Synthesis of CaCu3Ti4O12, Study of Physicochemical and Photocatalytic Properties

Article abstract of DOI:10.1134/S0036023620100095

Abstract: Precursor CaCu₃Ti₄O₁₂ has been obtained using solution method in acetic acid medium, it was annealed at 100, 200, 400, 600 800, and 1100°C. Sintered powders have been studied by physicochemical methods of analysi

Full text of DOI:10.1134/S0036023620100095

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2020, Vol. 65, No. 10, pp. 1541–1546. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Neorganicheskoi Khimii, 2020, Vol. 65, No. 10, pp. 1338–1344.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis of CaCu3Ti4O12, Study
of Physicochemical and Photocatalytic Properties
K. V. Ivanova, *, O. V. Alekseevaa, and A. V. Agafonova
aKrestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, 153045 Russia
*e-mail: ivk@isc-ras.ru
Received May 7, 2020; revised May 25, 2020; accepted May 27, 2020
Abstract―Precursor CaCu3Ti4O12 has been obtained using solution method in acetic acid medium, it was
annealed at 100, 200, 400, 600 800, and 1100°C. Sintered powders have been studied by physicochemical
methods of analysis. According to X-ray powder diffraction, completely formed crystal structure CaCu3Ti4O12
exists at 1100°C, the particle size of the prepared powder is 1–10 μm. Thermal analysis with allowance for
mass spectrometric analysis system of vapor phase has revealed process mechanisms. Effect of dried at 100°C
powder of precursor and CaCu3Ti4O12 on the photocatalytic activity of Rhodamine B decoloration has been
shown. Pseudo-first and pseudo-second order kinetics for Rhodamine B adsorption on samples annealed at
100 and 1100°C has been revealed.
Keywords: thermal treatment, synthesis, kinetics, photocatalytic activity
DOI: 10.1134/S0036023620100095
INTRODUCTION
in visible light resulting from charge transfer in visible
light from the main to the excited state.
In recent time, a large attention is attracted to the
studies of photocatalytic activity of materials with per-
ovskite structure to design photocatalysts [1, 2] useful
in decontamination systems of aqueous and air media
from organic molecules (dyes, pharmaceuticals) and
bacteria [3–5]. The development of photocatalysts
active on exposure to visible light is of special interest.
However, widely known titanium dioxide used as pho-
toactive material has drawbacks due to its low photo-
sensitivity in visible spectral region because of large
band gap width. One of the methods to extend TiO2
absorption region to visible spectrum is the doping of
titanium dioxide with transition metals or other com-
pounds. A number of works were devoted to study
metal oxides [6], hybrid [7], hetero structurized [8],
and other systems.
Literature provides the data on the investigation of
materials with perovskite structure such as BaTiO3 [9],
SrTiO3 [10], CaTiO3 [11], LaFeO3 [12], etc., showing
good photocatalytic activity. However, they have wide
band gaps (>3 eV) and can be activated only in ultraviolet
light [13]. The authors [14] found that CaCu3Ti4O12
(CCTO) has two band gaps: 1.93 and 2.21 eV. There-
fore the study of photocatalytic properties of CCTO,
which is double cubic perovskite [15] prepared by dif-
ferent methods, seems to be topical because it com-
bines the photocatalytic properties of TiO2 [16] show-
ing high activity in ultraviolet and CuO that absorbs
visible light. The combination of properties of these
oxides in CCTO should favor to photocatalytic activity
Titanium dioxide is known to show antimicrobial
and antimycotic properties preferably on exposure to
light [17]. The doping of TiO2 with metal ions or
designing nanosized composites using different oxides
(CuO, Ag2O, etc.) leads to emergence of antimicrobial
activity in the dark [18–20]. The use of such materials
as CaCu3Ti4O12 allows one to design coatings on textile
materials for medicinal purposes and aids for respira-
tory tract protection.
It should be noted that literature includes mainly
reports on the studies of dielectric permittivity of
CCTO due to its possible application in microelec-
tronics [21, 22].
The aim of this work is to synthesize and study the
structure and photocatalytic activity of CCTO.
EXPERIMENTAL
The precursor of ceramic powder of CCTO was
synthesized by liquid-phase method in acetic acid
medium. Initial reagents used were Ca(OH)2,
Cu(CH3COO)2 · H2O, Ti(C4H9O)4 (in stoichiometric
ratio CaO : CuO : TiO2 = 1 : 3 : 4), and glacial acetic
acid (all chemicals from SIGMA-Aldrich). Synthesis
procedure consisted in the preparation of aqueous
solution of Cu(CH3COO)2 · H2O and a solution of cal-
cium acetate by the reaction of Ca(OH)2 with
CH3COOH (glacial). The obtained solutions were
1541

1542
IVANOV et al.
