Electronic Supplementary Information (ESI) for:

Facile precursor-mediated synthesis of porous core-shell-type Co3O4

octahedra with large surface area for photochemical water oxidation

Li-Jing Zhou,a Yongcun Zou,a Guo-Dong Li,a Xiaoxin Zou,a* Jun Zhao,a Meihong Fan,a Yipu Liu,a and Dejun Wanga,b

a State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry,

Jilin University, Changchun 130012, P.R. China

b Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China

* E-mail: X. Zou, chemistryzouxx@gmail.com

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Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2014

Experimental Section

Synthesis of Co-PDO: A solution containing cobalt acetate tetrahydrate (Co(CH3COO)2•4H2O, 0.31

mmol) and 1,3-propanediol (PDO, 20 mL) was placed in a Teflon-lined stainless steel autoclave. The

autoclave was then treated at 160 oC for 6 h. After cooling to room temperature naturally, the

solution was centrifuged to recover the solid precipitate, which was washed several times with

ethanol and dried in an oven at 80 °C, resulting in Co-PDO.

Preparation of Co3O4 materials from Co-PDO: Three Co3O4 samples were prepared by simply

calcining Co-PDO in air at 200, 300 and 400 oC for 2 h, respectively. The corresponding Co3O4

materials were labeled as Co3O4-1, Co3O4-2, and Co3O4-3, respectively.

General Characterization: The powder X-ray diffraction (XRD) patterns were recorded on a Rigaku

D/Max 2550 X-ray diffractometer using CuKα radiation (λ = 1.5418 Å) operated at 200 mA and 50

kV. The scanning electron microscopic (SEM) images were taken on a JEOL JSM 6700F electron

microscope. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM)

images were obtained on a Philips-FEI Tecnai G2S-Twin with a field emission gun operating at 200

kv. The Brunauer-Emmett-Teller surface areas and Nitrogen adsorption-desorption isotherms of the

samples were measured by using a Micromeritics ASAP 2020M system. The infrared (IR) spectra

were recorded on a Bruker IFS 66V/S FTIR spectrometer using KBr pellets. The thermal gravimetric

analysis curve was recorded on a NETZSCH STA 449C TG thermal analyzer from 25 to 800 °C at a

heating rate of 10 oC/min in air. The X-ray photoelectron spectroscopy (XPS) was performed on an

ESCALAB 250 X-ray photoelectron spectrometer with a monochromated X-ray source (Al Kα hυ =

1486.6 eV).

Photochemical Water Oxidation: The water oxidation reaction with the as-obtained Co3O4-1

material (5 mg) as catalyst was performed in a Na2SiF6-NaHCO3 buffer solution (20 mL, pH = 5.8),

in which [Ru(bpy)3]Cl2·6H2O (15 mg) as sensitizer, sodium persulfate (65 mg) as sacrificial electron

acceptor and Na2SO4 (195 mg) were added. The reaction solution was magnetically stirred during the

whole photocatalytic testing. Before light irradiation, the system was bubbled by N2 to eliminate air

in the reaction system and the temperature of the system during photocatalytic reaction was kept

around 20 oC by a continuous flow of water. The evolved gas was detected in situ

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using an online Dissolved Oxygen Meter. There is a rubber O-ring between the electrode (Dissolved

Oxygen Meter) and quartz cell to maintain the tightness of the reaction system. For comparison, the

catalytic activities of Co3O4-2, Co3O4-3 and a commercially available Co3O4 material were also

measured under the same conditions as for Co3O4-1 by keeping the same weight of samples in each

case.

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Fig. S1 XRD patterns and SEM images (Scale bar = 10 μm) of the Co-PDO precursors synthesized

with different Co2+ concentrations and different temperatures. It was worth noting here that the

crystal structure and morphology of Co-PDO precursors remained unchanged and the XRD pattern

showed diffraction peaks similar to those of previously-reported polyols-based metal alkoxides.[S1]

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5 10 15 20 25 30 35 40 45 50

31 mmol/L 160 oC

23.25 mmol/L 160 oC

15.5 mmol/L 160 oC

7.75 mmol/L 160 oC

Inte

nsity

(a.u

.)

2 Theta (o)

3.1 mmol/L 160 oC

5 10 15 20 25 30 35 40 45 50

200 oC 15.5 mol/L

180 oC 15.5 mol/L

160 oC 15.5 mol/L

Inte

nsity

(a.u

.)

2 Theta (o)

140 oC 15.5 mol/L

Fig. S2 IR spectrum of the Co-PDO precursor. The broad IR absorption band at ~3429 cm-1 is

attributed to hydrogen-bound hydroxyl groups, and the absorption band at ~2808-2906 cm-1 is

characteristic of the C-H stretching vibrations. In addition, the bands located between 1500 and 800

cm-1 are generally assigned to C-C, C-C-O and C-O-Co groups; whereas the bands below 600 cm-1

are generally assigned to Co-O. Similar IR results were also observed previously for other metal

alkoxides.[S1]

Fig. S3 Co 2p XPS spectrum for the Co-PDO precursor. Two XPS peaks were detected at 780.8 and

796.6 eV, indicating the presence of Co (II) species in the Co-PDO precursor.

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4000 3200 2400 1600 800

28082906

3429

Tran

smitt

ance

(%)

Wavenumber (cm-1)

810 800 790 780 770

796.6780.8

Intensity (a.u.)

