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Pristine Simple Oxides as Visible Light Driven Photocatalysts: Highly Efficient
Decomposition of Organic Compounds over Platinum-loaded Tungsten Oxide
Ryu Abe,*,†,§ Hitoshi Takami,§ Naoya Murakami,§ and Bunsho Ohtani†
Catalysis Research Center, Hokkaido University, Sapporo 001-0021, Japan
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan
RECEIVED DATE (automatically inserted by publisher); E-mail: ryu-abe@cat.hokudai.ac.jp
a) Preparation of Pt-loaded WO3 photocatalysts
Fine particulate WO3 with a particle size of 50–200 nm was separated from commercial WO3 powder (99.99%, Kojundo Chemical
Laboratory Co.) as follows. The WO3 powder (5 g) was suspended in purified water (100 mL) with ultrasonic irradiation for 30 min, and
then the suspension was centrifuged at 1000 rpm for 10 min. After the removal of precipitate containing large aggregates, fine particulate
WO3 with a particle size of 50–200 nm was collected by centrifugation (10000 rpm for 30 min). BET specific surface area of obtained
WO3 fine particles, which was determined by nitrogen-adsorption at 77 K, was ca. 10.5 m2g–1. (before the separation: ca. 2.4 m2g–1)
Platinum-loaded WO3 samples (Pt-WO3) were prepared as follows. An aqueous suspension containing the fine particulate WO3 and
hexachloroplatinic acid (H2PtCl6·6H2O) was exposed to visible light (λ > 400 nm) provided by a 300 W Xe lamp (LX-300F, Cermax)
fitted with a cutoff filter (L-42, HOYA). After 2 h of irradiation, methanol (10 vol%) was added and the suspension exposed to further
irradiation for 2 h. This procedure resulted in a highly uniform dispersion of
platinum particles (average size, 5 nm) on the WO3 surface, as shown in Fig.
S1. Titanium (IV) oxide (TiO2 P25, Nippon Aerosil, Japan, ca. 55.4 m2g–1)
was used as a reference photocatalyst. Nitrogen-doped TiO2 (N-TiO2) for
comparative analysis was prepared by treatment of TiO2 powder (ST-01,
Ishihara Sangyo Kaisha Ltd., ca. 320 m2g–1) under NH3 flow (50 mL min–1) at
823 K for 3 h. This method is known as relatively reproducible procedure to
prepare active N-TiO2 sample, and applied in a considerable number of
studies. We confirmed that the visible-light induced activities of prepared N-
TiO2 sample were comparable to those reported in the literatures. The specific
surface area of N-TiO2 sample was determined to be ca. 88.9 m2g–1.
Figure S1 Scanning transmission microscopy images of
Pt(1 wt%)-WO3 samples.
b) Photoreactivity Experiments
Photocatalytic decomposition of acetic acid (AcOH) was carried out in a Pyrex reaction cell containing a suspension of the photocatalyst
powder (50 mg) in an aerated aqueous AcOH solution (5 vol%, 250 mL) with continuous agitation using a magnetic stirrer. Photocatalytic
decomposition of acetaldehyde (AcH) or isopropyl alcohol (IPA) was performed using a Pyrex reaction cell with internal volume of
330 mL. The photocatalyst powder (50 mg) was spread in a square (15×15 mm) on the bottom of the reactor, and gaseous AcH (1000 ppm,
ca. 15 µmol) or IPA (1200 ppm, ca. 17 µmol) was introduced into the cell. In both cases, a 300 W Xe lamp was used as the light source.
Components in the gas phase were analyzed by gas chromatography. Action spectrum analysis for AcOH decomposition was performed
under monochromatic irradiation. In this case, 10 mg of photocatalyst powder was suspended in an aerated aqueous AcOH solution
(5 vol%, 2 mL), which was subjected to monochromatic irradiation (with FWHM ~17 nm) in the range of 300-600 nm using a diffraction
grating type illuminator (Jasco CRM-FD) equipped with a 300-W xenon lamp (Hamamatsu Photonics C2578-02). The intensity of
–
irradiation, measured by a Molectron PM5200 laser power meter, was in the range of 1.98-6.52 10–8 einstein s .
1
1
c) Photoacoustic Spectroscopic Measurements
Photoacoustic spectroscopic measurements were conducted using a home-made PA cell
0.8
composed of an aluminum body (internal volume, ca. 1 mL) with a Pyrex window and
two valves for gas flow. Three atmospheres were used in the reactions: flows of ambient
0.6
UV-irradiation
air, nitrogen (N2), or O2 containing isopropyl alcohol (IPA) vapor. Monochromatic light
0.4
(ca. 0.2 mW cm−2) chopped at 80 Hz was obtained from a Xe lamp as modulated probe
light, and an ultraviolet light-emitting diode (365 nm, ca. 2.8 mW cm−2) was employed as
0.2
continuous irradiation for excitation of WO3. The PA signal was acquired by a condenser
microphone buried in the cell, and amplified and monitored using a digital lock-in
0
400
450
500
550
600
650
700
amplifier. In time-resolved analyses, a light-emitting diode (625 nm) was used as a probe
light, and the output intensity was modulated by a digital function generator at 80 Hz. The
PA spectrum of bare WO3 under UV irradiation in the presence of air and IPA vapor
exhibits an upward shift in the visible region at wavelengths longer than 470 nm, as shown
in Fig. S2.
Wavelength / nm
Figure S2 Photoacoustic spectra of a bare WO3
powder before (open symbols) and after (closed
symbols) UV irradiation for 30 min in air
containing IPA vapor
Abe, Ryu
