Preparation of TiO2 photocatalysts by multi-gelation and their photocatalytic reactivity for the degradation of 2-propanol

Article abstract of DOI:10.1246/cl.2004.268

TiO₂ photocatalysts, prepared by a multi-gelation method, showed higher photocatalytic activity for the degradation of 2-propanol diluted in water. This multi-gelation method showed a good performance in controlling the parameters viz. particle size, surface area, crystallinity as well as anatase and rutile phase composition, which are responsible for the higher activity of these photocatalysts.

Full text of DOI:10.1246/cl.2004.268

268
Chemistry Letters Vol.33, No.3 (2004)
Preparation of TiO2 Photocatalysts by Multi-gelation and Their Photocatalytic Reactivity
for the Degradation of 2-Propanol
Bernaurdshaw Neppolian, Hiromi Yamashita, Yoshimi Okada,y Hiroaki Nishijima,y and Masakazu Anpoꢀ
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University,
Gakuen-Cho 1-1, Sakai, Osaka 599-8531
yChiyoda Corporation, R&D Centre, Minamiwatarida-cho 1-1, Kawasaki-ku, Kawasaki, Kanagawa 210-0855
(Received November 5, 2003; CL-031059)
TiO2 photocatalysts, prepared by a multi-gelation method,
by a gas chromatograph.
showed higher photocatalytic activity for the degradation of 2-
propanol diluted in water. This multi-gelation method showed
a good performance in controlling the parameters viz. particle
size, surface area, crystallinity as well as anatase and rutile phase
composition, which are responsible for the higher activity of
these photocatalysts.
The oxidative degradation of 2-propanol proceeded as a
photocatalytic reaction on TiO2 prepared by the multi-gelation
method and produced acetone as the intermediate product as
well as CO2 and water as the final products under UV light irra-
diation. The catalysts prepared at 673 K (Cat-1 and Cat-2)
showed less photocatalytic activity during the reaction with 2-
propanol due to its amorphous nature (Figure 1). However, the
catalysts prepared at 773 K (Cat-3 and Cat-4) were more active
due to the formation of an anatase phase with a well-crystalline
structure. Since the anatase phase exhibits lower rates of recom-
bination of the photo-formed electrons and holes due to its high-
er rate of hole trapping11 and a higher surface adsorptive capaci-
ty,12 it is generally considered to be a photocatalytically active
phase of TiO2 for the degradation of organic compounds.8 How-
ever, the catalysts prepared at 823 K (Cat-5 and Cat-6) were
shown to be more highly active (Figure 1) not only for their
well-crystalline structure but also due to the varied composition
ratio of anatase and rutile as with P-25 (Degussa) (Table 1). Al-
though the anatase phase is considered to be more active, a com-
bination of rutile and anatase is favourable in enhancing the rate
of the degradation of organic pollutants.11,13
A variety of semiconductor photocatalysts have been devel-
oped in recent years to improve the selectivity and efficiency for
the photocatalytic degradation of organic pollutants.1–7 Among
the various photocatalysts, TiO2 has attracted a great deal of at-
tention because of its high photocatalytic activity, thermal stabil-
ity, and non-corrosive properties. It is well known that TiO2 has
three modification phases: anatase, rutile, and brookite, in which
anatase TiO2 is more active than the other two forms for the deg-
radation of organic compounds.8 It has been widely reported that
the photocatalytic activity of TiO2 differs depending on the prep-
aration and treatment conditions. In our recent studies, we have
prepared TiO2 photocatalysts by a multi-gelation method9,10 in
which variations in the pH values are applied. Photocatalysts
prepared by this method have a well-defined crystalline struc-
ture, uniform particle size, high surface area and more anatase
phase in comparison with other commercially available cata-
lysts. Since TiCl4 and ammonium solutions are added to the ves-
sel alternately and hydrous titanium oxide particles are formed
periodically with the dissolution of the smaller particles, the
multi-gelation method showed high performance in controlling
the particle size, surface area and crystallinity of the particles.
The TiCl4 solution was prepared by mixing equal weight of
TiCl4 (obtained from Wako chemicals, Japan) with crushed ice
made from distilled water. The TiO2 catalysts used were pre-
pared by continuous heating and stirring of the TiCl4 solution
(500 mL) with an aqueous ammonia solution (14 wt %,
710 mL) under different pH swings at 353 K. A white precipitate
of TiO2 was formed, filtered and dried at 393 K for 15 h. The
dried TiO2 was calcined at various temperatures with an electric
furnace under a flow of air. The UV–vis absorption spectra and
X-ray diffraction (XRD) patterns of the catalysts were then re-
corded and analyzed. The N2 BET surface area of the TiO2 cat-
alysts was also determined. The photocatalyst (50 mg) was trans-
ferred to a quartz cell with an aqueous solution of 2-propanol
(2:6 ꢁ 10ꢂ3 mol dmꢂ3, 25 mL). Prior to UV irradiation, the sus-
pension was stirred for 1 h under dark conditions. The sample
was then irradiated at 295 K using UV light (ꢀ > 250 nm) from
a 100-W high-pressure Hg lamp with continuous stirring under
oxygen atmosphere in the system. The products were analyzed
It is interesting to note that the pH swing has a strong influ-
ence on the degradation of 2-propanol, which is observed with
Cat-6 prepared after 7 times pH values swing (Figure 1). This
is due to the dissolution of smaller particles by the alternate ad-
dition of TiCl4 solution as an acidic reagent and ammonium hy-
droxide as a basic reagent. Similarly, the oxidation of 2-propanol
was carried out with catalysts prepared at 873 K calcination tem-
30
20
10
0
Cat-1
Cat-2
Cat-3
Cat-4
Catalysts
30
20
10
0
Cat-5
Cat-6
Cat-7
Cat-8
P-25
Catalysts
Figure 1. Oxidative degradation of 2-propanol with the differ-
ent photocatalysts atfer 1 hr irradiation.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.3 (2004)
269
Table 1. Characterization of the TiO2 photocatalysts prepared
by the multi-gelation method
It is clear from these results that the control of the pH swing
plays an important role in the phase transition leading to higher
photocatalytic activity.
From our experimental observations, it was confirmed that
TiO2 catalysts prepared by this unique multi-gelation method,
i.e., adopting variations in the pH swing, significantly showed
higher photocatalytic activity for the degradation of 2-propanol.
Further research is underway to improve the nature and photoca-
talytic properties of the prepared TiO2 photocatalysts.
Catalyst
Name
Cal.
temp.
/K
Number Surface Particle Anatase
: Rutile
of pH
swings
area
/m2/g
size
/nm
Cat-1
Cat-2
Cat-3
Cat-4
Cat-5
Cat-6
Cat-7
Cat-8
673
673
773
773
823
823
873
873
3
7
3
7
3
7
3
7
106
107
59
73
38
59
16
29
09.8
17.5
11.7
18.5
12.8
19.0
20.8
23.9
-
-
87:13
92:08
62:38
80:20
25:75
50:50
Japan Society for the Promotion of Science (JSPS) is grate-
fully acknowledged by B. N. for financial support.
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Cal. temp.: calcination temperature
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Published on the web (Advance View) February 2, 2004; DOI 10.1246/cl.2004.268