Structural and thermal characterization of NixZn1?xAl2O4 synthesized by the polymeric precursor method

Article abstract of DOI:10.1007/s10973-015-5056-4

Oxides with Ni_xZn_1?xAl₂O₄ spinel structures (x?=?0, 0.05, 0.10, 0.15 and 1.0) have been synthesized by a simple polymeric precursor method. The samples were calcined at 600, 800 and 1000?°C for 2?h. The thermal decomposition of materials has been investigated by TG and DTA. X-ray diffractogram showed that the synthesis is efficient to produce spinel structures with no significant interfering phases. Materials characterization also revealed that these oxides had surface areas (BET) in the range of 8–156?m²?g^?1. The absorption bands in the infrared spectroscopy (IR) were related to (ZnO₄) and [AlO₆] stretching vibration, and the UV–Vis spectrograms indicated the presence of Ni²⁺ in tetrahedral sites. The colorimetric analysis (CIELab) results showed that the color of the pigments is blue and becomes lighter with increasing synthesis temperature. All these structural and thermal properties indicated that the materials have potential applications as pigments, catalysts and so on.

Full text of DOI:10.1007/s10973-015-5056-4

J Therm Anal Calorim
DOI 10.1007/s10973-015-5056-4
Structural and thermal characterization of Ni Zn Al O
x
12x 2 4
synthesized by the polymeric precursor method
1
2
1
3
Renan M. Queiroz
•
Tiago L. Coelho
1
•
Isabella M. Queiroz
Geraldo N. da Rocha Filho
•
Luiza H. O. Pires
1
•
4
Ieda M. G. Santos
Carlos E. F. da Costa
•
Jos e´ R. Zamian
•
•
1
Received: 30 May 2015 / Accepted: 20 September 2015
Ó Akad e´ miai Kiad o´ , Budapest, Hungary 2015
Abstract Oxides with Ni Zn Al O spinel structures
1-x
Introduction
x
2 4
(
x = 0, 0.05, 0.10, 0.15 and 1.0) have been synthesized by
a simple polymeric precursor method. The samples were
calcined at 600, 800 and 1000 °C for 2 h. The thermal
decomposition of materials has been investigated by TG
and DTA. X-ray diffractogram showed that the synthesis is
efficient to produce spinel structures with no significant
interfering phases. Materials characterization also revealed
that these oxides had surface areas (BET) in the range of
The development of high stable pigments with intense
tonalities has attracted the interest of the ceramic industries
[1, 2]. Mixed metal oxides with a spinel structure (AB O )
2
4
can be considered as a subcategory of complex inorganic
color pigments that show high thermal stability and high
mechanical resistance [3, 4]. Therefore, these oxides can
provide potential ceramic pigments [5], magnetic devices
[6], thin films [7], catalysts and supports for a wide range
of applications [8, 9]. This type of spinel compounds have
also received much attention for their capacity to accom-
modate different cations in their structure, allowing for
several types of doping, and consequently providing a wide
range of colors [10].
2
-1
8
–156 m g . The absorption bands in the infrared spec-
troscopy (IR) were related to (ZnO ) and [AlO ] stretching
4
6
vibration, and the UV–Vis spectrograms indicated the
2
?
presence of Ni
in tetrahedral sites. The colorimetric
analysis (CIELab) results showed that the color of the
pigments is blue and becomes lighter with increasing
synthesis temperature. All these structural and thermal
properties indicated that the materials have potential
applications as pigments, catalysts and so on.
Spinels can be classified into three categories: normal,
?
inverse and intermediate. In the case of normal spinel, A
2
3
ions occupy tetrahedral sites and B ions occupy octa-
?
2
?
3?
hedral sites. A ions and B ions are surrounded by four
and six oxygen ions, respectively. In the inverse spinel, the
cations distribution occurs by inverted (B)[AB]O4
arrangement, in which all the tetrahedral sites are occupied
Keywords Spinel Á Pigments Á Nickel Á Thermal behavior
?
3
2?
3?
by B cations, while an equal number of A and B
cations share the octahedral sites. The intermediate spinel
can be represented by (A1-xB )[A B2-x]O4 formula,
&
Renan M. Queiroz
renanmenezes@ufpa.br
x
x
where x is the degree of inversion and (A1-xB ) and
x
1
2
[A B2-x] represent the tetrahedral and octahedral sites,
x
Faculdade de Qu ´ı mica, ICEN, Universidade Federal do Par a´ ,
CP 479, Bel e´ m, PA 66075-110, Brazil
respectively [11, 12].
