1
Supporting information
Synergetic promotion of photocatalytic activity of TiO2 by gold
deposition under UV-visible light irradiation
Junqing Yan, Guangjun Wu, Naijia Guan and Landong Li*
Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of
Chemistry, Nankai University, Tianjin 300071, P.R. China
* Corresponding E-mail: [email protected]
Experiments and Methods
Preparation of TiO2 and Au/TiO2
All of the chemical reagents of analytical grade were purchased from Alfa Aesar
Chemical Co. and used as received without further purification.
In a typical synthesis of anatase TiO2, titanium tetrachloride (TiCl4) was dropwise
added into ice water under stirring to prepare a TiCl4 aqueous solution with
concentration of 1 mol/L. Then, 30 mL of TiCl4 aqueous solution was mixed with 30
mL 1 mol/L KOH, and the resulting solution was transferred into a 75 mL
Teflon-lined autoclave for static crystallization at 100 oC for 24 h. The obtained white
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solid was centrifuged and thoroughly washed with deionized water, followed by
drying in air at 80 oC for 24 h and calcination in a muffle furnace at temperatures of
400-700 oC for 12 h. The final products are denoted as TiO2-n, where n represents the
calcination temperature in centigrade.
Au clusters were loaded on the surface of TiO2 through so called photo-deposition
method. In a typical process, a certain amount of HAuCl4 solution, 500 mg of TiO2
and 10 mL of methanol were added into a round-bottom quartz flask under vigorous
stirring to form slurry. The pH value of the slurry was adjusted to 10.5±0.2 using
either 1M HCl or 1M NaOH aqueous solution and the slurry was irradiated by 250 W
high-pressure mercury light with the main wavelength of 365 nm for 6 h under the
protection of Ar. After irradiation, the solid particles were filtered, thoroughly washed
and dried at ambient conditions.
Characterization of Au/TiO2 samples
The specific surface areas of samples were determined through N2
adsorption/desorption isotherms at 77 K collected on a Quantachrome iQ-MP gas
adsorption analyzer.
The X-ray diffraction (XRD) patterns of samples were recorded on a Bruker D8
ADVANCE powder diffractometer using Cu-Kα radiation (λ= 0.1542 nm) at a
scanning rate of 4 o/min in the region of 2θ = 20-80o.
Transmission electron microscopy (TEM) images were taken on a Philips Tecnai
G2 20 S-TWIN electron microscope at an acceleration voltage of 200 kV. A few drops
of alcohol suspension containing the sample were placed on a carbon-coated copper
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grid, followed by evaporation at ambient temperature.
Light absorption spectra of samples (ca. 100 mg) were recorded in the air against
BaSO4 in the region of 200-700 nm on a Varian Cary 300 UV-Vis spectrophotometer.
X-ray photoelectron spectra (XPS) were recorded on a Kratos Axis Ultra DLD
spectrometer with a monochromated Al-Ka X-ray source (hv = 1486.6 eV), hybrid
(magnetic/electrostatic) optics and a multi-channel plate and delay line detector
(DLD). All spectra were recorded using an aperture slot of 300*700 microns, survey
spectra were recorded with a pass energy of 160 eV and high-resolution spectra with a
pass energy of 40 eV. Accurate binding energies (±0.1 eV) were determined with
respect to the position of the adventitious C 1s peak at 284.8 eV.
Electron spin resonance (ESR) was carried out on a Bruker A300 instrument with a
microwave power of 5.0 mW and a modulation frequency of 100 kHz.
2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) was used as an internal standard for
the measurement of the magnetic field. In a typical experiment, sample of 0.15g was
placed in a quartz ESR tube and evacuated at 473 K for 2 h. After cooled down to 298
K, 50 Torr O2 was introduced to the cube and kept for 15 min. The excess amount of
O2 was removed from the tube by evacuation for 10 min and then the tube was
analyzed at 100 K. The control experiments were carried out without O2 treatment.
All treatments were done in dark.
The photocatalytic generation of OH radicals under irradiation was measured by
the fluorescence method using the terephthalic acid (TA) as a chemical trap
( · OH + terephthalic acid → 2-hydroxyterephthalic acid ). Typically, 0.01g
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photocatalysts was dispersed in 50 mL aqueous solution containing 5x10-4 M
terephthalic acid, 2x10-3 M NaOH at 298 K and irradiated under UV, visible and
UV-visible light. Fluorescence emission intensity of generated 2-hydroxyterephthalic
acid at about 425 nm was measured on a Hitachi F-4500 fluorescence
spectrophotometer every 15 min under the excitation at 320 nm.
