Hierarchical assemblies of CdxZn1-xS complex architectures and their enhanced visible-light photocatalytic activities for H2-production

Article abstract of DOI:10.1016/j.jallcom.2013.07.013

The shape-controlled synthesis of hierarchically micro- and nanostructured materials has opened up new opportunities to improve their properties. In this work, Cd_xZn_1xS complex architectures, such as microflowers and microspheres, were prepared through a facile solvothermal method, by using diethylenetriamine (DETA) and water as solvent. Within the Zn content increase from 0.2 to 0.8 in the Cd_xZn_{1 x}S solid solution, the morphology transformed progressively from microflowers agglomerates to microspheres. The photocatalytic H₂ evolution over the solid solutions was further investigated through the H ₂ evolution from aqueous solutions containing S^2-/SO ^2-₃, and the highest H₂ evolution rate without co-catalysts even reached 1.8 mmol g¹ h¹. The reasons for the difference in the photocatalytic properties of these Cd_xZn _1xS architectures were also investigated. The morphology change of Cd_xZn_1xS solid solution leads to different BET and surface defects, finally resulting in the variation of photocatalytic activity.

Full text of DOI:10.1016/j.jallcom.2013.07.013

Journal of Alloys and Compounds 578 (2013) 571–576
Contents lists available at SciVerse ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
Hierarchical assemblies of Cd Zn S complex architectures and their
x
1ꢀx
enhanced visible-light photocatalytic activities for H -production
2
Jian Wang a,b, Bo Li a,c, Jiazang Chen a,b, Li Li , Jianghong Zhao , Zhenping Zhu
a
a
a,
⇑
a
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taoyuan South Road 27, Taiyuan, 030001 Shanxi, People’s Republic of China
University of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, People’s Republic of China
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 April 2013
Received in revised form 1 July 2013
Accepted 2 July 2013
Available online 11 July 2013
The shape-controlled synthesis of hierarchically micro- and nanostructured materials has opened up new
opportunities to improve their properties. In this work, Cd
flowers and microspheres, were prepared through a facile solvothermal method, by using diethylenetri-
amine (DETA) and water as solvent. Within the Zn content increase from 0.2 to 0.8 in the Cd Zn1ꢀxS solid
solution, the morphology transformed progressively from microflowers agglomerates to microspheres.
The photocatalytic H evolution over the solid solutions was further investigated through the H evolu-
tion from aqueous solutions containing S =SO3 , and the highest H evolution rate without co-catalysts
. The reasons for the difference in the photocatalytic properties of these
Zn1ꢀxS architectures were also investigated. The morphology change of Cd Zn1ꢀxS solid solution leads
x
Zn1ꢀxS complex architectures, such as micro-
x
2
2
Keywords:
Cd Zn1ꢀxS
x
Hierarchical architectures
Photocatalytic
2ꢀ
2ꢀ
2
ꢀ1
ꢀ1
even reached 1.8 mmol g
Cd
h
x
x
Hydrogen evolution
to different BET and surface defects, finally resulting in the variation of photocatalytic activity.
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
photocatalytic activity, it is very important to synthesize the nano-
x
crystals with a specific size and morphology. To date, Cd Zn1ꢀxS
Since the pioneering work by Fujishima and Honda, heteroge-
compounds with different morphologies, including nanoparticles
[12] and rod-like nanostructures [13,14], have been prepared and
used as catalysts in photocatalytic systems. And it has been found
neous photocatalytic water splitting over inorganic semiconductor
catalysts for H evolution has attracted considerable attention [1].
2
However, most of the developed photocatalyst with wide band gap
can only absorb the ultraviolet light. To maximize the use of solar
energy, visible light-responsive semiconductor photocatalysts
should be developed [2–4]. As an important semiconductor, cad-
mium sulfide (CdS) nanocrystals has the narrow band-gap
2
that these photocatalysts have better photocatalytic H -production
activities. Recently, some hierarchical micro- and nanostructured
materials composed of nanosized building blocks such as nanopar-
ticles or nanorods have been prepared and found to have new
properties and exhibit potential applications in photocatalytic
(
Eg = 2.4 eV) and valence bands at relatively negative potentials,
fields [15–17]. For example, some semiconductors such as Fe
2 3
O
which make it suitable for hydrogen production under visible light
in the presence of sacrifice agents [5–7]. Nevertheless, the photo-
catalytic efficiency of CdS for water splitting is still limited, it is
necessary to find suitable method for its structure modification.
