Supporting Information

Wiley-VCH 2012

69451 Weinheim, Germany

Microwave-Assisted Synthesis of Porous Ag2SAg Hybrid Nanotubeswith High Visible-Light Photocatalytic Activity**Wenlong Yang, Lei Zhang, Yong Hu,* Yijun Zhong, Hao BinWu, and XiongWen (David) Lou*

anie_201206715_sm_miscellaneous_information.pdf

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Experimental details

Uniform Ag2CO3 NRs were prepared by a facile precipitation process. In a typical synthesis, 0.5

mmol of AgNO3 and 1.0 g of polyvinylpyrrolidone (PVP, MW~ 58K) were dissolved in 20 mL of

deionized (DI) water to form a clear solution, followed by a dropwise addition of 20 mL of

pre-prepared NaHCO3 aqueous solution (0.05 M). After several minutes, the solution turned grey,

indicating the initial formation of Ag2CO3 NRs. The mixture was continuously stirred for 1 h at room

temperature and collected by centrifugation. After washing with DI water and ethanol for three times

each, the as-prepared Ag2CO3 NRs were dried at 60 C for 6 h.

Porous Ag2S-Ag heterostructue nanotubes (HSNTs) were prepared as follows: ~35 mg of Ag2CO3

NRs and a predetermined amount of thioacetamide (TAA) were added into a round-bottom ask and

dispersed in 20 mL of ethanol with the assistance of ultrasonication for 10 min. Then, the above

mixture was placed in a microwave reuxing system and irradiated at 400 W for 15 min. The final

products were collected by centrifugation and washed with ethanol and DI water three times each

before drying at 60 C for 6 h. To investigate the effect of TAA on the formation of porous Ag2S-Ag

HSNTs, different concentrations of TAA were used in the suldation process, while keeping other

conditions unchanged.

Powder X-ray diffraction (XRD) measurement of the samples was performed with a Philips

PW3040/60 X-ray diffractometer using Cu K radiation at a scanning rate of 0.06 deg s-1. Scanning

electron microscope (SEM) was performed with a Hitachi S-4800 scanning electron micro-analyzer

with an accelerating voltage of 15 kV. Transmission electron microscope (TEM) and high-resolution

transmission electron microscope (HRTEM) were conducted at 200 kV with a JEM-2100F

eld-emission TEM, equipped with energy-dispersive X-ray spectroscopy (EDS) analysis for elemental

analysis. The absorption spectra were measured using a PerkinElmer Lambda 900 UV-vis

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spectrophotometer at room temperature. Further evidence for the composition of the products was

inferred from X-ray photoelectron spectroscopy (XPS), using an ESCALab MKII X-ray photoelectron

spectrometer with Mg K X-ray as the excitation source.

The photocatalytic activities of porous Ag2S-Ag HSNTs were evaluated by photocatalytic

degradation of methyl orange (MO) and photocatalytic reduction of Cr(VI) under visible-light

irradiation of a 500 W Xe lamp with a 420 nm cutoff filter. The reaction cell was placed in a sealed

black box with a window on the top, and the cutoff filter was placed to provide visible-light irradiation.

In a typical process, 8 mg of the as-prepared porous Ag2S-Ag HSNTs as the photocatalyst was added

into 20 mL of a MO solution (5 mg L-1

) or 20 mL of Cr(VI) solution (10 mg L-1

based on Cr in a dilute

K2Cr2O7 solution). After the photocatalyst was dispersed in the solution with an ultrasonic bath for 5

min, the solution was stirred for 2 h in the dark to reach adsorption equilibrium and then was exposed

to visible-light irradiation. The photocatalysts were removed by centrifugation at given time intervals,

and the MO concentration was measured colorimetrically at 464 nm using the UVvis spectroscopy.

The Cr(VI) reduction was determined colorimetrically at 540 nm using the diphenylcarbazide (DPC)

method. The OH radical reaction was conducted following a similar method reported previously,[1-3]

and the detailed experimental procedure is provided in the Supporting Information.

Cr(VI) reduction was determined colorimetrically at 540 nm using the diphenylcarbazide (DPC)

method. 1 mL of solution after photocatalytic reduction of Cr(VI) was mixed with 9 mL of 0.2 M

H2SO4 in a 10 mL volumetric ask. Subsequently, 0.2 mL of freshly prepared 0.25% (w/v) DPC in

acetone was added to the volumetric ask. After vortexing the mixture for about 15-30 s, it was

allowed to stand for 10-15 min so as to ensure full color development. Using deionized water as

reference the red-violet to purple color formed was then measured at 540 nm.