5 μm
5 μm
(а)
(b)
Fig. 1. SEM images of powder at (a) 100 and (b) 1100°C.
I
mal analysis of the prepared powder was carried out on
a Netzsch STA 409 C/CD instrument. X-ray diffrac-
tion study of the prepared powders was performed on
a DRON-3M diffractometer (CuKα radiation, voltage
40 kV). IR spectra of powders of the prepared com-
pounds as KBr pellets were recorded on a Vertex 80v
Fourier transform IR spectrometer. The photocata-
lytic activity of the powder was studied by spectropho-
tometry on exposure of rhodamine solution in a sus-
pension of 0.043 g of photocatalyst powder in a 1-L
quartz thermostated cell to ultraviolet light. A 250-W
high-pressure mercury lamp with radiation maxi-
mum at 365 nm was used as a source of ultraviolet
radiation. The installation was described in detail in
the work [23].
CaCu3Ti4O12 CaTiO3 TiO2
CaO CaCO3
100°С
200°С
400°С
600°С
800°С
1100°С
RESULTS AND DISCUSSION
Physicochemical Characteristics of Prepared Materials
Figures 1a and 1b show electronic micrographs of
surfaces of the obtained powders and annealed for 1 h
at 100 and 1100°C. The micrographs show that the
materials have polydisperse structure. Thermally
treated sample at 100°C and applied voltage 5.0 kV
during measurement is a combination of agglomerates
as a disordered and lamellar structure. The size of
these grains is 500 nm–8 μm. The sintering at 1100°C
and applied voltage of 15.0 kV during recording leads
to emergence of larger aggregates having a rounded
cubic shape and size from 1 to 10 μm, which is caused
by sintering processes and crystalline structure forma-
tion. The surface of the obtained material is a large
structure with small number of pores.
10
20
30
40
50
60
70
80
2θ, deg
Fig. 2. XRD of prepared thermally treated powder.
mixed and stirred for 1 h at 85°C. Titanium butoxide
was added dropwise to the homogeneous solution and
kept for 1 h at continuous heating (85°C) and stirring.
The solution was dried in a drying cabinet at 100°C
until constant weight and annealed in air at tempera-
tures 200, 400, 600, 800, and 1100°C.
The X-ray powder diffraction study of change in
The samples of thermally treated powders were the crystal structure of the prepared powder during
studied by physicochemical methods of analysis. Pow- thermal treatment (Fig. 2) allowed us to reveal the
der morphology was studied by scanning electron process of CCTO phase formation in the range from
microscopy (a Vega3 SBH Tescan microscope). Ther- 100 and 1100°C.
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SYNTHESIS OF CaCu3Ti4O12, STUDY OF PHYSICOCHEMICAL
DTG, %/min
1543
TG, %
DSC, mW/mg
2.0
100
90
80
70
60
50
40
30
20
10
DTG
0
exo
1.5
1.0
0.5
0
–2
–4
–6
–8
–10
DSC
0
200
400
600
800
1000
T, °C
Fig. 3. Thermogram of the prepared powder.
The nucleation of CaCu3Ti4O12 crystallites is
observed at 400°C, which is evidenced by the presence
of reflections 2θ = 29.57°, 38.47°, 49.38°, and 61.45°.
Further increase in treatment temperature is accom-
panied by the emergence of new reflections on diffrac-
togram and the growth of crystalline phase of CCTO
whose formation completed at 1100°C (2θ = 29.57°,
34.45°, 38.47°, 42.36°, 49.38°, 52.53° 61.45°, 72.32°,
74.92°). As Fig. 2 shows, the powders contain admix-
The portion of gravimetric curve from 320 to 600°C
(the second stage) displays weight loss (7.4%) due to
decomposition of complexes of titanium isobutoxide
with acetic acid to titanium dioxide and products of
organic compound destruction. The subsequent
change of sample weight at 600–1000°C (the third
stage) corresponds to the decomposition of calcium
carbonate present in material as intermediate product
and formation of CaCu3Ti4O12. The total weight loss of
tures of calcium carbonate (2θ = 47.53°, 48.52°), tita- sample is 48.5%.
nium dioxide as rutile phase (2θ = 27.46°, 34.88°,
36.12°, 41,28°, 44,08°, 54.37°, 56.68°, 68.82°, 69.07°),
calcium oxide (2θ = 64.71°, 67.97°), and calcium tita-
nate (2θ = 33.4°, 59.68°). Their considerable amount
was found for powder annealed at 800°C. The size of
crystallites calculated by the Scherrer equation (D =
0.94λ/(B cosθ)), at 800°C equals to 31 nm, that at
1100°C is 35 nm.
