Synthesis and Characterization of CeO2 Nanoparticles via Solution Combustion Method for Photocatalytic and Antibacterial Activity Studies

Article abstract of DOI:10.1002/open.201402046

CeO₂ nanoparticles have been proven to be competent photocatalysts for environmental applications because of their strong redox ability, nontoxicity, long-term stability, and low cost. We have synthesized CeO₂ nanoparticles via solution combustion method using ceric ammonium nitrate as an oxidizer and ethylenediaminetetraacetic acid (EDTA) as fuel at 450°C. These nanoparticles exhibit good photocatalytic degradation and antibacterial activity. The obtained product was characterized by various techniques. X-ray diffraction data confirms a cerianite structure: a cubic phase CeO₂ having crystallite size of 35 nm. The infrared spectrum shows a strong band below 700 cm^-1 due to the Ce-O-Ce stretching vibrations. The UV/Vis spectrum shows maximum absorption at 302 nm. The photoluminescence spectrum shows characteristic peaks of CeO₂ nanoparticles. Scanning electron microscopy (SEM) images clearly show the presence of a porous network with a lot of voids. From transmission electron microscopy (TEM) images, it is clear that the particles are almost spherical, and the average size of the nanoparticles is found to be 42 nm. CeO₂ nanoparticles exhibit photocatalytic activity against trypan blue at pH 10 in UV light, and the reaction follows pseudo first-order kinetics. Finally, CeO₂ nanoparticles also reduce Cr^VI to Cr^III and show antibacterial activity against Pseudomonas aeruginosa.

Full text of DOI:10.1002/open.201402046

DOI: 10.1002/open.201402046
Synthesis and Characterization of CeO2 Nanoparticles via
Solution Combustion Method for Photocatalytic and
Antibacterial Activity Studies
Thammadihalli Nanjundaiah Ravishankar,[a] Thippeswamy Ramakrishnappa,*[a]
Ganganagappa Nagaraju,*[b] and Hanumanaika Rajanaika[c]
CeO2 nanoparticles have been proven to be competent photo-
catalysts for environmental applications because of their
strong redox ability, nontoxicity, long-term stability, and low
cost. We have synthesized CeO2 nanoparticles via solution
combustion method using ceric ammonium nitrate as an oxi-
dizer and ethylenediaminetetraacetic acid (EDTA) as fuel at
4508C. These nanoparticles exhibit good photocatalytic degra-
dation and antibacterial activity. The obtained product was
characterized by various techniques. X-ray diffraction data con-
firms a cerianite structure: a cubic phase CeO2 having crystal-
lite size of 35 nm. The infrared spectrum shows a strong band
below 700 cmꢀ1 due to the CeꢀOꢀCe stretching vibrations.
The UV/Vis spectrum shows maximum absorption at 302 nm.
The photoluminescence spectrum shows characteristic peaks
of CeO2 nanoparticles. Scanning electron microscopy (SEM)
images clearly show the presence of a porous network with
a lot of voids. From transmission electron microscopy (TEM)
images, it is clear that the particles are almost spherical, and
the average size of the nanoparticles is found to be 42 nm.
CeO2 nanoparticles exhibit photocatalytic activity against
trypan blue at pH 10 in UV light, and the reaction follows
pseudo first-order kinetics. Finally, CeO2 nanoparticles also
reduce CrVI to CrIII and show antibacterial activity against Pseu-
domonas aeruginosa.