One strategy is to incorporate of ZnS into the structure of CdS for
[18], ZnO [19], and TiO [20] with a hierarchical structure were
2
successfully synthesized and exhibited well photocatalytic proper-
ties. However, there is no research on the photocatalytic water
splitting for hydrogen production by using the complex hierarchi-
cal Cd
x
Zn1ꢀxS micro- and nanostructure.
Zn1ꢀxS solid solutions with
forming the series of Cd
x
Zn1ꢀxS solid solution with adjustable
In the current study, a series of Cd
x
band-gap [8,9], its conduction band and valence band can shift to
more positive and negative position, leading to the increment of
photocatalytic properties [10,11].
It is well known that the applications for materials depend
critically on their properties such as the crystal structure, size,
shape, specific area and surface defect states. For improving the
hierarchical structures have been efficiently synthesized in a DETA
aqueous solution through a one-step mix-solvothermal method.
The photocatalytic performance was then evaluated through the
2
ꢀ
2ꢀ
H
2
evolution from aqueous solutions containing S =SO3 under
visible light irradiation (k > 420 nm). The Cd0.2Zn0.8S microspheres
exhibited the best photocatalytic activity with H production rate
, probably resulted from the needful surface
area and surface defect. After loading 1 wt.% Pt on the surface of
Cd0.2Zn0.8S, the rate of production even can reach
2
ꢀ1
ꢀ1
of ca.1.8 mmol g
h
⇑
Corresponding author. Tel./fax: +86 351 4048433.
E-mail address: zpzhu@sxicc.ac.cn (Z. Zhu).
H
2
ꢀ1
ꢀ1
5 mmol g
h .
0
925-8388/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jallcom.2013.07.013

5
72
J. Wang et al. / Journal of Alloys and Compounds 578 (2013) 571–576
1.0
0.8
0.6
0.4
0.2
a
c
d
e
f
0.0
0.2
f
b
-
e
d
2.0
2.5
3.0
3.5
4.0
4.5
5.0
d
e
hν/ev
f
c
b
b
c
a
a
20
30
40
50
60
70
2
θ (degree)
300
400
500
600
700
wavelength (nm)
x
Fig. 1. The XRD pattern for Cd Zn1ꢀxS nanocrystals: (a) ZnS (b) Cd0.2Zn0.8S (c) Cd0.4
Zn0.6S (d) Cd0.6Zn0.4S (e) Cd0.8Zn0.2S and (f) CdS.
Fig. 2. The UV–Vis spectrum for Cd
x
Zn1ꢀxS nanocrystals: (a) ZnS (b) Cd0.2Zn0.8S (c)
Cd0.4Zn0.6S (d) Cd0.6Zn0.4S (e) Cd0.8Zn0.2S and (f) CdS.
2
. Experimental
2
.1. Cd Zn1ꢀxS nanocrystal syntheses
x
The chemicals used in this study were all analytical reagent grade and used
without further purification. The Cd Zn1ꢀxS nanocrystals were prepared through a
solvothermal route. First, a suitable amount of Cd(CH COOH) O and Zn(CH3-
ꢁ2H
O (total amount of Cd and Zn = 10 mmol) and 20 mmol thiourea
x
3
2
2
2
+
2+
COOH)
2
ꢁ2H
2
were dissolved in 24 mL deionized water. DETA (12 mL) was then added into the
aqueous solution. The mixture was stirred to form a homogeneous solution and
placed in an autoclave with an inner Teflon lining (the volume is 50 mL). Then
the autoclaves were maintained at 180 °C for 12 h and cooled to room temperature.
Finally, the product was filtered, washed several times with distilled water and eth-
anol, and dried in a vacuum oven at 60 °C for 12 h.