The chemical and physical properties of the metal oxi-
des depend on the synthetic route employed. Thus, several
methods like co-precipitation [13], hydrothermal synthesis
[8], solid-state reactions [14] and polymeric precursor [15]
have been reported in the literature to prepare metal oxides
with spinel structures. Compared to these chemical meth-
ods of synthesis, the polymeric precursor method, which is
Instituto de Qu ´ı mica, Universidade Federal do Rio de Janeiro,
Ilha do Fund a˜ o, CT bloco A, Rio de Janeiro, RJ 21941-909,
Brazil
3
4
Escola de Aplica c¸ a˜ o da UFPA, CP 479, Bel e´ m,
PA 66075-110, Brazil
Departamento de Qu ´ı mica, Universidade Federal da Para ´ı ba,
Jo a˜ o Pessoa, PB 58059-900, Brazil
123

R. M. Queiroz et al.
based on production of polyesters of metallic citrates, has
some advantages, such as high reproducibility, low crys-
tallization temperature, accurate stoichiometric control and
relatively low cost [16].
the system was heated at 70 °C. After 1 h, 58.75 mL of
ethylene glycol was slowly added. The heating was kept
until the volume was reduced to the half. With increasing
viscosity of the solution, the polymeric gel was formed.
The precursor powders were obtained by submitting the
resulting polymeric gels to a thermal treatment at 300 °C in
an oven, under air flow, for 2 h. Then, the precursor
powders were grounded and lastly calcined at 600, 800 and
1000 °C for 2 h in an oven. The other samples
(Ni Zn Al O , x = 0, 0.05, 0.10 and 1.0) were synthe-
Lisboa-Filho et al. [17] synthesized Ni Zn Sb O
2 12
x
7-x
spinel by the polymeric precursor method and studied the
2
?
2?
distribution of Zn
and Ni
ions in tetrahedral and
octahedral sites as a function of the amount of nickel
incorporated into the spinel. They concluded that up to
x = 3, nickel substitutes zinc in octahedral sites. For x [ 3,
x
1-x
2 4
2
?
Ni also occupies tetrahedral sites. Porta et al. [18] also
sized following the same procedure described for the
Ni0.15Zn0.85Al O sample, only adjusting the amounts of
2
studied the distribution of Ni in Ni Zn Al O spinel
?
x
1-x
2
4
2 4
obtained by a solid-state reaction process, with x ranging
metal sources to obtain the desired metal molar ratio in the
sample.
2
?
from 0.05 to 0.90. They have found that Ni preferentially
occupies octahedral sites and that it shifts a little toward a
random distribution (intermediate-type spinel) with
increasing temperature from 800 to 1200 °C. In the study
of Co Zn Sb O spinel (x = 0–7), synthesized by the
Instrumental analysis
X-ray diffraction (XRD), using powder method, was
x
7-x
2 12
polymeric precursor method, Gouveia et al. [19] stated that
the blue color of the pigment depends on the sites that the
chromophore ions occupy.
performed on a PANalytical X’PERT PRO MPD
(PW 3040/60) diffractometer, model PW 3710 BASED.
Radiation Cu K (0.15406 nm) was used. The 2h scanning
a
-
1
Considering that ZnAl O4 spinel may be used as a
2
speed was 0.02° s
Infrared spectra were recorded in the 800–400 cm
.
2
?
-1
chromophore ion support, and also that Ni is an ion that
can color ceramic materials, this manuscript reports on the
synthesis of ZnAl O spinel, by the polymeric precursor
spectral region by means of a Thermo IR100 spectrometer.
The surface area, diameter and pore volume were cal-
culated according to Brunauer–Emmett–Teller and Barret–
Joyner–Halenda (BET/BJH) method using a Quantachrome
NOVA 1200 equipment. Before the analysis, the samples
were heated at 250 °C for 2 h.
2
4
method. The influence of the temperature and the different
2
?
2?
degrees of substitution of Zn by Ni ion in the spinel
lattice were also investigated. The obtained oxides were
characterized by different structural and spectroscopic
techniques.
