Electronic Supplementary Information (ESI)
Tin Oxide with Tunable p-n Heterojunction for UV and Visible
Light Photocatalytic Activity Arun Kumar Sinha
1, P.K. Manna
2, Mukul Pradhan
1, Chanchal Mondal
1, S. M. Yusuf
2 and
Tarasankar Pal1
1Department of Chemistry
Indian Institute of Technology, Kharagpur-721302, India
2 Solid State Physics Division, Bhabha Atomic Research Centre,
Mumbai 400 085, India
*E-mail: [email protected]
ESI 1:
1. Materials:
All the reagents were of AR grade. Triple distilled water was used throughout the
experiment. SnCl2.2H2O was obtained from E Merck. NaOH was purchased from BDH
Company, Mumbai.
2. Preparation of SnO nanoplate:
Pure SnCl2.2H2O was finely powdered by using an agate motor & pestle and a
measured amount (10 gm) was mixed with 30 mL NaOH (5.0 M) solution. Within 60
minutes of ultrasonication the white powder changes to a blue-black mass. The blue-
black SnO sample was obtained at the solid–liquid interface i.e. the interface between
powder SnCl2.2H2O and NaOH solution. The hydrolysis and dehydration steps occured
simultaneously.
Hydrolysis step SnCl2.2H2O + NaOH (5 M) → Sn6O4(OH)4 (white color) + 2NaCl
Dehydration step Sn6O4(OH)4 → SnO (Blue-black) + 3H2O
The blue-black SnO sample was produced slowly from the surface layer of SnCl2 powder
at the interface. The blue-black SnO was formed and washed with copious amount of
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water until pH of the washings lowered down to distilled water pH. The blue-black
sample was air dried and stored for further characterization.
3. Characterization Instruments:
1.1. UV-Visible study:
All absorption spectra for the degradation reaction were recorded in a chemito
spectrophotometer (India) and taking the solutions in a 1 cm quartz cuvette.
1.2. DRS study:
Reflectance spectra were measured using DRS (Diffuse Reflectance Spectra)
mode with a Cary model 5000 UV-vis-NIR spectrophotometer.
1.2. XRD-study:
XRD was done in a PW1710 diffractometer, Philips, Holland, instrument. The
XRD data were analyzed using JCPDS software.
1.3. Structural computational study:
The analysis of the X-ray diffraction pattern of SnO was done using the FullProf
program. This is free software and it is available in internet.
1.4. Raman-study:
Raman spectra were obtained with a Renishaw Raman Microscope, equipped with
a He–Ne laser excitation source emitting at a wavelength of 633 nm, and a Peltier cooled
(-70 °C) charge coupled device (CCD) camera.
1.5. XPS-study:
The chemical state of the element on the surface was analyzed by a VG Scientific
ESCALAB MK II spectrometer (UK) equipped with a Mg Kα excitation source (1253.6
eV) and a five-channeltron detection system.
1.6. FTIR-study:
FTIR studies were performed with a Thermo-Nicolet continuum FTIR
microscope.
1.7. BET-study:
Nitrogen adsorption-desorption measurements were performed at 77.3 K using a
Quantachrome Instruments utilizing the BET model for the calculation of surface areas.
The pore size distribution was calculated from the adsorption isotherm curves using the
Barrett-Joyner-Halenda (BJH) method.
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1.8. FESEM and EDS analysis:
FESEM analysis was performed with a supra 40, Carl-Zeiss Pvt. Ltd instrument
and an EDS machine (Oxford, Link, ISIS 300) attached to the instrument was used to
obtain the material morphology and composition.
1.9. TEM and HRTEM analysis:
TEM analysis was performed with an instrument H-9000 NAR, Hitachi, using an
accelerating voltage of 200 kV.
1.10. Thermo gravimetric analysis:
A differential scanning calorimetry tester (DSC131, Setaram Labsys, France) was
used to measure the phase change of SnO nanomaterial. During the test, nanopowders
were heated at a rate of 5 °C/min under an O2 atmosphere.
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ESI 2.
DR spectra of SnO nanocrystals and heat treated SnO samples
200 400 600 8000.0
0.3
0.6
0.9
1.2
1.5
1.8SnO (Room Temperature)
SnO (at 4000C)
SnO (at 8000C)
Ab
so
rban
ce (
a.u
.)
Wavelength (nm)
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ESI 3:
ESI 3a. XRD pattern of SnO nanoplates showing temperature dependent phase
transformation from SnO to SnO2 (a) and XRD spectrum of rutile phase of SnO2 obtained
after 800°C heat treatment (b).
