Cu2ZnI4/ZnO nanocomposites: In-situ synthesis, characterization and optical properties

Article abstract of DOI:10.1016/j.molliq.2016.07.078

In this work, copper zinc tetraiodide/zinc oxide (Cu₂ZnI₄/ZnO) nanocomposites were successfully synthesized by simple solid-state method. The effect of various parameters such as Cu⁺/Zn^+?2 molar ratio, time and temperature of reaction on morphology, size and purity of products was investigated. The as-prepared products were characterized by X-ray diffraction (XRD), field emission scanning and transmittance electron microscopy (FESEM, TEM), and X-ray energy dispersive spectroscopy (EDS) analysis. Application of Cu₂ZnI₄/ZnO nanocomposite as photocatalyst was confirmed by the band gap estimated through UV–vis spectroscopy. To investigate the photocatalytic properties of this product, photooxidation of methyl orange (MO) was performed. The photocatalytic test shows that the methyl orange degradation was about 54.2% under UV irradiation for 90?min.

Full text of DOI:10.1016/j.molliq.2016.07.078

Journal of Molecular Liquids 222 (2016) 435–440
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Cu2ZnI4/ZnO nanocomposites: In-situ synthesis, characterization and
optical properties
⁎
Fariba Razi, Faezeh Soofivand, Masoud Salavati-Niasari
Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box. 87317-51167, Islamic Republic of Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 June 2016
Received in revised form 16 July 2016
Accepted 18 July 2016
Available online 20 July 2016
In this work, copper zinc tetraiodide/zinc oxide (Cu2ZnI4/ZnO) nanocomposites were successfully synthesized by
simple solid-state method. The effect of various parameters such as Cu+/Zn+2 molar ratio, time and temperature
of reaction on morphology, size and purity of products was investigated. The as-prepared products were charac-
terized by X-ray diffraction (XRD), field emission scanning and transmittance electron microscopy (FESEM,
TEM), and X-ray energy dispersive spectroscopy (EDS) analysis. Application of Cu2ZnI4/ZnO nanocomposite as
photocatalyst was confirmed by the band gap estimated through UV–vis spectroscopy. To investigate the photo-
catalytic properties of this product, photooxidation of methyl orange (MO) was performed. The photocatalytic
test shows that the methyl orange degradation was about 54.2% under UV irradiation for 90 min.
© 2016 Elsevier B.V. All rights reserved.
Keywords:
Cu2ZnI4
Superionic conductors
Thermal-treatment
Photocatalyst
Nanocomposite
1. Introduction
Chromic compounds have various sub-sets such as: photochromic,
thermochromic and piezochromic compounds. Stimuli of these com-
Nanomaterials have unique properties and many applications in var-
ious fields, so the scientists have focused on investigation of these mate-
rials. Nowadays, nanotechnology has considered as a manufacturing
engineering that can be used to form materials with desired properties.
Nanotechnology has been defined as the design, characterization, pro-
duction, and application of structures, devices and systems by control-
ling shape and size at nanometer scale [1] and preparation of new
compounds such as: nanocomposites and multi-component com-
pounds [2–4]. Composites are compounds that are made from two or
more constituent that their characteristics are different from the indi-
vidual components. Material scientists and engineers have attracted
much attention to nanocomposites due to their fascinating properties.
Nanocomposites demonstrate good advantages over conventional ma-
terials and have many applications in various fields [5–7]. M2NI4 com-
pounds are examples of multi-component compounds that are
classified in two groups: smart materials and superionic conductors
[8–10].
pounds can be light, temperature, change of applied pressure, but all
of their response is color change, reversibly [12]. Recently, superior at-
tention is fascinated to thermochromic compounds because of their
commercial applications and their role in improving temperature indi-
cators and recording devices. On the other hand, M2HgI4 compounds
(M = 1/2 Pb+2, Ag+, Cu+) are a class of thermochromic materials
that their phase and color change at a certain temperature [13]. Chang-
ing phase cause to change ionic conductivity in these compounds, on
the other word, these compounds can be classified in superionic con-
ductors that exhibit exceptionally high values of ionic conductivity
within the solid state [14]. Superionic compounds are solid state
fast ion conductors that can be used as solid-state electrolytes in solid-
state batteries, solar and fuel cells. The structure of these compounds
before temperature of the phase transition is as follows: the
iodide form a face-centered cubic (fcc) lattice that 75% of its tetrahedral
sites are occupied by two one-valance cations and one two-valance
cation and 25% of its tetrahedral sites remain empty, but at above
phase transition temperature three cations are disturbed among the
four tetrahedral sites provided by the fcc sub-lattice of the iodide,
randomly [15].
Smart materials are compounds that can respond to environmental
changes and its one or more properties can be changed. These materials
can be called by type of environmental stimuli and its response
to related stimuli, so there are different types of smart materials such
as shape-memory alloy, piezoelectric, and chromic materials [11].
The M2NI4 compounds, which M = Ag+, Cu+, N = Cd+2, Hg+2
,
Pb+2 have been widely studied [13–16], but the studies on Cu2ZnI4 is
less. In this work, Cu2ZnI4/ZnO nanocomposite was prepared by a sim-
ple thermal-treatment method. The effect of various parameters such
as molar ratio of Cu+ to Zn+2, temperature and time reaction on purity,
morphology, size, and size distribution of products were investigated.
⁎
Corresponding author.
E-mail address: Salavati@kashanu.ac.ir (M. Salavati-Niasari).
http://dx.doi.org/10.1016/j.molliq.2016.07.078
0167-7322/© 2016 Elsevier B.V. All rights reserved.