The thermal decomposition of the samples was inves-
tigated by thermogravimetric analysis (TG) and differential
thermal analysis (DTA). It used a Thermal Sciences ther-
mobalance (TG/DTA), model PL-STA. About 10 mg of
the samples was placed in platinum pans and heated from
room temperature to 1000 °C, at a heating rate of
Experimental
Materials
-
1
-1
1
0 °C min and using a synthetic air flow of 40 mL min
.
The chemicals were: nickel acetate (99 %, Vetec, Brazil),
zinc nitrate (97 %, Cromoline, Brazil), aluminum nitrate
98 %, Din aˆ mica, Brazil), citric acid (CA, 99 %, Vetec,
The UV–Vis absorption spectra were obtained in a
Shimadzu 2550 spectrophotometer. All data were collected
in the 300–800 nm region.
(
Brazil) and ethylene glycol (99 %, Vetec, Brazil). All of
the reactants were used as supplied.
The CIELab chromatic coordinates were taken by means
of a Gretac Macbeth Color-eye 2180 colorimeter, using a
D65 illumination.
Sample preparation
Ni Zn Al O oxides (x = 0, 0.05, 0.10, 0.15 and 1.0)
x
Results and discussion
1-x
2 4
were synthesized by a polymeric precursor method [10]. In
a typical procedure to synthesize 10 g of a sample with the
composition of Ni0.15Zn0.85Al O , 42.38 g of aluminum
Characterization by XRD
2
4
nitrate, 14.28 g of zinc nitrate and 2.09 g of nickel acetate
were slowly dissolved in 100 mL of distilled water. An
aqueous solution of citric acid, prepared using 98.12 g of
citric acid diluted in 100 mL of water, was added to this
system under vigorous stirring. The stirring was kept, and
The development of the spinel structure of ZnAl O and
2
4
NiAl O was confirmed by XRD technique (Fig. 1),
2
4
revealing that the synthesis route applied in this work (the
polymeric precursor method, at a relatively low temperate)
was efficient to produce the oxides. The XRD patterns
1
23

Structural and thermal characterization of Ni
x
Zn1-xAl
O
2 4
synthesized by the polymeric precursor…
(a)
(b)
ZnAl O
NiAl O
2
4
2
4
NiO
1000 °C
1000 °C
800 °C
8
00 °C
600 °C
600 °C
20
30
40
50
60
20
30
40
50
60
2θ/°
2θ/°
Fig. 1 XRD patterns of a ZnAl
2
O
4
and b NiAl
2
O
4
at 600, 800 and 1000 °C
show the characteristic peaks of ZnAl O and NiAl O
2 4
is also important to point out that there is a linear rela-
tionship between the crystallite size and synthesis
temperature.
2
4
spinels (JCPDS files 73–1962 and 10–0339 for ZnAl O4
2
and NiAl O , respectively). The XRD reflections suggested
2
4
that ZnAl O (Fig. 1a) is monophasic at all temperatures
2
4
and that NiAl O (Fig. 1b) presented a secondary phase
2
Characterization by infrared spectroscopy (IR)
4
related to NiO. As can be seen in Fig. 1b, as the calcination
temperature increased the intensity of the characteristics
peaks of this secondary phase decreased. These results
indicated that the recrystallization process might eliminate
oxygen and suggested that nickel was restructured into the
NiAl O spinel. The crystallinity of these systems
The IR spectra of the ZnAl O spinel at different calcina-
4
2
tion temperatures are given in Fig. 3. All samples pre-
-
sented absorption bands at about 505, 548 and 650 cm
1
that were ascribed to [AlO6] (octahedral) stretching
vibration [12]. The ZnAl O spinel showed an absorption
2
4
2 4
-
1
increased. This conclusion was reached given that well-
defined and more intense diffraction peaks were observed.
With increasing nickel doping (Ni Zn Al O , x = 0.05,
band at 430 cm
that can be attributed to the ZnO
stretching vibration [20]. The absence of the band at
-
around 730 cm , related to (AlO ; tetrahedral) stretching
1
x
1-x
2
4
4
0
.10 and 0.15), no differences in the XRD patterns were
vibration, showed that ZnAl O spinel is normal, with the
4
2
noticed. Average crystallite sizes of the samples are dis-
played in Fig. 2. It was found that crystallite size increases
in accordance with the nickel content in the sample, and it
divalent metal ion in tetrahedral sites, and the trivalent
metal ion in the octahedral sites [21].
