Valášková et al.
Structural Properties and Photocatalytic Activity of Ceria Nanoparticles on Vermiculite Matrix
In this contribution, the microstructures and photo-
catalytic activities of cerium oxides are compared that
were prepared from the (NH4ꢀ2Ce(NO3ꢀ6 precursor in
aqueous solution (sample CeO2) and in suspension with
vermiculite (sample Ver/CeO2). The microstructure was
analyzed by using X-ray powder diffraction (XRD) as
well as by using the high-resolution transmission electron
microscopy (HRTEM). The photocatalytic activity of the
samples was studied through the decomposition of N2O by
sole nanoparticles CeO2, CeO2 embedded in vermiculite,
and compared with the commercial Evonik P25 catalyst.
Japan). The XRD patterns of the samples pressed on
the glass slide were recorded in the symmetrical Bragg-
Brentano diffraction geometry in the 8–80ꢀ 2ꢄ range with
a scanning rate of 2ꢀ/min at 40 kV and 40 mA using a
scintillation counter as detector.
The surface area (SA) was measured with the Sorp-
tomatic 1990 instrument (Thermo Electron Corporation,
USA) by using nitrogen as adsorbing gas. The value of
SBET was calculated by employing the Advance Data Pro-
cessing software according to the BET isotherm. The size
distributions of the micro- and mesopores were calculated
by means of the Horvath-Kawazoe model.5
The morphology of the ceria nanoparticles and their
docking on the vermiculite matrix were visualized in
the high-resolution transmission electron microscope JEM
2200 FS from Jeol (Japan), which was equipped by a
corrector of the spherical aberration (Cs). The Cs cor-
rected HRTEM allows in particular the internal interfaces
and borders of small crystallites to be reproduced without
distortions.6
2. EXPERIMENTAL DETAILS
2.1. Starting Materials
Vermiculite from the Paraiba region of Brazil containing
a superfine particle size fraction (<2 mm), which was
purchased from Grena, Ltd. Czech Republic, was milled
and sieved to have the particle size <40 ꢁm. The chemi-
cal structural formula of a half unit cell was (Si3ꢂ12Al0ꢂ88
)
2+
(Al0ꢂ05Fe30+ꢂ37Fe0ꢂ03Mg2ꢂ50Ti0ꢂ05)O10(OH)2Ca0ꢂ10Na0ꢂ05K0ꢂ17
.
4
The decomposition of N2O on the surface of different
photocatalysts was investigated at ambient temperature in
a homemade apparatus. The respective photocatalyst was
spread on the adhesive tape, which was located at the bot-
tom of an annular batch reactor, and illuminated by an
8 W Hg lamp with the maximum intensity at 254 nm.
The reactor having the volume of 663 ml was filled with
Cerium nitrate hexahydrate (Ce(NO3ꢀ3 ·6H2O) from Sigma
Aldrich and ammonium hydroxide solution (NH4OH)
from Mach-chemicals, Czech Republic, were used as ceria
precursor.
2.2. Sample Preparation
Vermiculite (Ver) at aqueous dispersion 5 wt% was stirred
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968 ppm of the N O/He mixture (pressure of 110 kPa).
IP: 194.50.116.236 On: Fri, 08 Jul 2016 02:321:40
A gas chromatograph with a thermal conductivity detec-
tor GC/TCD was used for analysis of the N2O conversion
during the UV irradiation (Eq. (1)):
Copyright: American Scientific Publishers
for 15 min. The precursor of ceria was the solution of
80 ml of aqueous cerium nitrate Ce(NO3ꢀ3 ·6H2O (0.4 M)
and 13 ml of NH4OH (1.4 M) (pH = 11) stirred for
15 min at the room temperature (sample CeO2). The sam-
ple Ver/CeO2 was prepared from Ver in aqueous dispersion
(100 ml), which was added dropwise to the aqueous pre-
cursor of ceria, and further stirred for 3 h at 50 C. The
samples CeO2 and Ver/CeO2 were obtained by centrifu-
gation and washing several times with distilled water and
hvꢅcatalyst
N2O −−−−−→ N2 +1/2O2
(1)
ꢀ
The relative amount of converted N2O was determined
according to Eq. (2), assuming that the total pressure in
the reactor can be considered as constant due to a low N2O
ꢀ
concentration.
then dried overnight in an oven at 80 C.
cN0 O −cN O
2
2
XN O
=
(2)
0
2
c
N2O
2.3. Characterization Methods
In Eq. (2), cN0 O and cN O are the N2O concentrations prior
The elemental analysis of vermiculite was performed by
using the energy dispersive X-ray fluorescence (XRF)
spectrometer SpectroXepos (Spectro Analytical Instru-
ments, Germany) and the atomic emission spectrome-
ter with inductively coupled plasma (ICP-AES) Spectro
Vision (Spectro Analytical Instruments, Germany). The
elements in the water solution were quantified using
the ICP-AES JY 24 from Spectro Analytical Instrument
(Germany).
The changes in the basal lattice plane spacing of vermi-
culite after the reaction with Ce(NO3ꢀ3 ·6H2O and NH4OH
were determined by using XRD analysis. The analysis of
the XRD line broadening revealed the size of CeO2 crys-
tallites. The XRD analysis was performed with CuKꢃ radi-
ation on the X-ray diffractometer Ultima IV (RIGAKU,
2
2
to the photocatalytic reaction (t = 0) and in the course of
the reaction, respectively.
3. RESULTS AND DISCUSSION
3.1. Formation of the Ver/CeO2 Composite
The reaction conditions facilitated the hydrolysis of
(NH4ꢀ2Ce(NO3ꢀ6 and the formation of the [Ce6(OH)12]12+
polyoxocations and the ceriumꢆIVꢀ hydroxide Ce(OH)4.2
The reaction of the polyoxocations with Ver was assumed
to follow the scheme (3):
ꢇꢈCe6ꢆOHꢀ12ꢉ12+ꢊ+Ver →→ ꢈCexꢆOHꢀyꢉ·Ver +zI+
→→ Ver/CeO2
(3)
J. Nanosci. Nanotechnol. 16, 7844–7848, 2016
7845