436
F. Razi et al. / Journal of Molecular Liquids 222 (2016) 435–440
The obtained products were characterized by X-ray diffraction (XRD),
scanning and transmittance electron microscopy (SEM, TEM), and X-ray
energy dispersive spectroscopy (EDS) analysis.
2. Experimental
All the chemicals reagents used in our experiments were of analyti-
cal grade and were used as received without further purification.
Zn(NO3)2·6H2O, CuSO4·5H2O, NaHSO3, and LiI·2H2O were purchased
from Merck. GC-2550TG (Teif Gostar Faraz Company, Iran) were used
for all chemical analyses. The XRD of products was recorded by a Rigaku
D-max C III XRD using Ni-filtered Cu Kα radiation. SEM images were ob-
tained on Philips XL-30ESEM equipped with an energy dispersive X-ray
spectroscopy. The EDS analysis with 20 kV accelerated voltage was
done.
At the first, tan precipitation of CuI was prepared from 0.1 g
CuSO4·5H2O, 0.1 g NaHSO3 and 0.07 g LiI·2H2O in 75 ml of
distilled water. Then, white precipitation of ZnI2 was formed from
Zn(NO3)2·6H2O with stoichiometric amount from LiI·2H2O (by consid-
ering the molar ratio of Cu+ to Zn+2 in various experiments; the
amounts of Zn(NO3)2·6H2O to prepare ZnI2 was changed from 0.07 g
to 0.05 g). Finally, CuI was added to ZnI2, and then the mixture was
grinded and was heated to 160, 180, and 200 °C for 24, 18, and 12 h in dif-
ferent experiments. The various experiments were applied to find the op-
timum condition; details of experiments were illustrated in Table 1.
3. Results and discussion
Fig. 1(a)–(c) illustrates SEM images of samples 1–3, respectively.
The fine and isolated particles and some of the aggregated structures
are related to sample 1 (Fig. 1(a). SEM of sample 2 was given in
Fig. 1(b), a homogenous and dense basis that filled by different struc-
tures such as capsule-like and particles are shown. In Fig. 1(c) that
depicts SEM image of sample 3, agglomerated nanoparticles with aver-
age size about 50 nm together 100 nm-sized capsule-like nanostruc-
tures are shown.
Fig. 1. XRD patterns of sample no. (a) 1, (b) 2, and (c) 3.
CuI þ ZnI2→Cu2ZnI4
XRD analysis, which is the most useful technique for identification of
crystalline structure, was employed to investigate the prepared sam-
ples. In Fig. 1(a)–(c), the XRD patterns of samples 1–3 are shown. The
diffraction lines of these patterns are attributed to Cu2ZnI4 (JCPDS =
40-1169) and ZnO (80-0075) phases. The formation of ZnO as a second
phase can be explained by a proposed mechanism as follows: ZnI2 read-
ily absorbs water from the atmosphere and transforms to Zn(OH)2. On
the other side, Zn(OH)2 can be transformed to ZnO through thermal
treatment at temperature above 150 °C, so Zn(OH)2 is considered as
an intermediate in this reaction [17]. The intensity of diffraction lines
of ZnO (in samples 1–3 as follows: 1 b 3 b 2 that can be connected to
the molar ratio of Cu + to Zn+2 in these samples). The proposed mech-
anism for formation of products:
The effect of the ratio of Cu+:Zn+2 on the morphology and size of the
products (samples 1–3) was investigated (in three ratios of 1, 0.5, and 2
for sample 1–3, respectively). In Fig. 2(a), the SEM image shows that
sample 1 obtained with the molar ratio of Cu+/Zn+2 = 1, consists of
some structures with average size 100 nm and nanoparticles with diam-
eters about 40 nm. The SEM image of sample 2 is shown in Fig. 2(b), this
image consists of a homogenous and dense basis that filled with differ-
ent structures such as micrometer-sized capsule-like and particles with
various sizes are shown. The SEM images in Fig. 2(c) shows that sample
3, consists of capsule-like structure with average width 100 nm and
length 300 nm, and the aggregated particles with diameters about
60 nm.
For studying the formed phases of sample 4 and 5, the XRD patterns
of these samples are given in Fig. 3(a) and (b). In Fig. 3(a), the diffraction
lines are related to three phases of Cu2ZnI4 (JCPDS = 40-1169), Zn(OH)2
(JCPDS = 41-1359), mainly and ZnO (80-0075) partially. Zn(OH)2 can
be considered as an intermediate of transformation reaction of ZnI2 to
CuðSO4Þ2 ꢀ 5H2O þ LiI ꢀ 2H2O þ NaHSO3→CuI þ By‐products
ZnðNO3Þ2 ꢀ 5H2O þ LiI ꢀ 2H2O→ZnI2 þ LiNO3
Table 1
The preparation conditions of sample no. 1–7.
Sample no.
Cu+:Zn+2 molar ratio
Temperature of reaction (°C)
Time of reaction (h)
The prepared products
1
2
3
4
5
6
7
1: 1
1: 2
2: 1
1: 1
1: 1
1: 1
1: 1
200
200
200
200
200
180
160
24
24
24
18
12
24
24
ZnO, Cu2ZnI4
ZnO, Cu2ZnI4
ZnO, Cu2ZnI4
ZnO, Zn(OH)2, Cu2ZnI4
ZnO, Zn(OH)2, Cu2ZnI4
ZnO, Zn(OH)2, Cu2ZnI4
ZnO, Zn(OH)2, Cu2ZnI4