Thermal analysis of the prepared powder (Fig. 3)
performed in combination with mass spectra identifi-
cation for gas phase by ion current (Fig. 4) enables us
to consider in detail thermal processes in the material
on thermal destruction. Thermogram shows three
stages. The first stage is sample heating to ∼320°C,
resulting in weight loss 36.5% due to removal of water,
acetate groups, and acetone according to the data of
mass spectra of ion currents. The formation of acetone
detected in Fig. 4 seems to be caused by the decompo-
sition of acetic acid excess on heating:
The IR spectra of prepared powder (Fig. 5) in tem-
perature range 100–800°C shows absorption bands of
adsorbed water in the range 3670–3250 cm–1.
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
H2O
CO
CH3COOH
C3H6O
C
CO2
O2
0
200
400
600
800
1000
T, °C
CH3COOH → (CH3)2CO + CO2 +H2O,
as well as acetates in the prepared powder.
Fig. 4. Ion currents for the prepared powder.
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1544
IVANOV et al.
Photocatalytic Measurements
I
O–H
C–O–Ti
100°С
The photocatalytic activity of the powder, CCTO
precursor dried at 100°C and CaCu3Ti4O12 powder
obtained by thermal annealing at 1100°C was studied
using the reaction of photocatalytic decoloration of
Rhodamine B dye as an example.
200°C
400°C
600°C
Figure 6 shows change in the absorption spectra of
aqueous solution of Rhodamine B on exposure to
ultraviolet radiation from a 250-W high-pressure lamp
with maximum at 365 nm. Absorption maximum for
Rhodamine B is 552 nm. Figure 6 shows that maxi-
mum intensity decreases when irradiation time
increases, solution color changes from bright violet to
colorless. Adsorption spectra exhibit a shift of absorp-
tion maximum (especially in Fig. 6a) probably due to
effect of the powder containing organic groups, in par-
ticular acetate, which affect the wavelength shift
during irradiation of aqueous suspension and owing to
solution decoloration (Fig. 6b).
C–O
Ca–Cu–Ti–O
800°C
1100°С
4500 4000 3500 3000 2500 2000 1500 1000 500
0
ν, cm–1
Fig. 5. IR spectra of the annealed powder.
The results of efficiency of photocatalytic decom-
position of Rhodamine B in Fig. 7 display that the
most complete degradation of the dye in aqueous solu-
The heating of the powder from 100 to 200°C leads
to emergence of bands at 1580 and 1430 cm–1 corre-
sponding to bidentate acetate bridging group. It tion occurs when CCTO powder obtained by the ther-
degrades on further heating. The formation of carbon- mal treatment of precursor at 1100°C is used as a pho-
ate groups corresponding to C–O vibrations at 1456
and 860 cm–1 seems to proceed on further heating,
which is confirmed by X-ray powder diffraction and
thermogravimetric analysis with allowance for evolved
gases.
The IR spectrum of powder annealed at 800 and
1100°C displays bands at 561, 516, and 441 cm–1 indi-
cating the presence of CCTO. The authors [24] believe
that these vibrations are related to titanium ions (Ti–
O 653–550 cm–1 and Ti–O–Ti 495–436 cm–1).
tocatalyst. In this case, dye decoloration was 84.4%,
whereas the use of the powder annealed at 100°C led
to decoloration of 52.1%. The difference in the values
of photocatalytic activity of the powders seems to be
due to the difference in the phase composition, crys-
tallinity degree, and the presence of active centers.
To analyze the process of dye adsorption, we used a
general kinetic model of chemical reactions, namely
the Lagergren model of pseudo-first and pseudo-sec-
ond order kinetics. The pseudo-first-order rate model
I
I
30
0 min
2 min
5 min
0 min
(b)
0.12
0.10
0.08
0.06
0.04
0.02
0
(a)
2 min
25
5 min
10 min
15 min
20 min
30 min
40 min
50 min
60 min
90 min
10 min
15 min
20 min
30 min
40 min
50 min
60 min
90 min
20
15
10
5
0
450
500
λ, nm
550
600
450
500
λ, nm
550
600
Fig. 6. Absorption spectra of Rhodamine B on exposure to ultraviolet in aqueous solution by the powder annealed at (a) 100, (b)
1100°C.