2.2. Characterization
The X-ray diffraction (XRD) patterns were obtained using a Bruker D8 Advance
X-ray diffractometer (Germany) with Cu Ka radiation. The UV–Vis absorption spec-
tra were obtained using a Shimadzu UV–Vis–NIR spectrophotometer (UV-3600, Ja-
pan). Photoluminescence (PL) spectra were recorded at room temperature on a
fluorescence spectrophotometer (Hitachi F-7000, Japan) using Xenon lamps as the
excitation source, all samples were excited using a wavelength of 300 nm. Scanning
electron microscopy (SEM) was conducted using a LEO-438VP field emission scan-
ning electron microscope (Germany). Transmission electron microscopy (TEM) was
performed using a JEM-2100 transmission electron microscope (Japan) using a
x 1ꢀx
Fig. 3. The PL spectrum for Cd Zn S nanocrystals.
3. Results and discussion
.1. Formation of Cd Zn1ꢀxS solid solutions
XRD was used to characterize the phase structure of the sam-
3
x
2
00 kV accelerating voltage. The Brunauer–Emmett–Teller (BET) surface area were
measured by a nitrogen adsorption technique at 77 K using an ASAP2020M auto-
mated gas-sorption system (America).
ples. From the Fig. 1, the patterns for CdS and ZnS match well with
the standard spectra (JCPDS 41-1049 and 36-1450, respectively).
And all of the samples exhibits a pure hexagonal wurtzite struc-
ture, with the prominent diffraction peaks corresponding to
2 x
2.3. Photocatalytic H production on the Cd Zn1ꢀxS solid solution
(
100), (002), (101), (110), (103) and (112) planes. Due to the
The photocatalytic reaction was conducted in a closed glass circulation system.
The Cd Zn1ꢀxS photocatalyst (0.1 g) was dispersed in a 100 mL aqueous solution
containing 0.1 M Na S and 0.1 M Na SO , which served as sacrificial agents. Pt
was in situ photodeposited from the H PtCl O precursor to act as a co-catalyst
ꢁ6H
for the promotion of H evolution. The entire reaction process was irradiated using
a 300 W Xe lamp (Trusttech PLS-300UV, China) with a cutoff filter (k P 420 nm).
The amount of H evolved was determined using an online thermal conductivity
smaller Zn atomic radius than Cd atomic radius, the zinc atoms
into CdS crystal cell can form infinite solid solution. And it has been
proved that the diffraction peaks of Cd Zn S solid solution can
x 1ꢀx
shift to lower angles as the value of x in the Cd Zn1ꢀxS solid solu-
x
tion increases [12,13]. In our experimental, the diffraction peak
x
2
2
3
2
6
2
2
2
also changes with different Cd and Zn composition, indicating
detector (TCD) gas chromatograph with Ar as the carrier gas.
Table 1
The lattice constants and band gap of Cd
x
Zn1ꢀxS solid solution.
Catalyst
CdS
Cd0.8Zn0.2
S
Cd0.6Zn0.4
S
Cd0.4Zn0.6
S
Cd0.2Zn0.8
S
ZnS
Lattice
Constants
Band gap (eV)
a (Å)
c (Å)
4.1187
6.6868
2.11
4.0916
6.6674
2.21
4.0625
6.6426
2.29
4.0525
6.6194
2.37
4.0439
6.5804
2.45
3.7826
6.5526
3.45

J. Wang et al. / Journal of Alloys and Compounds 578 (2013) 571–576
573
x
Fig. 4. The scanning electron microscopy of Cd Zn1ꢀxS nanocrystals: (a) ZnS (b) Cd0.2Zn0.8S (c) Cd0.4Zn0.6S (d) Cd0.6Zn0.4S (e) Cd0.8Zn0.2S and (f) CdS.
the successful synthesis of Cd
constants a and c for hexagonal phase of Cd
was calculated using the following equation:
x
Zn1ꢀxS solid solution. The lattice
Zn1ꢀxS solid solutions
an excitation wavelength of 280 nm. It can be found the ZnS has
a strong broad emission at 428 nm. Similarly, the PL spectrum of
CdS also has a strong emission at 581 nm. The near band edge
x
(
NBE) emissions of both ZnS and CdS do not correspond to their
!