-
1
The bands at around 430 and 410 cm became more
evident as the temperature increased. So, it was possible to
conclude that a better spinel structure can be obtained at
higher temperatures. Ni Zn Al O (x = 0.05; 0.10 and
1
1
1
6
4
2
Ni0.05Zn0.95Al O4
2
x
1-x
2 4
Ni0.10Zn0.90Al O4
2
Ni0.15Zn0.85Al O4
2
1
000 °C
00 °C
8
6
00 °C
600
700
800
900
1000
8
00
700
600
500
400
Temperature/°C
Wavenumber/cm–1
Fig. 2 Crystallite size of Ni
x 2 4
Zn1-xAl O (x = 0.05; 0.10 and 0.15),
heat-treated at 600, 800 and 1000 °C
2 4
Fig. 3 IR spectra of ZnAl O at different calcination temperatures
123

R. M. Queiroz et al.
0
.15) spinels calcined at 800 °C showed absorption band at
around 430 and 410 cm that can be attributed to the Ni-
are shown in Fig. 4a, b, respectively. All TG curves
exhibited three distinct mass loss regions. The first one
(about 8 %), between 42 and 180 °C, was associated with
desorption of water and gases physically adsorbed in the
structure of the materials. These results can be confirmed
by DTA curves that showed an endothermic peak in the
same temperature range. The second and the third ones
-
1
tetrahedral (NiO ) stretching vibration. These findings
4
were also observed by other researchers like Souza et al.
[
12], who considered that, in general, the spinel structures
display metal–oxygen absorption bands (M–O–M or O–M–
-
O) in the range of 500–900 cm
1
.
(about 48 %), in the range from 180 to 800 °C, and that
Characterization by N adsorption–desorption (BET
2
exhibited exothermic peaks, can be associated with the
consecutive thermal decomposition of the carbon chain
and BJH)
[
24]. Except NiAl O precursor powder sample, no mass
2 4
Surface area, pore diameter and pore volume were deter-
losses can be seen above 800 °C, indicating that pigments
are stable at high temperatures. The mass loss (about
4.53 %) observed above 800 °C for the NiAl O precursor
mined by N adsorption–desorption technique (see Table 1).
2
The obtained pore diameters were similar and indicated that
the oxides are mesoporous [22]. NiAl O spinel calcined at
2
4
powder was related to the elimination of oxygen due to the
2
4
2
-1
6
00 °C exhibited the largest surface area (156 m g ), and
structural rearrange of nickel in the NiAl O spinel, which
2
4
it can be observed that the surface area decreased as the
temperature increased. This result was expected since the
calcination promotes the sinterization of the crystallites,
which produces materials with lower surface areas [23].
is assigned by X-ray results.
Characterization by UV–Vis Spectroscopy
Figure 5 shows the absorption spectra in the UV–Vis
Thermal analysis (TG and DTA) characterization
region of samples Ni Zn Al O (x = 0.05, 0.10 and
x
1-x
2 4
0.15) heat-treated at 1000 °C. The absorption band at
The TG and DTA curves of the as-synthesized
approximately 632 nm can be related to the m4 transition
Td
3
3
3
Ni Zn Al O (x = 0, 0.05, 0.10, 0.15 and 1.0) samples
x
( T ? T ( P)), and the small band around 780 nm can
1-x
2
4
1
2
Table 1 BET and BJH results of the spinels
2
Surface area/m g
-1
3
Pore volume/cm g
-1
Sample
Pore diameter/nm
ZnAl
ZnAl
ZnAl
2
2
2
O
O
O
4
4
4
600 °C
800 °C
1000 °C
600 °C
800 °C
1000 °C
77
44
0.027
0.022
0.004
0.087
0.040
0.016
0.075
0.077
0.139
3.4
3.7
3.0
3.3
3.0
3.7
3.3
3.3
3.4
8
NiAl
NiAl
NiAl
2
O
O
O
4
156
71
2
2
4
4
37
Ni0.05Zn0.95Al
Ni0.10Zn0.90Al
Ni0.15Zn0.85Al
O
2 4
O
2 4
O
2 4
600 °C
600 °C
600 °C
83
78
122
Fig. 4 a TG and b DTA curves
of the Ni Zn1-xAl (x = 0,
.05, 0.10, 0.15 and 1.0)
samples
(
a)100
(b) 18
ZnAl O4
2
x
2 4
O
1
1
1
1