F. Razi et al. / Journal of Molecular Liquids 222 (2016) 435–440
437
Fig. 2. SEM images of sample no. (a) 1, (b) 2, and (c) 3.
ZnO at a temperature about 200 °C. The presence of Zn(OH)2 in samples
4, 5 and its absence in samples 1–3 can be related to the enough time for
transformation of Zn(OH)2 to ZnO, so the presence of Zn(OH)2 as inter-
mediate product of this reaction (transformation of ZnI2 to ZnO) is
justified.
Next, the effect of time reaction was investigated and experiments
were done at two other times 18, and 12 h. The SEM images of these
products are shown in Fig. 4(a) and (b). In Fig. 4(a), the irregular and
heterogeneous structures are shown that related to sample 4. SEM
image of sample 5 is illustrated in Fig. 4(b), this image consists of
nano-sized particles and capsules-like.
The XRD patterns of sample 6, 7 were given in Fig. 5(a) and (b),
these patterns consist of three phases Cu2ZnI4 (JCPDS = 40-1169),
Zn(OH)2 (JCPDS = 41-1359), and ZnO (JCPDS = 80-0075). As said
above, the presence of Zn(OH)2 as an intermediate in these patterns
is due to the low temperature of reaction. So Zn(OH)2 cannot be
transformed to ZnO, completely and diffraction lines of Zn(OH)2 are
shown in these patterns. The crystallinity of sample 7 is lower than sam-
ple 6, because of the reaction temperature in sample 6 is lower than
sample 7.
In continuation, the effect of temperature on size and morphology of
products was investigated; SEM images of samples 6 and 7 are shown in
Fig. 6(a) and (b), respectively. In Fig. 6(a), the larger structures are
shown that consist of uniform and fine particles with an average size
about 20 nm. The agglomerated nanoparticles with size about 100 nm
were shown in Fig. 6(b) (sample 7). The SEM image of this sample illus-
trates an amorphous basis together with other structures.
By considering all of SEM images and XRD patterns of as-prepared
samples, sample 1 was chosen as desired sample and further analyses
such as EDS, TEM, and UV–vis were applied on this sample, furthermore
application of this sample as a photocatalyst was carried out under UV
irradiation.
Fig. 3. XRD patterns of sample no. (a) 4, (b) 5.