Binding energy (eV)

Co2p

Fig. S4 TG curve measured in air for the Co-PDO precursor. TG analysis of the Co-PDO precursor

was carried out in air from 25 to 800 oC. Before 100 oC, the weight loss of 2.5% can be attributed to

evaporation of the absorbed water molecules on the Co-PDO surface. The Co-PDO completely

decomposed at around 250 oC with a total weight loss of ~64 %. From the weight loss values it is

estimated that the cobalt content of the Co-PDO precursor was calculated to be ~22.6 wt.%.

Fig. S5 A simulation of how an octahedral particle can show a hexagonal shape during TEM

measurement. The arrow in Fig. S5A means the direction of light (electron).

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0 100 200 300 400 500 600 700 8000102030405060708090

100

64%

Wei

ght (

%)

Temperature (oC)

Fig. S6 SEM image of Co3O4-1.

Fig. S7 SEM image of a broken Co3O4-1 particle.

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Fig. S8 HRTEM images of the Co3O4-1 material.

Fig. S9 IR spectra of Co3O4-1, Co3O4-2 and Co3O4-3. Comparison of the IR spectra of the Co3O4

materials and the Co-PDO precursor revealed that upon thermal treatment the IR absorption bands

for organic component in Co-PDO (Fig. S2) disappeared, indicating the complete conversion of Co-

PDO into Co3O4. The broad IR absorption band around 3394 cm-1 is due to stretching vibrations of -

OH, and the absorption bands at ~574.2 and 670.1 cm-1 are ascribed to Co-O.[S2]

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4000 3500 3000 2500 2000 1500 1000 500

574.2670.1

3394

Co3O4-3

Co3O4-2

Tran

smitt

ance

Wavenumber (cm-1)

Co3O4-1

Fig. S10 (A) XRD patterns of Co3O4-1, Co3O4-2 and Co3O4-3. (B) N2 adsorption–desorption

isotherms of Co3O4-2 and Co3O4-3. SEM images of (C,D) Co3O4-2 and (E,F) Co3O4-3. TEM images

of (G) Co3O4-2 and (H) Co3O4-3. Based on the above characterizations, it is concluded that 1) like

Co3O4-1, Co3O4-2 and Co3O4-3 also maintain the octahedron-like morphology of the Co-PDO

precursor; 2) different with Co3O4-1, Co3O4-2 and Co3O4-3 do not have a core-shell structure; and 3)

Co3O4-2 (61 m2/g) and Co3O4-3 (20 m2/g) have much lower BET surface areas than Co3O4-1 (190

m2/g).

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C D

E F

G H

10 20 30 40 50 60 70 80

ACo3O4-3

Co3O4-2

Inte

nsity

(a.u

.)

2 Theta (o)

Co3O4-1

0.0 0.2 0.4 0.6 0.8 1.0

0

50

100

150B

Co3O4-2 Co3O4-3

Volu

me

(cm

3 /g)

P/P0

Fig. S11 (A) XRD patterns of Co3O4-1 before (0 min) and after (60 min) photochemical water

oxidation reaction; (B) SEM image of Co3O4-1 after photochemical water oxidation reaction; (C)

Si2p and (D) O1s XPS spectra of before (0 min) and after (60 min) photochemical water oxidation

reaction.

10

10 20 30 40 50 60 70 80

A

0 min

60 min

Inte

nsity

(a.u

.)

2 Theta (o)

115 110 105 100 95

C

0 min

Inte

nsity

(a.u

.)

Binding energy (eV)

60 min

Si 2p105.0

540 538 536 534 532 530 528 526

DSi-O

Co-O

530.060 min

Inte

nsity

(a.u

.)

Binding energy (eV)

0 min

O 1s532.8

B

Table S1. TOFs of some recently-reported solid-state catalysts for photo- or electrochemical water oxidation

Catalyst TOF (S-1 Per Co/Mn atom) ref

Co3O4-12.86 ×10-4 This Work

Co3O4 supported in mesoporous silica 2.12 ×10-4 ~ 4.05 ×10-4Angew. Chem. Int. Ed. 2009,48,1841

ACS Catal. 2012, 2, 2753

Hierarchical porous Co3O42.4 ×10-4 J. Am. Chem. Soc. 2013, 135, 4516

Co3O41.4×10-4

NiCo2O47.9 ×10-5

J. Chem. Soc., Faraday Trans. 1, 1988, 84, 2795

Co3O4 Nanoparticle 1.87 ×10-2 ~ 9.3 ×10-2 J. Phys. Chem. C 2009, 113, 15068

Co3O4 film7.8 ×10-3 Electrochim. Acta 1981, 26, 1319

Co3O4 electrode 2.76 ×10-2 Electrochem. Commun. 2007, 9, 1369

Li2Co2O41.0 × 10-3 Angew. Chem. Int. Ed. 2012, 51, 1616

LaCoO36.5 × 10-4 Phys. Chem. Chem. Phys., 2012, 14,

5753

-MnO23 ×10-5

~ 5 × 10-6 J. Am. Chem. Soc. 2010, 132, 11467

ESI references:

[S1] a) J. Zhao, X. Zou, L.-J. Zhou, L.-L. Feng, P.-P. Jin, Y.-P. Liu, G.-D. Li, Dalton Trans., 2013,

2013, 42, 14357; b) D. Larcher, G. Sudant, R. Patrice, J.-M. Tarascon, Chem. Mater., 2003, 15,

3543; c) J. Zhao, X.-X. Zou, J. Su, P.-P. Wang, L.-J. Zhou, G.-D. Li, Dalton Trans., 2013, 42, 4365.

[S2] X. Zou, J. Su, R. Silva, A. Goswami, B. R. Sathe, T. Asefa, Chem. Commun., 2013, 49, 7522.

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