synergetic promotion of photocatalytic activity of tio by ... · in the region of 200-700 nm on a...

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

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2013

mailto:[email protected]

2

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


3

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


4

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.


5

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


6

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


7

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


8

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


9

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



10

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


11

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


350 400 450 500 550 6000

1000

2000

3000

4000

5000

6000

7000

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm

Au/TiO2-600


350 400 450 500 550 6000

1000

2000

3000

4000

5000

6000

7000

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm

Au/TiO2-700


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.


Au/TiO2-600


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-700


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-400



12

Figure S9 Fluorescence spectra of Au/TiO2 under visible light irradiation and the


Figure S10 Fluorescence spectra of Au/TiO2 under UV-visible light irradiation and the


350 400 450 500 550 600

0

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm

Au/TiO2-400


350 400 450 500 550 600

0

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm

Au/TiO2-500


350 400 450 500 550 600

0

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm

Au/TiO2-600


0 10 20 30 40 500

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-600


0 10 20 30 40 500

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-500


0 10 20 30 40 500

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-400


0 10 20 30 40 500

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-700


350 400 450 500 550 600

0

50

100

150

200

Au/TiO2-700

Emis

sion

inte

nsity

/ a.

u.

Wavelength / nm


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


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


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


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


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

8000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-400


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

8000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-700


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

8000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-600


0 10 20 30 40 500

1000

2000

3000

4000

5000

6000

7000

8000

Emis

sion

inte

nsity

/ a.

u.


Au/TiO2-500



13

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


0 20 40 600

50

100

150

200

Emis

sion

inte

nsity

/ a.

u.



14

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+


15

References

[S1] I. Fenoglio, G. Greco, S. Livraghi and B. Fubini, Chem. Eur. J. 2009 , 15 , 4614.

[S2] J. M. Coronado and J.Soria, Catal. Today, 2007, 123, 37.

[S3] Y. Shiraishi, D. Tsukamoto, Y. Sugano, A. Shiro, S. Ichikawa, S. Tanaka and T.

Hirai, ACS Catal., 2012, 2, 1984.

[S4] D. Tsukamoto, Y. Shiraishi, Y. Sugano, S. Lchikawa, S. Tanaka and T. Hirai, J.

Am. Chem. Soc., 2012, 134, 6309


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