6
4
2
0
8
6
4
2
0
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Ni0.05Zn0.95Al O
0
2
4
4
4
Ni0.10Zn0.90Al O
2
Ni0.15Zn0.85Al O
2
NiAl O4
2
Exo
Endo
ZnAl O
2
4
Ni0.05Zn0.95Al O4
2
Ni0.10Zn0.90Al O4
2
Ni0.15Zn0.85Al O4
2
–2
–4
NiAl O
2
4
0
200
400
600
800
1000
0
200
400
600
800
1000
Temperature/°C
Temperature/°C
1
23

Structural and thermal characterization of Ni
x
Zn1-xAl
2
O
4
synthesized by the polymeric precursor…
Table 2 Colorimetric analysis of the Ni0.05Zn0.95Al O samples
0
0
0
0
0
0
.5
.4
.3
.2
.1
.0
2
4
Ni0.15Zn0.85Al O4
2
Ni0.10Zn0.90Al O4
Temperature/°C
00
800
000
L*
a*
b*
2
Ni0.05Zn0.95Al O4
2
6
71.35
77.00
77.39
-1.21
-5.27
-7.00
6.10
5.83
4.03
1
Table 3 Colorimetric analysis of the Ni
samples
x
Zn1-xAl
2
O
4
at 1000 °C
b*
3
00
400
500
600
700
800
x value in the Ni
x 2
Zn1-xAl O
4
formula
L*
a*
Wavelength/nm
0.05
0.10
0.15
1.0
72.01
77.39
69.52
56.44
-7.23
-7.00
-8.97
-8.40
9.11
4.03
Fig. 5 Absorption spectra in the UV–Vis region of the Ni
x
Zn1-x
Al O
2 4
(x = 0.05, 0.10 and 0.15) samples calcined at 1000 °C
1.56
-14.73
be assigned to the spin-forbidden m3Td transition
3
1
1
1
(
T ? T , E ( D)), which is generally observed in solid
1
2
materials [25]. According to the Tanabe–Sugano diagram,
Conclusions
besides the prohibited spin transitions observable in the
8
2?
near-UV–Vis region, a d ion like Ni in cubic coordi-
nation has three d–d allowed spin transitions, which may
occur in tetrahedral and octahedral electronic spectra [26].
According to Lorenzi et al. [10], the absorption bands
observed from 300 to 800 nm are the fingerprint of tetra-
The precursor polymeric method is efficient for obtaining
Ni Zn Al O pigments of spinel-type structure. The
x
1-x
2 4
obtained spinels were thermally stable, crystallized at rel-
atively low temperatures and had not significant interfering
phases. The results of the thermal analysis indicated that
these pigments are stable at high temperatures. UV–Vis
2?
hedral Ni , and that the blue color, which is characteristic
2
?
of this ion, was attributed to the occupation of Ni ions in
2?
results showed that Ni occupied tetrahedral sites. The
2
this kind of site. No signals related to Ni in octahedral
?
colorimetric coordinates showed that the intensity of the
2?
blue color of the pigments depends on the amount of Ni
2
?
sites were observed. These results indicated that the Ni
ion in the Ni Zn Al O pigments occupied tetrahedral
x
1-x
2 4
incorporated into the spinel-type structure. The calcination
temperature also influenced the color of the obtained
ceramic pigments, indicating that pigments (x = 0.05,
sites and that these pigments are blue.
0
.10, 0.15 and 1.0) are blue when they are calcined at high
Colorimetric analysis (CIELab)
temperatures.
The pigment colors were qualitatively and quantitatively
characterized by the CIELab method, where L*, a* and b*
parameters measure the brightness and the intensity of
red–green and yellow–blue colors, respectively. The
coordinates of Ni0.05Zn0.95Al O pigment, treated at dif-
Acknowledgements The authors would like to thank FINEP/
LAPAC and CNPq for the financial support.
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2
4
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values decreased as the calcination temperature increased.
In contrast, the values of L* increased as the calcination
temperature increased. With the obtained results, it was
possible to conclude that the lower the temperature,
the lighter the pigment. The chromatic coordinate
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