J. Am. Ceram. Soc., 85 [2] 341–45 (2002)
journal
Photocatalytic Characteristics of Nanometer-Sized Titania Powders
Fabricated by a Homogeneous-Precipitation Process
Kang Ryeol Lee,† Sun Jae Kim,‡ Jae Sung Song,§ Ju Hyeon Lee,¶
Yun Joong Chung,† and Sung Park†
Department of Ceramic Engineering, Myongji University, Kyunggido, 449–728, Korea
Department of Advanced Materials Engineering, Sejong University, Seoul 143–747, Korea
Korea Electrotechnology Research Institute, Changwon 641–120, Korea
Department of Materials Science and Engineering, Sunmoon University, Asan, 336–840, Korea
The photocatalytic characteristics of nanometer-sized TiO2
powder prepared by a homogeneous-precipitation process
(HPP) were compared with those of a commercial powder to
determine which powder was better able to remove metal ions,
such as lead and copper, from aqueous equimolar metal-
ethylenediaminetetraacetic acid (EDTA) solution. In aqueous
lead-EDTA solution, the TiO2 powder fabricated by HPP had
3.5 times higher initial adsorption of lead ion and a 1.5 times
faster rate for the complete elimination of lead ions than did
the commercial powder. In an aqueous copper-EDTA solution,
the TiO2 powder fabricated by HPP also showed higher initial
adsorption and a faster elimination rate for copper ions than
did the commercial powder. Similarly, the photocatalytic
properties were enhanced as the specific surface area in-
creased, and the TiO2 powder fabricated by HPP, which
consisted of coagulated primary particles 20 nm in size, with
chestnut-burr shapes, had a larger specific surface area
(ϳ180 m2/g) than that of the commercial powder (ϳ55 m2/g).
process, leading to low quality in the final TiO2 powder. For the
chloride process, TiCl4 is produced by reacting natural rutile ore
with HCl gas at high temperature; TiO2 powder with a high-purity
rutile structure (Ͼ99.9%) then is obtained by the TiCl4 with
oxygen gas at Ͼ1000°C. The TiO2 powder fabricated by the
chloride method is fine sized but rough shaped. Furthermore, the
chloride process requires supplementary protection devices be-
cause of the corrosiveness of the HCl or Cl2 gas, resulting in higher
production costs.
The application for TiO2 powder obtained by these methods is
limited, because the particle shape, size, and distribution cannot be
controlled during the processes. Thus, recent studies have exam-
ined better means of controlling powder characteristics, such as the
solϪgel method12,13 and hydrothermal synthesis.1,14 The metal–
alkoxide process usually is used to fabricate spherical TiO2
powders of uniform size on a laboratory scale. This solϪgel
method using alkoxide produces fine, spherical powders of uni-
form size, Ͻ1.0 m. However, tight control of reaction conditions
is required, because alkoxides hydrolyze intensely in air. Further-
more, the high price of alkoxides limits their commercialization
potential.
I. Introduction
Hydrothermal synthesis, using an autoclave under high temper-
ature and pressure, produces high-quality powders, but a continu-
ous process is impossible under this method. Therefore, a powder-
fabrication method that provides both easy control of powder
characteristics and ease of fabrication must be developed.
Many researchers have examined the photocatalytic properties
of TiO2 powder. Somorjai15 has suggested that photocatalytic
efficiency is lower in the rutile TiO2 phase, because recombination
of the electron–hole pairs produced by ultraviolet irradiation
occurs more rapidly on the surface of the rutile phase, and fewer
reactants and hydroxides are attached to the rutile than to the
anatase TiO2 phase. However, according to Mills et al.,16 the
decrease in the photocatalytic effect during transformation from
the anatase to the rutile TiO2 phase results from changes in the
specific surface area and porosity, rather than in the crystalline
structure. Also, Serpone17 has reported that light scattering is
higher for submicrometer-sized secondary particles of TiO2 than
nanoparticles when both of them have the same surface area. This
low light scattering of nanoparticles may yield superior efficiency
in photocatalysis.
ITANIA (TiO2) with rutile phase has been widely used for white
paint materials because of its good scattering abilities, which
T
protects surfaces from light. TiO2 also has been used for optical
coatings, beam splitters, and antireflection coatings because of its
high dielectric constant and refractive index, good adsorption of
oils, good tinting power, and good chemical stability, even under
strong acidic or basic ambient conditions.1–3 The electrical char-
acteristics of TiO2 differ with changes in the oxygen partial
pressure, because TiO2 has a wide, chemically stable and nonstoi-
chiometric phase region. Therefore, TiO2 also can be used for
humidity sensors and high-temperature oxygen sensors.4 TiO2
with an anatase structure is used as a photocatalyst for photo-
decomposition and solar-energy conversion because of its high
photoactivity.5–7 For the use of TiO2 as a photocatalyst, a higher
purity and larger specific surface area are imperative.
TiO2 for use as a photocatalyst is fabricated by either a sulfate
or a chloride process.8–11 For the sulfate process, ilmenite dis-
solved in H2SO4 is hydrolyzed at Ͼ95°C then calcined at
800°Ϫ1000°C and pulverized, to produce the TiO2 powder.
Impurities are introduced during this calcination and pulverization
In the present study, a nanostructured TiO2 rutile-phase powder
with
a large specific surface area was produced by a
homogeneous-precipitation process at ambient or very low tem-
peratures, Ͻ105°C (HPPLT),18,19 proposed to be a cost-effective
and high-quality process. The photocatalytic results for an HPPLT-
fabricated TiO2 powder were compared with those for a commer-
cially used powder (P-25, Degussa AS, Frankfort, Germany),
consisting mainly of the anatase phase, for the removal of
heavy-metal ions, such as lead and copper, from an aqueous
solution, and the reason for the superior photocatalytic efficiency
of the HPPLT-fabricated TiO2 powder was investigated.
T. M. Besmann—contributing editor
Manuscript No. 188151. Received November 10, 2000; approved October 22,
2001.
†Myongji University.
‡Sejong University.
§Korea Electrotechnology Research Institute.
¶Sunmoon University.
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