10 20 30 40 50 60 7010 20 30 40 50 60 7010 20 30 40 50 60 70-1x10
3
0
1x103
2x103
3x103
a
2
8000C
7000C
4000C
2000C
RT
SnO2
SnO (room temperature)
Inte
nsit
y (
a.u
.)
6000C
20 30 40 50 60 70 80
0
50
100
150
200
250(3
21)
(202)
(301)
(112)
(310)
(002)
(220)
(211)
(200)
(101)
(110) SnO
2 at 800
0C b
Inte
nsit
y (
a.u
.)
2
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ESI 3b. Rietveld refined, observed (open circle) and calculated (solid line) XRD patterns
of (a) as prepared SnO, and SnO annealed at different temperatures (b) 200 C, (c) 400
C and (d) 800 C. The solid line at the bottom shows the difference between observed
and calculated patterns. Vertical lines show the positions of the Bragg peaks. The top,
middle and bottom layers of vertical lines in figure (c) indicate the Bragg peak positions
of SnO, SnO2 and Sn3O4, respectively.
0
1500
0
1500
10 20 30 40 50 60 70
0
200
0
700
Inte
nsity (
arb
. un
its)
As-prepared
200 C
800 C
2(deg.)
400 C
a
b
c
d
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ESI 4:
ESI 4a. A comparative view of (a) SnO litharge structure and (b) SnO2 rutile
structure
ESI 4b. (a) SnO4 square pyramidal network in SnO; (b) SnO6 octahedral network
in SnO2.
c
ba
c
ba
a b
Sn
Sn
OO
c
ba
c
ba
a b
c
ba
c
ba
baa
c
ba
c
ba
baa
a b
Sn
Sn
OO
a
c
b
Sn
O
a
a
c
b
a
c
b
c
bb
Sn
O
a
b
a
c
b
a
c
b
a
c
a
cc
b
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ESI 4c: Typical interatomic distances, and angles of SnO and SnO2, obtained from
the Rietveld refinement.
114.8(3)°Bond angles
Sn-O-Sn
89.1(9)°Bond angles
O1-Sn-O2
3.187(2) ÅBond length O1-O4
2.90(3) ÅBond length O1-O5
2.63(3) ÅBond length O1-O2
2.04(2) ÅBond length Sn-O5
2.06(2) ÅBond length Sn-O1
ValuesBond lengths and
bond angles of SnO2
114.8(3)°Bond angles
Sn-O-Sn
89.1(9)°Bond angles
O1-Sn-O2
3.187(2) ÅBond length O1-O4
2.90(3) ÅBond length O1-O5
2.63(3) ÅBond length O1-O2
2.04(2) ÅBond length Sn-O5
2.06(2) ÅBond length Sn-O1
ValuesBond lengths and
bond angles of SnO2
117.6(1)°Bond angles
Sn-O-Sn
80.6(7)°Bond angles
O1-Sn-O2
3.799 (2) ÅBond length O1-O4
2.69(9) ÅBond length O1-O2
2.22(3) ÅBond length Sn-O1
ValuesBond lengths and
bond angles of
SnO
117.6(1)°Bond angles
Sn-O-Sn
80.6(7)°Bond angles
O1-Sn-O2
3.799 (2) ÅBond length O1-O4
2.69(9) ÅBond length O1-O2
2.22(3) ÅBond length Sn-O1
ValuesBond lengths and
bond angles of
SnO
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ESI 4d: Structural parameters of SnO and SnO2, obtained from the Rietveld
refinement.
Inorganic Material SnO SnO2
Space Group P4/nmm P42/mnm
crystallographic unit
cell
a = b = 3.799(1) Å
c = 4.841(1) Å
a = b = 4.738(2) Å
c = 3.187(1) Å
Absolute position
And
Occupancy number
Sn (2c)
x = 1/4
y = 1/4
z = 0.238(1)
Occ = 1
Sn (2a)
x = 0
y = 0
z = 0
Occ = 1
Absolute position
And
Occupancy number
O (2a)
x = 3/4
y = 1/4
z = 0
Occ = 1
O (4f)
x = 0.304(5)
y = 0.304(5)
z = 0
Occ = 1
chi-square of the
pattern
χ2 = 2.13 χ2 = 1.97
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ESI 5.
Raman spectra of heat treated SnO nanoplates examined under laser power 100% (20
mW) and laser exposure time 30 sec.