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SYNTHESIS OF CaCu3Ti4O12, STUDY OF PHYSICOCHEMICAL
1545
In the dark
Ultraviolet
0
–0.5
–1.0
–1.5
–2.0
1.0
0.8
0.6
0.4
0.2
100°С
R2 = 0.65416
100°С
1100°C
1100°C
R2 = 0.94459
40 60
0
0
10 20 30 40 50 60 70 80 90 100
t, min
0
20
80
100
t, min
Fig. 7. Photocatalytic decomposition of Rhodamine B on
catalyst powders annealed at 100 and 1100°C in the dark
and on exposure to ultraviolet.
Fig. 8. Pseudo-first-order model kinetics for Rhodamine
B adsorption on samples annealed at 100 and 1100°C.
suggested by Lagergren [25] is expressed by the equa-
tion:
6
ln(qe – qt) = ln qe – k1t,
5
R2 = 0.93415
where qe and qt (mg/g) is the amount of adsorbed
Rhodamine B in equilibrium state and at the definite
time point, respectively; t is the time of contact (min);
k1 is pseudo-first-order rate constant (min–1) deter-
mined from the slope of section ln(qe – qt) to t.
The linearized pseudo-second-order model is
expressed by the following equation [26]:
4
3
2
1
R2 = 0.99837
t
qt
1
t
qe
=
+
,
k2qe2
0
were k2 is the pseudo-second-order rate constant,
g/(mg min).
0
20
40
60
80
100
t, min
According to the plot shown in Fig. 8 for the model
of pseudo-first-order kinetics, the values of R2 (cor-
relation coefficient) of Rhodamine B adsorption on
samples are within 0.65 to 0.94. Experimentally
observed kinetics for adsorption on powder dried at
100°C is insufficiently described by the pseudo-first-
order model because of linear dependences only at
short time of phase contact. The obtained shape of
dependence in the noted coordinates probably indi-
cates the mixed diffusion kinetics of sorption process
and provides no possibility to unambiguously reveal
limiting stage. Rate constants for pseudo-first-order
kinetic model were 0.00814 min–1 for powder CCTO
precursor dried at 100°C and 0.02261 min–1 for
CaCu3Ti4O12.
Fig. 9. Pseudo-second-order model kinetics for
Rhodamine B adsorption on samples annealed at 100 and
1100°C.
order model describes the kinetics for CCTO obtained
by thermal treatment at 1100°C rather well. The
pseudo-second-order model agree well with the sam-
ple dried at 100°C, which indicates that adsorption
includes both chemical and physical sorption [26].
CONCLUSIONS
Compound CaCu3Ti4O12 was obtained by the ther-
mal treatment at 1100°C of precursor prepared by
solution method. Scanning electron microscopy
The pseudo-second-order kinetics of Rhodamine
B adsorption model (Fig. 9) provides the R2 value of showed that the size of particles of the synthesized
0.99837 for the sample annealed at 100°C and 0.93415 powder dried at 100°C is 1–2 μm, while that of CCTO
for the sample annealed at 1100°C, the rate constant is is 2–5 μm. The processes occurred on the thermal
0.02 and 0.06, respectively. In summary, pseudo-first- treatment of the prepared matter were studied by a
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 65 No. 10 2020

1546
IVANOV et al.
9. J. Li, G. Zhang, S. Han, et al., Chem. Commun. 54,
723 (2018).
number of physicochemical methods of analysis. It
was revealed that the formation of CaCu3Ti4O12 phase
completes at 1100°C. Adsorption kinetics for powder
with CaCu3Ti4O12 crystalline phase corresponds to
pseudo-first-order model, while that for precursor
agrees with pseudo-second-order model. It was found
that, over the first 15 min, more than 30% of
Rhodamine B is removed under the action the
obtained samples in the dark. The highest photocata-
lytic activity is shown by the powder with CCTO crys-
talline phase where Rhodamine B removal is ∼84.4%.
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ACKNOWLEDGMENTS
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The authors thank to the Shared Facility Center, Upper
Volga Regional Center for Physicochemical Studies.
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FUNDING
(2016).
This work was supported by the Ministry of Science and
Higher Education of the Russian Federation (State assign-
ment no. 01201260483) and partially supported by the Rus-
sian Foundation for Basic Research (project no. 18-43-
370015).
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CONFLICT OF INTEREST
https://doi.org/10.1016/j.vacuum.2020.109346
The authors declare no conflict of interest.
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Translated by I. Kudryavtsev
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