Photocatalytic evaluation
Photocatalytic reforming of methanol (also-known as photocatalytic water splitting
with methanol as sacrificial agent) was performed in a top-irradiation-type Pyrex
reaction cell connected to a closed gas circulation and evacuation system under the
irradiation of Xe lamp (wavelength: 320-780 nm) with different optical filters. In a
typical experiment, catalyst sample of 100 mg was suspended in 100 mL 10 %
methanol aqueous solution in the reaction cell. After evacuated for 30 min, the reactor
cell was irradiated by the Xe lamp at 200 W under stirring. The gaseous products were
analyzed by an on-line gas chromatograph (Varian CP-3800) with thermal
conductivity detector.
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Figures and Tables
Figure S1 XRD patterns and Raman spectra of Au/TiO2 samples
20 30 40 50 60 70 80
38.1
77.6
64.6
Inte
nsity
/ a.
u.
2 Theta / degree
Au/TiO2-700
Au/TiO2-600
Au/TiO2-500
Au/TiO2-400
44.3
200 400 600 800
200
Raman shift / cm-1
Inte
nsity
/ a.
u.EgA1gB1g
145
395 515 635
Eg
Au/TiO2-700
Au/TiO2-600
Au/TiO2-500
Au/TiO2-400
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Figure S2 ESR results of the Au/TiO2 and TiO2 samples
The samples were evacuated at 473 K and then treated with 50 Torr O2 at 298 K. The
samples were measured at 100 K in dark.
As shown in Figure S2, all anatase TiO2 samples show two signals, at g=2.00 and
g=2.03, which could be assigned to O– formed through O2 dissociative adsorption
onto the surface oxygen vacancy sites of TiO2, i.e. so-called surface defects [S1-S4].
Without O2 pretreatment, no ESR signals could be detected for all samples,
confirming that the signals are from the O–. After surface area normalization, the
intensity of ESR signals can reflect amount of defects per surface area, i.e. the density
of surface defects. The ESR signals decline dramatically with the loading of Au
1000 2000 3000 4000 5000 6000 7000
g = 2.00
TiO2-700
TiO2-600
TiO2-500
Au/TiO2-700
Au/TiO2-600
Au/TiO2-500
TiO2-400
g = 2.03
Au/TiO2-400No
rmal
ized
Inte
nsity
/ a.
u.
Magnetic field / G
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nanoparticles on the surface of TiO2 (in consistence with ref. [S3]), indicating that Au
nanoparticles locate on surface defect sites. This is also in accordance with the fact
that the surface defect sites are the trapping centers of photo-generated electrons,
which could reduce Au cations during photo-deposition. In another word, the surface
defects are the nucleation sites for Au during photo-deposition. Undoubtedly, higher
density of nucleation sites will lead to smaller size of Au nanoparticle.
470 468 466 464 462 460 458 456 454
Ti 2p1/2
Ti 2p3/2
Inte
nsity
/ a.
u.
Binding Energy / ev
Ti 2p
Au/TiO2-700
Au/TiO2-600
Au/TiO2-500
Au/TiO2-400
92 90 88 86 84 82 80
Au/TiO2-400
Au/TiO2-500
Au/TiO2-600
Au/TiO2-700
Au 4fAu 4f7/2
Inte
nsity
/ a.
u.
Binding Energy / eV
Au 4f5/2
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Figure S3 Au 4f, Ti 2p and O 1s XP spectra of Au/TiO2 samples, and Ti 2p, O 1s
XP spectra of TiO2
536 534 532 530 528 526
Inte
nsity
/ a.u
.
Binding Energy / eV
Au/TiO2-700
Au/TiO2-600
Au/TiO2-500
Au/TiO2-400
O 1s
531.6
529.6
536 534 532 530 528 526
533.0531.6
Inte
nsity
/ a.u
.
