous presence
of amorphous, anatase, and rutile constituents, the
titanium oxide material has an increased photocatalytic
activity, compared with a material composed of only
a single crystallographic phase .
It is known that the formation of a TiO
is strongly affected by the mode of its thermal treatment,
during which a phase transition in a solid begins with the
lattice rearrangement in the surface layer at substantially
lower temperatures . For example, in calcination of
amorphous titanium(IV) hydroxide at low temperatures
(500–550°C), nanocrystalline anatase particles are
originally formed. Further increase in temperature and
treatment duration results in that rutile crystallites appear
and the anatase–rutile phase transition occurs . At the
same time, the phase transition in titanium dioxide begins
at the surface at a lower temperature, compared with the
bulk , and can be characterized by a change in the
composition of functional groups and in the total surface
energy. In , the surface of titanium dioxide samples
was studied by the potentiometric method. In this case,
a transition from one phase state to another as a result of
thermal treatment can be characterized by a change in the
composition of adsorption centers and by the conditional
adsorption potential for iron(III) ions.
Together with the method used in , there exist
other ways to study the surface state of solids. These
techniques are based, in particular, on adsorption of acid-
base indicators  and probe molecules [7, 8], followed
by identiﬁ cation by electronic and IR spectroscopies [9,
10, 11], pH measurements [12, 13], and ESR spectroscopy
. However, all these methods used for analyzing