Journal of Colloid and Interface Science 302 (2006) 530–536
Solvothermal synthesis and characterization of anatase TiO2nanocrystals
with ultrahigh surface area
Rajeev K. Wahi, Yunping Liu∗, Joshua C. Falkner, Vicki L. Colvin∗
Chemistry Department, MS-60, Center for Biological and Environmental Nanotechnology, Rice University, Houston, TX 77005-1892, USA
Received 9 December 2005; accepted 5 July 2006
Available online 11 July 2006
Phase-pure, ultrafine nanocrystalline anatase with high specific surface area (up to 250 m2g−1) was obtained upon injection of a titanium
alkoxide precursor into ethanol with designed volume of water under mild solvothermal conditions (<200◦C, 2 h). Primary particle sizes were
tuned by adjusting various reaction parameters, with the smallest grain sizes occurring at low temperatures (140–150◦C), low initial alkoxide
concentrations, and intermediate hydrolysis ratios (r ≡[H2O]/[Ti(OR)4] = 5–10). Additionally, variations in the reaction temperature result in
changes in particle morphology and distribution, with high-temperature samples exhibiting bimodal distributions of small spherical and larger
cubic particles that suggest grain growth via Ostwald ripening. A crystalline product with high thermal stability and specific surface area up to
5 times that of commercial nano-titania can be obtained at a relatively low temperature of 150◦C. The physical properties of the titania samples
obtained in this study suggest they might be well suited for catalytic applications.
© 2006 Elsevier Inc. All rights reserved.
Keywords: Titanium dioxide; Nanocrystal; Anatase; Solvothermal synthesis; Characterization; Ultrahigh surface area
Nanocrystalline titanium dioxide (TiO2) has emerged as an
attractive multi-purpose material, its applications include in
photovoltaic solar cells, gas sensors [1,2], catalytic oxidation
of carbon monoxide and the photocatalytic decomposition of
organic environmental contaminants [3–9]. Its widespread ap-
plications make the preparation extensively studied [10–32]. In
recent years a wide variety of methods have been developed to
produce nano-titania with properties tailored to different appli-
cations, such as aerosol pyrolysis, sol–gel technique, calcina-
tion of amorphous titania, and surfactant-based colloidal syn-
thesis [10–17]. However, the products obtained in such synthe-
ses are usually inadequate for the purposes of catalytic applica-
tions, which require nanocrystalline titania consisting mostly or
entirely of fine-grained (<10 nm) anatase with extremely high
specific surface area (>200 m2g−1) [18–21]. They either pro-
duce large primary particles (>20 nm) with low specific surface
*Corresponding authors. Fax: +1 713 348 2578.
E-mail addresses: email@example.com (Y. Liu), firstname.lastname@example.org (V.L. Colvin).
areas surfactant molecules on particle surfaces prevents molec-
ular species from accessing the active surface sites, thereby
limiting the product’s efficacy as a catalyst [10–17].
A surfactant-free hydrothermal technique (i.e., high-temper-
ature, high-pressure) has been shown to be an suitable way for
obtaining titania with small grain sizes, high specific surface
areas, and high crystallinity [18,20–25]. In stead of aqueous
system, ethanol, an organic solvent was chosen for our study.
This solvothermal technique was recently introduced to synthe-
size some ceramic oxides [26–32], including nanocrystal TiO2
powders [28–32]. These studies showed it had not only the ad-
vantages of hydrothermal synthesis, but also avoided contami-
surface area and quality. It also makes it possible to probe the
effects of the water:alkoxide molar ratio in same phase. Despite
the advantages that solvothermal synthesis offers, however, it
did not widely explore the relations between synthetic parame-
ters and physical properties of the obtained particles, i.e., ratio
of precursors to water in homogeneous phase (ethanol+water),
and did not yields anatase with specific surface areas above
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R.K. Wahi et al. / Journal of Colloid and Interface Science 302 (2006) 530–536
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