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F. Razi et al. / Journal of Molecular Liquids 222 (2016) 435–440
Fig. 4. SEM images of sample no. (a) 4, (b) 5.
Fig. 6. SEM images of sample no. (a) 6, (b) 7.
The TEM images of the as-prepared Cu2ZnI4/ZnO nanocomposite
are shown in Fig. 7(a), (b), and (c). Fig. 7(a)–(c) depicts TEM
images of the as-prepared Cu2ZnI4/ZnO nanocomposite (sample no. 1)
in various scale 200, 100, and 50 nm, respectively. The average
size of these nanoparticles is about 35 nm. To provide typical
histograms of the particle diameters, the average particle diameter of
the Cu2ZnI4/ZnO nanocomposite was estimated by measuring over
40 particles on the TEM images by using Digimizer software.
As shown in Fig. 7(d), the particle size distribution of sample 1 is ob-
served in the range of 20–100 nm. By considering the particle size distri-
bution of the sample 1 can be said that the average, minimum and
maximum size of particle size are 36.82 nm, 20.99 nm, and 97.33 nm,
respectively.
In The EDS spectrum of as-prepared product from sample 1
(Fig. 8), Cu, Zn, and I elements are detectable. The other peaks were
not detected in this spectrum, so purity of the as-prepared product
was confirmed.
Fig. 9(a) shows the UV–vis absorption spectrum of as-prepared
Cu2ZnI4/ZnO nanocomposite from sample 1. In this spectrum an absorp-
tion peak around approximate 336 nm can be observed. Optical band
gap (Eg) may be evaluated based on the optical absorption spectrum
using the following equation [18–23]: (Ahυ)n = B(hυ − Eg); Where
Fig. 5. XRD patterns of sample no. (a) 6, (b) 7.

F. Razi et al. / Journal of Molecular Liquids 222 (2016) 435–440
439
Fig. 7. TEM images of sample no. 1 at scale (a) 200, (b) 100, (c) 50 nm and (d) particle size distribution of sample no. 1.
hυ is the photon energy, A is absorbent, B is a material constant and n is
2 or 1/2 for direct and indirect transitions, respectively. The optical band
gap for the absorption peak is obtained by extrapolating the linear por-
tion of the (Ahυ)n curve versus hυ to zero. No linear relation was found
for n = 1/2, suggesting that the prepared Cu2ZnI4/ZnO nanocomposite
is semiconductor with direct transition at this energy. The band gap of
as-prepared Cu2ZnI4/ZnO nanocomposite was calculated about 3 eV
(Fig. 9(b). The calculated band gap confirms that this compound can
be used as an effective photocatalyst.
The photocatalytic activity of Cu2ZnI4/ZnO nanocomposite was in-
vestigated by monitoring the degradation of methyl orange (MO) solu-
tion dye under UV light irradiation (Fig. 10). The photocatalytic
degradation reaction was performed out in a quartz photocatalytic reac-
tor and carried out with a 10 ppm MO solution containing 0.05 g of
photocatalyst (Cu2ZnI4 nanoparticles). This mixture was aerated for
30 min to reach adsorption equilibrium. Then, the mixture was placed
inside the photoreactor in which the vessel was 40 cm away from the
UV of 100 W Osram lamp. The quartz vessel and light sources were
placed inside a black box equipped with a fan to prevent UV leakage.
The experiments were performed at room temperature and pH of the
MO solution was adjusted 2–3. The MO degradation percentage was cal-
culated by Eq. (1) as follows:
D:P:ðtÞ ¼ ðA0−AtÞ=A0 ꢁ 100
ð1Þ
where A0 and At are the absorbance value of MO solution at 0 and t min,
respectively [2].
According to photocatalytic calculations by Eq. (1), the MO degrada-
tion percentage was about 54.2% after 90 min irradiation of UV light in
presence Cu2ZnI4 nanoparticles as photocatalyst.
Fig. 8. EDS spectrum of samples no. 1.

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F. Razi et al. / Journal of Molecular Liquids 222 (2016) 435–440
in the desired condition such as TEM, EDS, UV–vis. By considering
band gap estimated through UV–vis spectrum of this product, applica-
tion of Cu2ZnI4/ZnO nanocomposite obtained in this work confirms as
photocatalyst. To investigate the photocatalytic properties of this prod-
uct, photo-oxidation of methyl orange (MO) was performed. The photo-
catalytic test shows that the methyl orange degradation was about
54.2% after 90 min irradiation of UV light.
Acknowledgements
Authors are grateful to the council of Iran National Science Founda-
tion and University of Kashan for supporting this work by Grant No
(159271/576).
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4. Conclusions
In this project, we connect three fascinated fields: photocatalytic ac-
tivity, thermochromic phenomena, and superionic conductivity with
the synthesis of Cu2ZnI4/ZnO nanocomposite. Herein, Cu2ZnI4/ZnO
nanocomposite with average size about 35 nm was synthesized by the
simple thermal-treatment method. The role of various parameters
such as molar ratio of Cu+/Zn+2, time and temperature of the reaction
was investigated on purity, size and morphology of products and opti-
mum condition for preparation of Cu2ZnI4/ZnO nanocomposite was
found. The further analyses were carried out on the product prepared