2
2
2
1
4
3
h þ hk þ k
l
absorption wavelength, inferring that the PL is commonly attrib-
uted to the recombination of the charge carriers within the surface
states. And for the Cd Zn1ꢀxS solid solution, it can also be specu-
x
¼
þ
c
2
2
2
a
d
The calculated lattice constants a and c are listed in Table 1. The
changes of lattice constants also demonstrate the formation of so-
lid solutions.
lated from the PL spectrum that the luminescence emissions are
similarly derived from the surface defect states. Moreover, the
intensity of the strongest emission peak increases as Zn compo-
nent, suggesting the increases of surface defects.
x
The UV–Vis absorption spectra of the Cd Zn1ꢀxS solid solutions
with different Cd concentrations are shown in Fig. 2. The absorp-
tion edge of ZnS is approximately 370 nm, but the other samples
exhibit intense absorption bands with steep edges in the visible
x
3.2. Cd Zn1ꢀxS alloy nanocrystal morphology
light region. In addition, the absorption edge of the Cd
x
Zn1ꢀxS solid
Since preparing the materials in nanoscale dimension is one of
the significant methods to improve the photocatalytic activity, the
solution gradually red-shifts as the amount of Cd increase. This
phenomenon can be attributed to a band transition rather than a
transition from impurity levels, indicating the formation of the Cdx-
Zn1ꢀxS solid solution. In view of the direct band gap nature of Cdx-
morphology of Cd
Fig. 4 shows the SEM images of the synthesized Cd
x
Zn1ꢀxS was investigated through SEM and TEM.
Zn1ꢀxS samples.
x
The pure ZnS nanocrystals clearly consist of microspheres which
were stacked by short nanorods. Under solvothermal conditions,
the structures and morphologies of ZnS nanostructures have been
studied in DETA or in an aqueous DETA solution [21]. With the in-
creases of water and decreases of DETA, the morphologies of ZnS
will transfer from nanosheets to microsphere. In our experimental,
the volume of water and DETA is 2:1; the synthetic ZnS micro-
spheres conformed to this rule. However, the morphologies of
CdS were microflowers that assembled from nonorods. CdS micro-
flowers can also be produced in a mixed solution of DETA and
deionized water via a facile solvothermal approach [22]. With
decreasing the volume of DETA and water, the CdS microflowers
would be formed. In our experimental, the morphologies of CdS
may be associated with it. As the solid solution is formed, the
Zn1ꢀxS, the relation between the absorption coefficient (
incident photon energy (h ) can be written as = C(h
ꢀ Eg)
where C is a constant and Eg is the direct band gap. Hence, the
band gap value of Cd Zn1ꢀxS architectures can be obtained through
extrapolating the linear part of the (h
Inset Fig. 2). The specific band gap data can be shown in Table 1.
a) and
1
/2
m
ahm
m
,
x
2
2
m
)–(ahm) plot to (ahm) = 0
(
The band gap for CdS is a little lower than the reported data (Eg of
ca. 2.47 eV) and the reason may be that the aggregation in the
sample results in large particle sizes, leading to enhanced light
harvesting and red-shifted light absorption.
For the further study of the optical properties samples, photolu-
minescence (PL) measurement was measured at room tempera-
x
ture. Fig. 3 shows the PL spectrum of Cd Zn1ꢀxS solid solution at

5
74
J. Wang et al. / Journal of Alloys and Compounds 578 (2013) 571–576
formed nanocrystals with different morphologies that depend on
the Zn content of the solid solutions. The nanocrystals made of
microflowers have a low Zn content (x = 0.2 or 0.4), but the micro-
spheres would be found in the high Zn content (x = 0.2 or 0.4) sam-
a
ples. Similar Cd
x
Zn1ꢀxS nanocrystls have been prepared by using
S as sulfur source in a mixed solution of DETA and water
23]. The possible reason for the morphology change may be the
(
[
4 2
NH )
2
+
2+
2+
2ꢀ
difference of the M ion (M = Zn or Cd ) reactivity with S
,
which follows the order, Cd2 > Zn . More the detailed is needed
+
2+
further investigation. The morphologies of Cd Zn1ꢀxS solid solution
x
was also characterized by TEM (shown in Fig. S1), the similar mor-
phology change rule can be associated to the SEM results.
