Photocatalytic Degradation of Gaseous Acetaldehyde over Rh-doped SrTiO3 under Visible Light Irradiation

Article abstract of DOI:10.1246/cl.150907

Rh-doped SrTiO₃ (STO:Rh), a visible-light-driven photocatalyst, was examined for the degradation of acetaldehyde as a volatile organic compound under visible light irradiation. Pristine STO:Rh showed slow degradation of acetaldehyde. After ball milling, the ground STO:Rh had a higher specific surface area than before ball milling, and demonstrated a higher degradation rate for acetaldehyde.

Full text of DOI:10.1246/cl.150907

CL-150907
Received: September 29, 2015 | Accepted: October 28, 2015 | Web Released: January 5, 2016
Photocatalytic Degradation of Gaseous Acetaldehyde over Rh-doped SrTiO3
under Visible Light Irradiation
Yuichi Yamaguchi,1,2 Chiaki Terashima,1 Hideki Sakai,1,2 Akira Fujishima,1 Akihiko Kudo,1,3 and Kazuya Nakata*1,4
1Research Institute for Science and Technology, Photocatalysis International Research Center,
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510
2Department of Pure and Applied Chemistry, Faculty of Science and Technology,
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510
3Department of Applied Chemistry, Faculty of Science, Tokyo University of Science,
1-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601
4Department of Applied Biological Science, Faculty of Science and Technology,
Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510
(E-mail: nakata@rs.tus.ac.jp)
Rh-doped SrTiO3 (STO:Rh), a visible-light-driven photo-
catalyst, was examined for the degradation of acetaldehyde as
a volatile organic compound under visible light irradiation.
Pristine STO:Rh showed slow degradation of acetaldehyde.
After ball milling, the ground STO:Rh had a higher specific
surface area than before ball milling, and demonstrated a higher
degradation rate for acetaldehyde.
(1.0 g) was transferred into a 45 mL container with 5.0 mL of
ultrapure water and 10 g of zirconia balls (diameter = 1.0 mm).
The powder was then milled twice at 800 rpm for 30 min in a
ball-milling device (Fritsch: Pulverisette 7). Finally, the ground
particles were collected by filtration, washed with ultrapure
water, and dried at 60 °C.
The photocatalytic oxidative decomposition of acetaldehyde
was examined as follows. A glass petri dish was covered
with 0.5 g of STO:Rh in a 500 mL closed glass reactor. The
¹2
Photocatalytic reactions under light irradiation have gained
much attention not only for water splitting for hydrogen fuel
production, but also for air and water cleaning.1-8 TiO2 is a
material that performs photocatalytic reactions under ultraviolet
(UV) light irradiation. However, only 3% of the solar spectrum
is composed of UV light. In order to accelerate photocatalytic
reactions, the whole range of solar light including visible (vis)
should be accessed. Therefore, it is important to develop
materials that respond to visible light, comprising 42% of
sunlight. Many visible-light-driven photocatalysts have been
developed, such as Bi2WO6, Bi2MoO6, Ag3VO4, and BiVO4,
which have demonstrated oxygen evolution from water.9-14
Recently, one of the authors reported a unique p-type photo-
catalyst, rhodium-doped SrTiO3 (STO:Rh), that was active
for hydrogen evolution from water under visible light irradi-
ation.15,16 In addition, BiVO4/STO:Rh composites and photo-
electrochemical cells can accomplish water splitting without an
external bias under visible light irradiation.17,18 Thus, STO:Rh
is available for water splitting as a visible-light-driven photo-
catalyst. The STO:Rh photocatalyst is also active for some
organic syntheses such as dehydrogenation of primary alco-
hols.19 However, there have been no reports on the capability of
STO:Rh for decomposing organic compounds for environmental
purification.
photocatalyst was irradiated at 100 mW cm light intensity
through an L-42 cutoff filter (- < 420 nm) using a 200 W Xe
lamp. The initial concentration of acetaldehyde was adjusted
at 85 ppm. The concentrations of acetaldehyde and carbon
dioxide were measured using a gas chromatograph with a flame
ionization detector equipped with a methanizer. Acetic acid was
detected using high-performance liquid chromatography.
In the X-ray diffraction (XRD) patterns for pristine and
ground STO:Rh (Figure 1), peaks of the pristine STO:Rh were
assigned to cubic SrTiO3. After grinding, the crystal phase of
STO:Rh was not changed while the full width at half-maximum
of the peaks was broadened because the crystalline size was
decreased by the ball-milling process.
In this work, we evaluate the degradation of acetaldehyde, a
voltaic organic compound recognized as an origin of the sick
building syndrome, using STO:Rh under visible light irradi-
ation. Furthermore, we examined the effect of grinding STO:Rh
by ball milling on its activity for acetaldehyde degradation.
STO:Rh was synthesized by a solid-state reaction.15
A
mixture of 17.1 mmol SrCO3 (Kanto Chemical), 15.8 mmol TiO2
(Soekawa Chemical Co.), and 0.08 mmol Rh2O3 (Wako Pure
Chemical) were ground in an alumina crucible with the addition
of a small amount of methanol. The mixture was calcined in air
at 1173 K for 1 h, then at 1373 K for 10 h. The resulting powder
Figure 1. XRD patterns of (A) pristine and (B) STO:Rh grounded
for 60 min.
42 | Chem. Lett. 2016, 45, 42–44 | doi:10.1246/cl.150907
© 2016 The Chemical Society of Japan

