Colloidal Nanocrystals of Orthorhombic Cu2ZnGeS4: Phase ...

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c Department of Chemistry, National University of Singapore, Singapore 117543. ... S3. 25. 30. 35. 40. 45. 50. 55. 60 o o tt o o,t t tt t o o o. (a) OM + OA. #. #. #. #.
Electronic Supplementary Material (ESI) for Nanoscale. This journal is © The Royal Society of Chemistry 2015

Supporting Information Colloidal Nanocrystals of Orthorhombic Cu2ZnGeS4: PhaseControlled Synthesis, Formation Mechanism and Photocatalytic Behavior Cong-Min Fan,‡a,b Michelle D. Regulacio,‡a Chen Ye,a,c Suo Hon Lim,a Shun Kuang Lua,d Qing-Hua Xu,c Zhili Dong,d An-Wu Xu*b and Ming-Yong Han*a ‡ a b

These authors contributed equally to this work. Institute of Materials Research and Engineering, A*STAR, Singapore 117602. E-mail: [email protected] Division of Nanomaterials and Chemistry, Hefei National Laboratory for Physical Sciences at Microscale, Department of Chemistry, University of Science and Technology of China, Hefei 230026, P. R. China. E-mail: [email protected] c Department of Chemistry, National University of Singapore, Singapore 117543. d School of Materials Science & Engineering, Nanyang Technological University, Singapore 539798.

Ni

Counts (a.u.)

SK

CuK ZnK Ni

SK

2

4

6

8

Energy (keV)

GeK

CuK ZnK

GeK 10

12

Figure S1. EDX spectrum of orthorhombic Cu2ZnGeS4 (CZGS) nanocrystals. The Ni signals are attributed to the Ni TEM grid.

S1   

2p

Zn 2p

3/2

Intensity (a.u.)

Intensity (a.u.)

Cu 2p

2p

1/2

960

956

952

948

944

940

936

932

928

1/2

1048

1044

1032

1028

1024

1020

2p

S 2p

3d

5/2

3/2

2p

1/2

3/2

34

1036

Binding Energy (eV)

3d

36

1040

Intensity (a.u.)

Intensity (a.u.) 38

3/2

2p

Binding Energy (eV)

Ge 3d

2p

32

30

Binding Energy (eV)

28

26

168

166

164

162

160

158

Binding Energy (eV)

Figure S2. High-resolution XPS analysis of orthorhombic CZGS nanocrystals showing the Cu 2p (blue), Zn 2p (green), Ge 3d (red) and S 2p (purple) spectra.

S2   

o t

(a) OM + OA o,t

o o

t o

tt

Intensity (a.u.)

#*

#

* oo

o

o

o t t

(b) OM + TOP

#

#

* o

o (c) OM + t-DDT o o

o o

25

o

30

35

40

45

50

55

o 60

2-Theta (deg)

Figure S3. XRD pattern of the nanocrystals obtained when oleylamine (OM) is paired with (a) oleic acid (OA), (b) trioctylphosphine (TOP), and (c) tert-dodecanethiol (t-DDT). The solvent mixtures were prepared using 9:1 v/v ratio (e.g. 9 mL OM + 1 mL t-DDT). The peaks marked with red t and red o are attributed to the presence of tetragonal-phase (JCPDS #25-0327) and orthorhombic-phase (JCPDS #26-0572) CZGS, respectively. A blue asterisk is used to denote the presence of Ge (JCPDS #04-0545) whereas a green hash sign is used to mark the presence of Cu3Ge (JCPDS #06-0693).

S3   

CuCl2 + Zn(ac)2 + GeCl2.dioxane

o,t

Intensity (a.u.)

o,t

o o t t

20

o,t o o,t

o

30

40

50

o

o

60

70

2-Theta (deg)

Figure S4. XRD pattern of the nanocrystals obtained when CuCl2 was used as the Cu precursor instead of Cu(dtc)2. The peaks marked with red t and red o are attributed to the presence of tetragonal (JCPDS #25-0327) and orthorhombic (JCPDS #26-0572) CZGS, respectively.