In order to further analyze the basic assembled units, the Cd0.2-
Zn0.8S sample was taken as an example to do HRTEM and selected-
area electron diffraction (SAED) characterization. Fig. S2a shows
x
the HRTEM images of the synthesized Cd Zn1ꢀxS samples, the clear
lattice fringe indicates the products have high crystallization and
single crystal properties. And the clear-cut 0.33 nm lattice spacing
can be corresponding to the wurtzite (002) plane. Some structural
deformations are also found in the HRTEM which can be duo to the
elemental default or asymmetric doping. The corresponding se-
lected-area electron diffraction (SAED, Fig. S2b) pattern indicates
that the typical Cd0.2Zn0.8S sample has a hexagonal single-crystal
structure. These results show that Cd0.2Zn0.8S preferentially grew
along the h001i direction.
5
000
b
4000
3000
2000
1000
0
x
3.3. Photocatalytic performance of the Cd Zn1ꢀxS solid solution
The photocatalytic performance of the Cd
in H production was investigated in a system consisting of 0.1 M
x
Na S/aqueous Na SO solution. Fig. 5a shows that all the Cd Zn1ꢀxS
x
Zn1ꢀxS solid solution
2
2
2
3
0
.0
0.2
0.4
0.6
0.8
1.0
1.2
photocatalysts exhibit high activities than that of ZnS and CdS,
The Cd content in Cd Zn1-xS solid slution (wt %)
indicating that the formation and composition of the solid solution
x
is significant for H
sphere exhibits the best activity among the Cd
tions, with a H
production rate of ꢂ1.8 mmol g
almost 30 times higher than that of CdS. Moreover, the rate of H
production for Cd Zn1ꢀxS decreases as the Cd concentration in
2
production. In particular, the Cd0.2Zn0.8S micro-
Fig. 5. (a) Hydrogen evolution of different Cd
in Na SO and Na
with a cutoff filter (k P 420 nm)) (b) Hydrogen evolution of different Cd
loading with 1 wt.% Pt as co-catalyst in Na SO and Na S aqueous solutions.
x
Zn1ꢀxS solid solution photocatalysts
2
S aqueous solutions (Catalyst: 0.1 g, light source: 300 W Xe lamp
x
Zn1ꢀxS solid solu-
ꢀ
1
ꢀ1
2
3
2
h , which is
x
Zn1ꢀxS
2
2
3
2
x
the solid solution increases, suggesting the composition for solid
solution has an important impact on the photocatalytic activities.
In the same test conditions, the photocayalytic H
2
-production
When photons with sufficient energy strike the semiconductor
photocatalyst, they create pairs of electrons and holes, then the
electron–hole pairs would be separated, transferred into the sur-
face of catalyst and reacted with water, so the surface properties
such as BET surface areas and surface defects have an great effect
on the photocatalytic activities. In general, the bigger the specific
area of semiconductor, the more of active sits with reactants,
which is helpful for photocatalytic reaction. Conversely, it is unfa-
vorable to the photocatalytic reaction. At the same time, the sur-
face defects also have important influence on the catalytic
activity. The suitable surface defects have a help to capture photo-
generated electronic or hole, leading more electron or hole to mi-
grate to the surface of the catalyst for photocatalytic reaction.
activity of hierarchical Cd Zn1ꢀxS complex architectures is better
x
than the reported nanoparticles [24–27].
During the photocatalytic water splitting process, co-catalysts
like noble metals are often needed to promote the separation of
photogenerated carriers and provide low activation potentials for
H
2
evolution, thus serving as active sites for H
2
production. For
the CdS and Cd Zn1ꢀxS solid solution photocatalyst, noble metal
x
such as Pt, Pd and Rh were studied as co-catalysts to enhance the
photocatalytic activity, and Pt has showed the most favorable ef-
fect on the improvement of CdS photocatalytic activity. When Pt
is loaded into the Cd
activity further increases. The rate of H
Pt/Cd0.2Zn0.8S photocatalyst reaches as high as ꢂ5 mmol g
Fig. 5b), which is approximately 1.8 times higher than that over
the Cd0.2Zn0.8S solid solution catalyst alone.