Binding Energy / eV
529.6
TiO2-700
TiO2-600
TiO2-500
TiO2-400
O 1s
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Figure S4 Light absorption spectra of Au/TiO2 samples and the relationship between
the absorption intensity of the SPR band at λ=550 nm and Au particle size
Figure S5 Hydrogen evolution during methanol photocatalytic reforming
over Au/TiO2 samples under visible light (400~780 nm) irradiation
300 400 500 600 700 8000
5
10
15
20
25
30
Kube
lka-
Mun
k Fu
nctio
n
Wavelength / nm
Au/TiO2-400 Au/TiO2-500 Au/TiO2-600 Au/TiO2-700
2 4 6 8 104
5
6
7
8
9
10
11
K-M
func
tion
Au cluster size / nm
0 1 2 3 4 50
10
20
30
40
50
60
70
Time-on-stream / h
H 2 pro
duct
ion
/ µm
olg ca
t-1
Au/TiO2-400 Au/TiO2-500 Au/TiO2-600 Au/TiO2-700
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Figure S6 Hydrogen evolution during methanol photocatalytic reforming
over TiO2 and Au/TiO2 samples under UV (320~400 nm) and UV-Vis
(320~780 nm) light irradiation
0
100
200
300
400
500
600TiO2-400 TiO2-500 TiO2-600 TiO2-700
UV-vis UV
H 2 pro
duct
ion
/ µm
ol g
cat-1
Time-on-stream / h0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 5
0
20
40
60
80
100Au/TiO2-400 Au/TiO2-500 Au/TiO2-600 Au/TiO2-700
UV-vis UV
H 2 pro
duct
ion
/ mm
ol g
cat-1
Time-on-stream / h0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 5
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Figure S7 The relationship between the SPR intensity of Au nanoparticles
and Δ reaction rate (Δ= RateUV-Vis – RateUV - RateVis)
Figure S8 Fluorescence spectra of Au/TiO2 under UV light irradiation and the
time-dependent fluorescence intensity at 426 nm with/without the presence of Fe3+
2 4 6 8 104
5
6
7
8
9
10
11
Au/TiO2-500
Au/TiO2-600
Au/TiO2-700
Au cluster size
SPR
inte
nsity
/ K-
M F
unct
ion
Au/TiO2-400
-1k
0
1k
2k
3k
4k
5k
6k
7k
∆ Re
actio
n ra
te /
µmol
h-1g ca
t-1
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-400
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-500
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-600
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-700
45 min30 min15 min 0 min
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-500
Au/TiO2-500 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-600
Au/TiO2-600 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-700
Au/TiO2-700 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-400
Au/TiO2-400 with Fe3+
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Figure S9 Fluorescence spectra of Au/TiO2 under visible light irradiation and the
time-dependent fluorescence intensity at 426 nm with/without the presence of Fe3+
Figure S10 Fluorescence spectra of Au/TiO2 under UV-visible light irradiation and the
time-dependent fluorescence intensity at 426 nm with/without the presence of Fe3+
350 400 450 500 550 600
0
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-400
45 min30 min15 min 0 min
350 400 450 500 550 600
0
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-500
45 min30 min15 min 0 min
350 400 450 500 550 600
0
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-600
45 min30 min15 min 0 min
0 10 20 30 40 500
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-600
Au/TiO2-600 with Fe3+
0 10 20 30 40 500
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-500
Au/TiO2-500 with Fe3+
0 10 20 30 40 500
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-400
Au/TiO2-400 with Fe3+
0 10 20 30 40 500
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-700
Au/TiO2-700 with Fe3+
350 400 450 500 550 600
0
50
100
150
200
Au/TiO2-700
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-400
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-500
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-600
45 min30 min15 min 0 min
350 400 450 500 550 6000
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Wavelength / nm
Au/TiO2-700
45 min30 min15 min 0 min
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-400
Au/TiO2-400 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-700
Au/TiO2-700 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-600
Au/TiO2-600 with Fe3+
0 10 20 30 40 500
1000
2000
3000
4000
5000
6000
7000
8000
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
Au/TiO2-500
Au/TiO2-500 with Fe3+
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Figure S11 The formation of OH radicals from the reductive and oxidative
pathway under different irradiations as determined by fluorescence spectra
Figure S12 Fluorescence spectra of Au colloid under visible light irradiation and
the time-dependent fluorescence intensity at 426 nm in the presence of Fe3+
Inlet: TEM of Au colloid
0
10
20
30
40
50
60
Re
duct
ive
/ Oxi
dativ
e
UV Vis UV-Vis
Au/TiO2-400 Au/TiO2-500 Au/TiO2-600 Au/TiO2-700
0 20 40 600
50
100
150
200
Emis
sion
inte
nsity
/ a.
u.
Irradiation time / min
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Figure S13 Fluorescence intensity caused by trapped OH radicals at time-on-stream
of 30 min with/without the presence of Fe3+ under different irradiations
Table S1 Physicochemical properties of Au/TiO2 samples under study
Samples Size (nm) a Au
wt.% b
SBET
(m2/g)
Hydroxyl groups % c
TiO2 Au Before PD After PD Δ d
Au/TiO2-400 16.6 9.4 3.94 121.6 30.5 17.1 13.4
Au/TiO2-500 19.4 7.5 3.97 69.4 36.6 18.8 17.8
Au/TiO2-600 26.8 5.3 3.92 43.3 42.3 17.6 24.7
Au/TiO2-700 36.5 3.1 3.95 20.9 49.3 16.2 33.1 a Average size estimated from TEM observation b Measured by ICP c Estimated from O 1s XP spectra d Difference in the percentage of hydroxyl groups before and after photo-deposition
0
10
20
30
40
TiO2-70
0
TiO2-60
0
TiO2-50
0
UV-Vis Vis UV
Fluo
resc
ence
inte
nsity
/ a.
u.
TiO2-40
0without Fe3+
0
2
4
6
8
TiO2-40
0
TiO2-70
0
TiO2-60
0
TiO2-50
0
UV-Vis Vis UV
Fluo
resc
ence
inte
nsity
/ a.
u. with Fe3+
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References
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[S4] D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Lchikawa, S. Tanaka and T. Hirai, J.
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