1. Introduction
CeO2 nanoparticles are interesting due to their wide variety of
applications in polishing agents, sunscreens, solid electrolytes,
solar cells, fuel cells, phosphorescent/luminescent materials,
photocatalysis, sensors, oxygen pumps, and metallurgy.[1]
These applications take advantage of cerium’s high thermody-
namic affinity for oxygen and sulfur, its potential redox chemis-
try involving CeIII/CeIV and the unique and useful absorption/
excitation energy bands associated with its electronic struc-
ture.[2] Cerium is a lanthanide series rare earth element and
exists as a free metal or oscillates between the CeIII and CeIV ox-
idation states. Nanoceria (cerium oxide nanoparticles) also hop
between CeIII and CeIV valence states and they contain oxygen
vacancies that allow the nanoparticles to act as regenerative
catalysts.[3]
Dyes from textile, paper, and other industries are prime ex-
amples of environmental contaminants. Nowadays, the pres-
ence of pollutant organic dyes in wastewater has become a se-
rious problem.[4,5] Among these dyes, trypan blue is one of the
most widely used dye in these industries. Trypan blue, an azo
dye reported as a carcinogen,[6] creates several environmental
problems by releasing highly toxic molecules into bodies of
water. It has a highly stable complex structure. Thus, there is
a need for an efficient and economical method for the degra-
dation of such highly photostable compounds.[7,8,9] Various
techniques available for the complete removal of toxic dyes
present in wastewater can be subdivided into four main
groups: 1) physical techniques, 2) chemical/photocatalytic deg-
radation of dyes, 3) electrochemical techniques, and 4) biologi-
cal processes.[10] Among these methods, photocatalytic degra-
dation of dyes using UV light is one of the most prominent
techniques because the reactions are carried out under ambi-
ent conditions that are cost-effective and simple.[11,12] Various
photocatalysts like TiO2, ZnO, WO3, CeO2, and ZrO2 nanoparti-
cles are used for degradation of organic dyes.[13,14] Out of these
catalysts, CeO2 nanoparticles have been proven to be compe-
tent photocatalysts for environmental applications because of
their strong redox ability, nontoxicity, long-term stability, and
low cost.[15] Various methods available to prepare CeO2 nano-
particles include hydrothermal, solvothermal, coprecipitation,
sol-gel, solution combustion, and sonochemical methods.[16,17]
Solution combustion synthesis has an edge over other meth-
ods as it is considered simple, instantaneous, single-step, and
energy saving.[18] Here we report the synthesis of CeO2 nano-
[a] T. N. Ravishankar, T. Ramakrishnappa
Centre for Nano and Material Sciences, Jain University
Jakkasandra, Kanakapura (India)
E-mail: t.ramakrishnappa@jainuniversity.ac.in
[b] G. Nagaraju
Department of Chemistry, Siddaganga Institute of Technology
Tumkur, Karnataka (India)
E-mail: nagarajugn@rediffmail.com
[c] H. Rajanaika
Department of Studies and Research in Environmental Science
Tumkur University, Tumkur, Karnataka (India)
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This is an open access article under the terms of the Creative Commons
Attribution-NonCommercial License, which permits use, distribution and
reproduction in any medium, provided the original work is properly
cited and is not used for commercial purposes.
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particles using ceric ammonium nitrate as an oxidizer and eth-
ylenediaminetetraacetic acid (EDTA) as a fuel for the first time.
EDTA is used as fuel because it is nontoxic, cheap, and rich in
carbon, nitrogen, hydrogen, and oxygen which are released as
their corresponding oxides during combustion. The release of
these gases leads to the formation of highly porous CeO2
nanoparticles with a greater surface area. This paper focuses
on the applications of these CeO2 nanoparticles in the photo-
degradation of trypan blue, antimicrobial activity, and reduc-
tion of CrVI to CrIII.
The crystallite size calculated from the most intense peaks
(2q=28.58) by the Scherrer formula was found to be 35 nm.
2.2 Fourier transform infrared (FTIR) and UV/Vis spectroscopy
The FTIR spectrum (Figure 1b) shows a band at ~3480 cmꢀ1
which can be indexed to water molecules. The bands from
1200–2000 cmꢀ1 are due to organic moieties. The spectrum ex-
hibits strong bands below 700 cmꢀ1 due to the CeꢀOꢀCe
stretching vibrations.
The UV/Vis spectrum of CeO2 nanoparticles (Figure 1c)
shows a maximum absorption at 302 nm corresponding to the
band gap of 4.1 eV, which was blue shifted compared to that
of bulk material. The optical properties are strongly dependent
on the particle size. The origin of blue shift may be due to size
effects.[19]
2. Results and Discussion
2.1 X-ray diffraction
Figure 1a shows the X-ray diffraction (XRD) pattern of CeO2
nanoparticles synthesized by solution combustion method.