(a)

Ni

Intensity (a.u.)

Counts (a.u.)

SK

(b) CuK Ni

ZnK

ZnK

SK

CuK 20

30

40

50

2-Theta (deg)

60

70

2

3

4

5

6

7

8

9

10

11

Energy (keV)

(c)

100 nm

Figure S5. (a) XRD pattern, (b) EDX spectrum and (c) TEM image of the material obtained at 100 C. The blue pattern in (a) is from the standard JCPDS file for wurtzite ZnS (JCPDS #751547). The Ni signals in (b) are attributed to the Ni TEM grid. S4   

Intensity (a.u.)

Monoclinic Cu1.75S

25

30

35

40

45

50

55

60

2-Theta (deg)

Figure S6. XRD pattern of the material obtained when Cu(dtc)2 is heated solely in OM:t-DDT (9:1, v:v) at 100 C. The blue pattern at the bottom is from the standard JCPDS file for monoclinic Cu1.75S (JCPDS #23-0958).

S5   

CuK

Counts (a.u.)

ZnK

(d)

Ni

(c)

Ni

Ni

GeK

CuK

GeK

ZnK

Ni

Ni

(b)

Ni Ni

Ni

(a) 6

7

8

9

10

11

12

Energy (keV)

Figure S7. EDX spectra of the nanocrystals that form at different stages of the reaction: (a) 100 C; (b) 200 C; (c) 300 C, 0 min; (d) 300 C, 60 min. The Ni signals are attributed to the Ni TEM grid.

S6   

Cu(dtc)2 + ZnCl2 + GeCl2.dioxane o,t

Intensity (a.u.)

o,t o o o

o

o,t

t

o

o

o

t 20

30

40

50

60

70

2-Theta (deg)

Figure S8. XRD pattern of the nanocrystals obtained when ZnCl2 was used as the Zn precursor instead of Zn(ac)2. The peaks marked with red t and red o are attributed to the presence of tetragonal (JCPDS #25-0327) and orthorhombic (JCPDS #26-0572) CZGS, respectively.

Cu(dtc)2 + Zn(ac)2 + GeI4

o,t

Intensity (a.u.)

o,t

o,t o

o o t

20

30

o 40

o 50

60

70

2-Theta (deg)

Figure S9. XRD pattern of the nanocrystals obtained when GeI4 was used as the Ge precursor instead of GeCl2.dioxane. The peaks marked with red t and red o are attributed to the presence of tetragonal (JCPDS #25-0327) and orthorhombic (JCPDS #26-0572) CZGS, respectively.

S7   

(312)/(116)

25

30

35

(224)

(200)/(004)

Intensity (a.u.)

(220)/(204)

(112)

CuCl2 + ZnCl2 + GeI4 + S

40

45

50

55

60

2-Theta (deg)

Figure S10. XRD pattern of the nanocrystals obtained when the precursors used are CuCl2, ZnCl2, GeI4 and S. The solvent used is OM. All the diffraction peaks can be indexed according to the standard diffraction pattern of tetragonal CZGS (JCPDS #25-0327).

S8   

(a)

1.4

Absorbance (a.u.)

1.2

0h 1h 2h 3h 4h 5h 6h

without illumination

1.0 0.8 0.6 0.4 0.2 0.0 350

400

450

500

550

600

650

Wavelength (nm)

(b)

1.4

Absorbance (a.u.)

1.2

0h 1h 2h 3h 4h 5h 6h

without CZGS nanocrystals

1.0 0.8 0.6 0.4 0.2 0.0 350

400

450

500

550

600

650

Wavelength (nm)

Figure S11. Temporal evolution of the absorption spectra of an aqueous RhB solution (a) in the presence of orthorhombic CZGS nanocrystals without illumination (performed in the dark) and (b) in the absence of orthorhombic CZGS nanocrystals with visible-light illumination.

S9