200 400 600 800 1000
1000C
2000C
4000C
6000C
8000C
479.27308.97 779.47
638.62
Inte
nsity (
a.u
.)
Raman shift (cm-1)
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ESI 6.
Thermal analysis (TG-DTA) of SnO nameplates
The curve I represents the TG curve and the inflection region demonstrates the phase
change area of SnO material in relation with the temperature change. The significant
phase change from SnO to SnO2 via some intermediate (such as Sn3O4) took place at an
approximate temperature range of 300°-700°C and at 800°C the transformation of phase
becomes complete. In this case, DTA curves (black line) show exothermic peak because
there occurs one thermochemical reaction which is oxidative in nature.
200 400 600 8008200
8400
8600
8800
9000
9200
-100
-50
0
50
100
i=TG Curve
DT
G
g/m
inD
TA
mV
V
iii
ii
i
561.810C
TG
%
Temp ( 0C)
iii=DTA Curveii=DTG Curve)
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ESI 7.
XPS analysis of SnO nanoplates at different temperature. Survey scan (a), Sn 3d (b) and
O 1s (c) core level XPS spectra of SnO (room temperature), SnO (200°C), SnO (400°C)
and SnO (800°C) samples.
484 488 492 496 500
1x104
2x104
3x104
4x104
b
495.04
495.26
495.29
495.363d
3/2
3d5/2
486.62 RT
486.77 2000C
486.82 4000C
486.87 8000C
Inte
nsit
y (
a.u
.)
Binding Energy (eV)
526 528 530 532 534 536
16000
20000
24000
C
531.12 8000C
530.99 4000C
530.95 2000C
530.75 RT
Inte
nsit
y (
a.u
.)
Binding energy (eV)
0 200 400 600 800 1000
Inte
nsit
y (
a.u
.)
8000C
4000C
2000C
RT
a
3P
1/2
3P
3/2
C 1
s
O 1
s
Sn
3d
5/2
Sn
3d
3/2
Binding Energy (eV)
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ESI 8.
FTIR spectra of powder SnO sample at different temperature. (i) neat SnCl22H2O (ii) as
prepared SnO at RT (iii) SnO at 200° C (iv) SnO at 400° C (v) SnO at 600° C and (vi)
SnO at 800° C.
ESI 8 shows FTIR spectra SnO nanocrystals but at different temperatures. Thus FTIR
conclusively speaks for the non-hygroscopic behavior of SnO material. It is also observed
that as SnO is oxidized to SnO2 and the sample became hygroscopic. So a broad band at
3438.90 cm-1
appeared for SnO2 material at 600 and 800°C.
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
500 1000 1500 2000 2500 3000 3500 40000
50
100
150
200
250
300
3438.90
% T
Wavelength (cm-1)
vi SnO NP (8000C)
v SnO NP (6000C)
iv SnO NP (4000C)
iii SnO NP (2000C)
ii SnO NP
i SnCl2.2H
2O
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ESI 9.
Nitrogen adsorption–desorption isotherm and the BJH pore size distribution of SnO
nanoplates
The N2 adsorption–desorption isotherm and the pore size distribution of SnO nanoplates.
The BET specific surface area of the SnO plates is found to be 2.99 m2/g.
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ESI 10.
HRTEM image of SnO sample annealed at 200°C. A polycrystalline SnO2
nanoparticles are formed on the surface of SnO.
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ESI 11:
Morphplogy SnO nanoplates at different temperature
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ESI 12:
Photodegradation experiment
To carry out the photoreaction, one 100 mL capacity photoreactor was used. The
photoreactor was kept at 30ºC circulating cold water during the photoreaction to avoid
heating effect on the reaction mixture. Reaction mixture was prepared in the photoreactor
using 0.025 g of the as prepared SnO powder and 50 mL aqueous solution of MB so that
the final concentration of MB becomes 3 × 10-5
M. The MB solution was allowed to
stand for 2 h for aging to reach an adsorption-desorption equilibrium on the surface of
SnO before light irradiation. We have used commercial visible light source (i.e. 200 W
and 500 W tugsten light) and commercial UV-light source (365 nm). The reaction
mixture was well stirred at 500 rpm during photoreaction due to passing of air O2 into the
reaction mixture.
The time dependent photocatalytic reaction was monitored spectrophotometrically.
During the absorption measurement of the reaction mixture containing the exposed dye
solution and SnO material, methylene blue solution was separated by centrifugation
(5000 rpm for 10 min) to avoid light scattering due to the dispersed SnO nanocrystals in
the aqueous phase. In the similar fashion, we have also used annealed tin oxide samples
for photodegradation of methylene blue by UV-light (365 nm)
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ESI 13.