XRD was used to check the purity and crystallinity of the nano-
crystals. All the diffraction peaks of CeO2 are indexed to cerian-
ite-(Ce): syn structure with cubic phase, lattice points a=b=
c=5.41134 ꢁ, space group: Fm-3m (no. 225) and Joint Com-
mittee on Powder Diffraction Standards (JCPDS) no. 34-394.
2.3 Photoluminescence (PL) study
Figure 1d shows the PL spectrum of CeO2 nanoparticles with
an excitation wavelength of 350 nm. It mainly consists of five
emission bands: a strong blue emission band at 426 nm
(2.9 eV), a strong blue band at 441 nm (2.8 eV), a blue band at
Figure 1. Characterization of CeO2 nanoparticles prepared via solution combustion method. a) Powder XRD pattern; b) FTIR spectrum; c) UV/Vis spectrum;
d) Phospholuminescence (PL) spectrum.
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Figure 2. Microscopy images of CeO2 nanoparticles prepared via solution combustion method. a) SEM image (Scale bar: 20 mm); b) SEM image (Scale bar:
10 mm.); c) TEM image.
466 nm (2.7 eV), a strong blue-green band at 481 nm (2.6 eV),
and a green band at 532 nm (2.33 eV). Our results are consis-
tent with that reported for CeO2 in literature.[20] Strong emis-
sion peaks at 414 nm and 422 nm are observed for CeO2 nano-
particles. Maensiri et al.[21] reported a blue band at approxi-
mately 443 nm, along with a green band at 529 nm. The blue
shift of the PL peak depends on the size of CeO2 nanoparticles.
This phenomenon has been explained by charge transitions
from the 4f band to the valence band of the CeO2 nanoparti-
cles.[22] In addition, it is well known that the band gap energy
between the 4f band, and the valence band of CeO2 nanopar-
ticles varies from 3.0 to 3.38 eV. It depends on the particle size
of CeO2 nanoparticles and it can be determined from the cal-
culation of the electronic structure of CeO2.[23] Therefore, the
emission in our CeO2 samples could be due to the transition
from the Ce 4f band to the O 2p band (valence band) in CeO2.
The broad PL band ranging from 410 to 540 nm could be the
result of defects, including oxygen vacancies in the crystal with
electronic energy levels below the 4f band.[24] This is confirmed
by the enhanced absorption tail below 3 eV in nonstoichiomet-
ric CeO2 that was previously observed and attributed to the
presence of oxygen vacancies.[25]
Figure 3. N2 gas adsorption–desorption isotherm of CeO2 nanoparticles.
Figure insert: pore diameter of CeO2 nanoparticles prepared via solution
combustion method.
2.4 Scanning electron microscopy (SEM) and transmission
electron microscopy (TEM)
IV pattern with the presence of a hysteresis loop. The Bruna-
Figures 2a–b show the SEM images of CeO2 nanoparticles syn-
thesized by the solution combustion method. This type of
porous network with lot of voids is typical of combustion-syn-
thesized powders due to escaping gases. The TEM image (Fig-
ure 2c) shows that the particles are almost spherical in shape,
and the average nanoparticle size is found to be 42 nm. This
result resembles the crystallite size calculated using Scherer’s
formula.
uer–Emmett–Teller (BET) surface area analysis was found to be
163.5 m2 gꢀ1 which is higher than the reported values. Ching
and co-workers synthesized CeO2 nanoparticles through the
self-assembly of functionalized nanoparticles in a liquid-crystal
phase and reported a surface area of 125 m2 gꢀ1 [26]
Pan and
.
co-workers explained that the BET surface area greatly influen-
ces the catalytic activity. They have also reported the BET sur-
face area of CeO2 nanorods, nanoparticles, and nanotubes as
52.5, 37.2, and 80.1 m2 gꢀ1 respectively.[27] Fang and co-workers
reported the BET surface area of bulk CeO2 (5.67 m2 gꢀ1), CeO2
2.5 Surface area and pore diameter
nanoparticles
(30.33 m2 gꢀ1),
and
CeO2
nanotubes
Figure 3 shows the N2 adsorption–desorption isotherms along
with the Barret–Joyner—Halenda (BJH) pore size distribution
plot of CeO2 nanoparticles, and it exhibits a typical IUPAC type
(83.15 m2 gꢀ1).[28] Based on the BJH equation, the main pore
size of our CeO2 nanoparticles is 2.9 nm, as given in the inset
of Figure 3.