The OH radical reactions were performed as follows. 5 mg of the different samples was suspended

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in 8 mL of aqueous solution containing 10 mM of NaOH and 5 mM of terephthalic acid (TA). Before

exposing to visible-light, the suspension was stirred in the dark for 10 min. After irradiated for 10 min,

the solutions were centrifuged for fluorescence spectroscopy measurements. A fluorescence

spectrophotometer was used to measure the fluorescence signal of the 2-hydroxy-terephthalic acid

(TAOH) generated. The excitation light wavelength used in recording fluorescence spectra was 320

nm.

[1] T. Hirakawa, Y. Nosaka, Langmuir 2002, 18, 3247.

[2] Y. Liu, Y. Hu, M. J. Zhou, H. S. Qian, X. Hu, Appl. Catal. B-Environ. 2012, 125, 425.

[3] W. L. Yang, Y. Liu, Y. Hu, M. J. Zhou, H. S. Qian, J. Mater. Chem. 2012, 22, 13895.

Figure S1. SEM image of the as-obtained Ag2S-Ag hybrid in water under microwave irradiation in-situ

sulfidation for 10 min.

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Figure S2. XRD patterns of the as-prepared Ag2CO3 NRs, other porous Ag2S-Ag HNSTs and pure

Ag2S obtained in the presence of different TAA concentrations under microwave irradiation process.

10 20 30 40 50 60 70 80

Ag2S

H-1

H-3

I

2/ O

Ag2CO

321

0

41

1

40

1

22

1

22

0

11

1

11

0

Ag 31

1

22

0

20

011

1

01

5

22

3

21

3

12

31

31

20

00

31

10

312

11

21

12

0

11

1

11

1

11

2

Ag2SAgAg

2CO

3

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Figure S3. EDS spectrum of the as-prepared porous Ag2S-Ag HSNTs (CTAA= 3.5 mM).

Table S1. Composition of the as-prepared porous Ag2S-Ag HSNTs. .

Samples Atomic (%) S K Ag L

Molar ratio Ag2S : Ag

H-1 13.87 86.13 0.24

H-2 21.88 78.12 0.64

H-3 Ag2S

25.76 74.24 33.29 66.71

1.13 ---

0 1 2 3 4 5

S

SAg

Ag

Energy(KeV)

Inte

ns

ity

(CP

S)

Ag

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Figure S4. (a) The line-scanning EDS analysis of S element (red curve) and Ag element (green curve)

for one individual Ag2S-Ag hybrid nanotube (sample H-2). The elemental mapping EDS images of Ag

(b) and S (c).

Figure S5. SEM images of the as-prepared pure Ag nanoparticles (a) obtained in the absence of TAA,

H-1 (b), H-3 (c), and pure Ag2S (d).

a b

d c

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Figure S6. XPS spectra of as-prepared porous Ag2S-Ag HSNTs. a) survey spectrum, b) Ag3d binding

energy spectrum and c) S2p binding energy spectrum.

Surface information on the Ag2S-Ag HSNTs was further acquired with the XPS technique. The

peaks at 368.2 and 374.2 eV in the Ag 3d photoelectron spectrum (Figure S6b) are in good agreement

with the binding energies of Ag 3d5/2 and Ag 3d3/2 of the metallic Ag0. Whereas, the peaks at 367.8

and 373.8 eV should be assigned to those of Ag 3d5/2 and Ag 3d3/2 of Ag+ ions in the Ag2S. Thus, it is

understandable that both metallic state (Ag0) and Ag

+ ions are present in the hybrids. In addition, the

value of the electron binding energy of S (2P, 161.9 eV, in Figure S6c) is attributed to the S2-

in the

lattice of Ag2S.

0 200 400 600 800 1000

O1

s

Ag

3d

C1

s

Inte

ns

ity

(a

.u.)

Bingding energy (eV)

S2

pa

156 158 160 162 164 166 168 170 172

S2p

In

ten

sit

y (

a.u

.)

Bingding energy (eV)

161.9c

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Figure S7. Five cycles of the photodegradation of MO (a), and photocatalytic reduction of Cr(VI) (b)

using sample H-2 as the photocatalyst. After each test, the photocatalyst was collected and rinsed by

deionized water.

0.0

0.2

0.4

0.6

0.8

1.0 5th4th3rd2nd

C /

CO

t / min

1sta

30

0 300 300 300 300 300

0.0

0.2

0.4

0.6

0.8

1.0 5th4th3rd2nd

C /

CO

t / time

1stb

800 800 800 800 800