(A)
(B)
(A)
(B)
1 μm
(C)
400
500
600
700
800
Wavelength / nm
Figure 3. Diffuse reflectance spectra of (A) pristine, (B) STO:Rh
grounded for 60 min, and (C) STO:Rh grounded for 30 min.
100
dark
light
80
60
40
20
0
(A)
1 μm
(C)
(B)
(C)
-2
-1
0
1
2
3
4
Irradiation time / h
Figure 4. Photocatalytic degradation of acetaldehyde on (A) pris-
tine, (B) STO:Rh grounded for 30 min, and (C) STO:Rh grounded for
60 min under visible light irradiation (- > 420 nm). Photocatalyst:
0.5 g, light source: 200 W Xe lamp with L-42 cutoff filter, gas phase
volume: 500 mL.
1 μm
Figure 2. FE-SEM images of (A) pristine, (B) STO:Rh grounded for
30 min, and (C) STO:Rh grounded for 60 min.
Diffuse reflectance spectra for pristine and ground STO:Rh
showed a broad absorption band around 580 nm, attributed to
excitation from the valence band to the Rh4+ acceptor level
(Figure 3). The absorption around 580 nm decreased after ball
milling, possibly due to the reduction of Rh4+ to Rh3+ induced
by oxygen defects during ball milling to compensate the charge
valance. It was suggested with XPS (Figure S1).20-23
We examined the photocatalytic degradation of acetalde-
hyde by pristine and ground STO:Rh under visible light
irradiation (>420 nm), as shown in Figure 4. After equilibrium
in the dark for 2 h, the samples were illuminated by visible light
(100 mW cm¹2) through an L-42 (HOYA: <420 nm) filter from
Figure 2 shows field emission scanning electron microscope
(FE-SEM) images for pristine and ground STO:Rh. We
estimated the specific surface area from nitrogen adsorption at
77 K, using the Brunauer-Emmett-Teller formula. The small
specific surface area (2.6 m2 g¹1) and the large particle size (3-
5 ¯m) for pristine STO:Rh were due to sintering during high
temperature calcination. After ball milling for 30 and 60 min,
¹1
the surface areas increased significantly to 24 and 46 m2 g
,
respectively, while the particle size decreased to 100-500 nm.
Chem. Lett. 2016, 45, 42–44 | doi:10.1246/cl.150907
© 2016 The Chemical Society of Japan | 43

100
80
60
40
20
0
of acetic acid is possibly due to the stabilization of acetic acid on
the basic surface of STO:Rh and/or the insufficient oxidation
potential of holes for complete oxidation to CO2.25
In conclusion, STO:Rh prepared by a solid-state reaction
was ball milled to increase the specific surface area. Although
the concentration of acetaldehyde was slightly decreased using
pristine STO:Rh under visible light irradiation, it drastically
decreased for ground STO:Rh due to the high specific surface
area. Ground STO:Rh showed efficient degradation of acet-
aldehyde, a volatile organic compound, under visible light
irradiation.
This research was partially supported by the Strategic
International Research Cooperative Program, Japan Science and
Technology Agency (JST).
0
5
10
15
20
Supporting Information is available on http://dx.doi.org/
10.1246/cl.150907.
Irradiation time / h
Figure 5. Photocatalytic degradation of acetaldehyde on ground
STO:Rh under visible light irradiation (- > 420 nm). Photocatalyst:
0.5 g, light source: 200 W Xe lamp with L-42 cutoff filter, gas phase
volume: 500 mL.
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44 | Chem. Lett. 2016, 45, 42–44 | doi:10.1246/cl.150907
© 2016 The Chemical Society of Japan