Microstructural evolution of metallorganic derived
Pt-doped TiO2
Issei Hayakawaa) and Yuji Iwamotob)
Fine Ceramics Research Association, Synergy Ceramics Laboratory, 2-4-1, Mutsuno, Atsutaku,
Nagoya, 456-8587, Japan
Ko-ichi Kikuta and Shin-ichi Hirano
Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan
(Received 26 October 1999; accepted 12 September 2000)
A metalorganic precursor containing Ti and Pt was synthesized using Ti alkoxide
derivative, amino acid, and platinum salt. The decomposition behavior of the precursor
and thin-film formation were examined in terms of microstructure evolution and
crystallization. The precursor yielded anatase at 400 °C. Grain growth of platinum
particles and TiO2 grains was suppressed even at 800 °C in the films. Suppression of
grain growth was attributed to an effect of film thickness.
such a precursor. Such a highly dispersed state can con-
I. INTRODUCTION
tribute to the formation of very fine Pt particles and high
dispersion of Pt after heating.
TiO2-based materials have received attention because
of their heat resistance, chemical stability, semiconduct-
ing properties, and photosensitive properties. Therefore,
this material has been used for sensors,1–5 catalysts,6,7
and electrodes.8 As a catalyst, it is known that the addi-
tion of noble metal to metal oxide enhances the catalytic
property.9 In this case, the decrease of particle size of the
noble metal is effective for the improvement of the cata-
lytic properties. This is due to the increased number of
active sites and the enhancement of surface activity.
Moreover, the catalytic properties of TiO2-based materi-
als containing noble metal depend on microstructure, the
grain size of the matrix, the dispersion of noble metal,
and pore structure.
TiO2 powders dispersed with Pt are usually synthe-
sized using TiO2 fine powders or TiO2 sol with Pt
salt.10,11 In the former, fine Pt particles of 1.5–4.0 nm in
diameter are formed on the surface of TiO2 grains by
heating at 480 °C in H2. However, it is not well known
how Pt particles are dispersed in TiO2 matrix. This is
because catalytic activity considerably decreases due to
the decrease of surface area resulting from densification
of TiO2 grains.
Microstructure derived from metalorganic precursor
depends on the chemical composition and molecular
structure of the precursor, heating temperature, and heat-
ing atmosphere. This paper describes the microstructure
changes from precursors containing titanium and plati-
num through heating to form powders and thin films.
II. EXPERIMENTAL
Figure 1 is a flow chart showing the synthesis of the
precursor solution containing Ti and Pt. A 75% isopro-
panol solution of Ti(O–iPr)2(AcAc)2 (Nisso, T-50, Ja-
pan) was used as a Ti source to prepare the precursor
solution containing Ti and Pt. Amino acid (L-lysine)
is barely soluble in isopropanol, but better dissolved
in methanol. Therefore, L-lysine of 7.72 × 10−4 mol
was dissolved in methanol. Methanol was added to
T-50 containing Ti(O–iPr)2(AcAc)2 of 1.78 × 10−2 mol.
These solutions were mixed and reacted at 75 °C.
H2PtCl6 и 6H2O of 1.45 × 10−4 mol was then dissolved in
methanol and added to this reacted solution. This mixed
solution was refluxed at 75 °C. The amino acid reacted
with an alkoxy group of Ti(O–iPr)2(AcAc)2 and with
platinum ions. Next, an excess amount of water of
0.55 mol was added to hydrolyze the residual alkoxy
groups of Ti(O–iPr)2(AcAc)2. If a large excess L-lysine
is used, two O–iPr groups of Ti(O–iPr)2(AcAc)2 react
with L-lysine. Hence, hydrolyzable O–iPr groups are lost
and the formation of partially hydrolyzed molecules such
as R–[Ti(AcAc)2–O]n–RЈ are hindered when water of
Metalorganic precursor processes are found to be very
effective for controlling microstructure on the nanoscale
because each element in the precursor is bonded and
homogeneously dispersed at an atomic level. Pt remains
in the Ti–O network even after precipitation by using
a)Present address: Material Research Laboratory, Corporate Tech-
nical Center, NGK Insulators, Ltd., Nagoya, Japan.
b)Present address: Japan Fine Ceramics Center, Nagoya, Japan.
2794
J. Mater. Res., Vol. 15, No. 12, Dec 2000
© 2000 Materials Research Society
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