Photocatalytic degradation of MB on SnO nanoplates in presence of visible light
(tungsten light 200 W) (a), UVlight (365 nm) (b), and in the dark condition (c)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
2.5
max=662 nm
SnO
Visible light
a
Initial conc.
Adsorption
0 h
4
8
12
16
20 h
Ab
so
rpti
on
(a
.u.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
max= 662 nm(b)
SnO
UV-Light
initial
0
4
6
9
12
15
18 h
Ab
so
rpti
on
(a.u
.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
Dark condition Initial
adsorption (2 hr)
4 hr
8 hr
20 hr
c max
= 662 nm
Ab
so
rba
nc
e (
a.u
.)
Wavelength (nm)
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ESI 14. Photocatalytic degradation of MB in presence of tin oxide
nanoplates under different visible lights
400 500 600 700 8000.0
0.5
1.0
1.5
2.0
2.5
Visible Light
Tugsten bulb 200 W
(a)
max= 662 nm
Initial conc.
Adsorption
0 h
4
8
12
16
20 hAb
so
rpti
on
(a.u
.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
2.5
max= 662 nm(b)
Visible Light
(500 W tugsten bulb)Initial
2 hrs adsorption
0 hrs
3 hrs
6 hrs
9 hrs
12 hrs
15 hrs
18 hrs
Ab
so
rba
nc
e (
a.u
.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
max= 662 nm
(c)
Visible Sun LightInitial
2 hrs adsorption
0 hrs
4 hrs
6 hrs
8 hrs
10 hrs
Ab
so
rban
ce (
a.u
.)
Wavelength (nm)
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ESI 15. Photocatalytic degradation of MB (3 × 10-5
M) in presence of
annealed tin oxide samples (0.025 g) by UV-light (365 nm): SnO at 200°C
(a), SnO at 400°C (b), SnO at 600°C (c) and SnO at 800° C (d).
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
max= 662 nm
(a)
Initail
Adsorption
3
6
9
12
15 hr
Ab
so
rpti
on
(a.u
.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0
Initail
Adsorption
3
6
9
12
15 hr
(c)
max= 662 nm
Ab
so
rpti
on
(a.u
.)
Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0 (b)
Initail
Adsorption
3
6
9
12
15 hr
max
=622 nm
Ab
so
rpti
on
(a.u
.)Wavelength (nm)
400 500 600 700 800 9000.0
0.5
1.0
1.5
2.0 (d) max
= 662 nm
Initail
Adsorption
3
6
9
12
15 hr
Ab
so
rpti
on
(a.u
.)
Wavelength (nm)
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ESI 16. Nitrogen adsorption–desorption isotherm for the SnO at 200°C (a),
SnO at 400°C (b), SnO at 600°C (c) and SnO at 800°C and their
comparative BET surface area and pore volume.
The BET surface area of the annealed SnO sample (at 200°C, 400°C, 600°C and 800°C)
is changed and the result is tabulated as bellow.
Annealed SnO
Sample
BET surface Area
(m2/g)
SnO (200°C) 2.85
SnO (400°C) 2.194
SnO (600°C) 3.816
SnO (800°C) 1.133
0.0 0.2 0.4 0.6 0.8 1.0
0
2
4
6
8
10
12
14
(b)
Desorption
Adsorption
Vo
lum
e [
cc/g
]
Relative Pressure, P/P0
0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
25
(c)
Desorption
Adsorption
Vo
lum
e [
cc/g
]
Relative Pressure P/P0
0.0 0.2 0.4 0.6 0.8 1.0
0
1
2
3
4
5
6
7
8
Desorption
Adsorption
(d)V
olu
me [
cc/g
]
Relative Pressure P/P0
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Desorption
Adsorption
(a)
Vo
lum
e [
cc
/g]
Relative Pressure P/P0
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ESI 17: Determination of VB position of SnO and SnO2 from the survey
scan of SnO and SnO2 material.
0 10 20 30 40500
1000
1500
2000
2500
3000
3500
4000
4500
SnO2
VB Position = 8.1 eV
(b)
Inte
nsit
y (
a.u
.)
Binding Energy (eV)
0 10 20 30 40
600
1200
1800
2400
3000
3600
4200 (a)
SnO
VB Position = 5.88 eV
Inte
nsit
y (
a.u
.)
Binding Energy (eV)
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