The Cd Zn1ꢀxS solid solution with a hexagonal wurtzite phase
often has the best photocatalytic activity when the Zn content
x
Zn1ꢀxS photocatalysts, the photocatalytic
2
evolution over the
ꢀ1
ꢀ1
h
x
The synthetic hierarchical assemblies of Cd Zn1ꢀxS complex
(
architectures have different morphology. In particular, the mor-
phology changes from microflowers agglomerates to microspheres
with the Cd content in the solid solution, which may generate
x
x
changes of surface properties. Firstly, the BET of Cd Zn1ꢀxS solid
(
1ꢀx) is approximately 0.6–0.7, which may be attributed to the
solution has been changed. As shown in Table 2, the ZnS has a rel-
2
suitable band gap and negative shift of the conduction band. In
the current results, the Cd0.4Zn0.6S solid solution gives a very high
atively high BET data (ꢂ40m /g), and the CdS exhibits low surface
2
area, only 7 m /g. For the different constituent solid solution, the
ꢀ1
ꢀ1
rate of H
of the aforementioned reason. However, the Cd0.2Zn0.8S solid solu-
tion exhibits the best photoactivity for H production. Therefore,
aside from the band-gap structure for the hierarchical Cd
solid solution, other influence factors should be considered.
2
production (ꢂ0.8 mmol g
h
), most probably because
BET data will increase with the Cd content decrease, and the Cd0.2-
2
Zn0.8S microsphere especially has a higher BET results (ꢂ42 m /g).
2
Apparently, the higher BET is in favor of providing more reaction
site, causing the enhancement of photocatalytic activity. In addi-
x
Zn1ꢀxS
x
tion, the change of Cd Zn1ꢀxS morphologies is also possible for

J. Wang et al. / Journal of Alloys and Compounds 578 (2013) 571–576
575
2
3
ꢀ
2ꢀ
Table 2
The BET of Cd
was evacuated after each run. By combination of SO and S uti-
x
Zn1ꢀxS solid solution.
CdS Cd0.8Zn0.2
22
lized as sacrificial agent, different reactions occurred for the photo-
excited holes as follows:
Catalyst
S
Cd0.6Zn0.4
26
S
Cd0.4Zn0.6
36
S
Cd0.2Zn0.8
42
S
ZnS
40
2
BET (m /g)
7
Cd
x
Zn1ꢀxS þ h
m
! hþ þ eꢀ
ꢀ
ꢀ
2
e
þ 2H
2
O ! H
2
þ 2OH
SO þ 2OH þ 2h ! SO4 þ 2Hþ
2
3
ꢀ
ꢀ
þ
2ꢀ
2
ꢀ
þ
2ꢀ
2S
þ 2h ! S2
2
ꢀ
2ꢀ
2ꢀ
þ S2ꢀ
S
þ SO3 ! S
2
O
þ
2
3
2
ꢀ
2ꢀ
2ꢀ
SO þ S þ 2h ! S
2
O
3
3
Therefore, no significant decrease in the photocatalytic activity
is observed, the hydrogen evolution rate still reached and
ꢀ1
ꢀ1
1
.6 mmol g
. Conclusions
A series of hierarchical Cd
h
in the fourth reaction run.
4
x
Zn1ꢀxS micro- and nanostructure
have been synthesized in a DETA and water solution using the
solvothermal method. The morphology of the nanoflowers was
characterized. Within the Zn content increase from 0.2 to 0.8 in
the Cd
sively from microflowers agglomerates to microspheres. Further-
more, the photocatalytic performance of the Cd
nanoflowers in H evolution was investigated. The Cd0.2Zn0.8S solid
solution composed of thin slices exhibited the best photocatalytic
x
Zn1ꢀxS solid solution, the morphology transformed progres-
x
Fig. 6. Schematic illustration of Cd Zn1ꢀxS in photocatalytic processes.
x
Zn1ꢀxS
2
ꢀ1
ꢀ1
activity for H
2
evolution, with an initial rate of 1.8 mmol g
h .
This high activity may be due to the specific morphology which
has a relatively high BET and surface defects, leading to a high
number of reaction sites.
Acknowledgments
The authors are grateful for the financial support of the Knowl-
edge Innovation Project of Chinese Academy of Sciences (No.
KJCX2.YW.M10).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jallcom.2013.
0
7.013.
2
Fig. 7. Amounts of H evolution according to reaction time of Cd0.2Zn0.8S.
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3