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Figure 4. Effect of a) dye concentration, b) catalytic load, c) pH, and d) light source on the photocatalytic activity of CeO2 nanoparticles.
2.6 Photocatalytic Activity of CeO2 nanoparticles in UV light
2.6.2 Effect of catalyst load
The effect of catalyst load on the photocatalytic degradation
of the dye is as shown in Figure 4b. In order to determine the
optimal dosage of the catalyst; the catalytic load was varied
from 0.1 to 0.5 g/100 mL. The optimal load was found to be
0.4 g/100 mL. Above the optimal load, the turbidity of the
slurry increases, light penetration decreases, and thus the avail-
ability of hydroxides and superoxides becomes minimal;
hence, photocatalytic activity also decreases.
2.6.1 Effect of dye concentration
Figure 4a shows the effect of dye concentration on the photo-
catalytic activity of CeO2 nanoparticles. The experimental con-
centration range of trypan blue was 5–25 mgLꢀ1. Catalytic load
was maintained at 0.4 g and pH 10. As the dye concentration
increases, the time taken for complete degradation of the dye
also increases. When the dye concentration is smaller, many
active sites in the photocatalyst lie vacant; hence the slurry re-
mains almost clear, enabling light penetration. Light penetra-
tion helps in photodegradation. With an increase in the dye
concentration, the active sites get occupied by the dye mole-
cules, and this trend continues until all the sites are fully filled
which occurs at a specified optimum concentration. Beyond
this concentration, the slurry gets turbid, preventing light pen-
etration resulting in decreased degradation.
2.6.3 Effect of pH
Figure 4c shows the effect of pH on the photocatalytic degra-
dation of trypan blue. From the figure, it is clear that the pho-
tocatalytic process strongly depends on the pH of the dye so-
lution.[29] The pH of the solution is adjusted by the addition of
either 0.1m NaOH or 0.1m H2SO4. The degradation efficiency is
higher in basic than in acidic conditions. This observation
agrees well with the reported studies.[30] The variation of pH
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alters the surface properties of CeO2, and, in turn, the dissocia-
C
tion of the dye molecules. At pH 10, perhydroxyl radicals (HO2 )
are formed, leading to the formation of hydrogen peroxide
[30]
C
which gives rise to a number of hydroxyl radicals (HO ). The
highest photocatalytic degradation observed in the case of
CeO2 is at pH 10.
The mechanism of formation of possible radicals is as given
below:
ꢀ
Cꢀ
O2 þ ecb ! O2
Cꢀ
ð1Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ð6Þ
ð7Þ
ð8Þ
ð9Þ
ð10Þ
O2 þ Hþ ! HO2
C
C
C
HO2 þ HO2 ! H2O2 þ O2
ꢀ
ꢀ
C
H2O2 þ ecb ! HO þ HO
Cꢀ
C
ꢀ
H2O2 þ O2 ! HO þ HO þ O2
Figure 5. Effect of recyclability of CeO2 on photocatalytic activity.
C
H2O2 ! 2 HO
O2 þ HOꢀ ! O2 þ HO
C
C
sedimentation of the dye around CeO2 resulting in decreased
activity.[31]
C
Dye þ OH ! degradation products
þ
Dye þ hvb ! oxidation products
2.6.6 Comparative study of photocatalytic degradation
using bulkCeO2 and nanoparticles
ꢀ
Dye þ ecb ! reduction products
Comparative studies related to the photocatalytic degradation
of trypan blue using our prepared CeO2 nanoparticles and
commercially procured bulk CeO2 are shown in Figure 6. The
photocatalytic reaction was carried out at a constant dye con-
centration (2 mgLꢀ1) and catalytic load (0.2 g/100 mL of CeO2).
From this experiment, it is clear that the photocatalytic activity
shown by our CeO2 nanoparticles is much better than for bulk
CeO2. This is because size and surface area play major roles in
photocatalytic activity.[26]
2.6.4 Effect of light source on photocatalytic activity
Figure 4d shows the effect of light sources on photocatalytic
degradation. Two different light sources are used, namely, sun-
light and UV light. From the figure, it is clear that photocatalyt-
ic degradation of the dye is greater in UV light than in sun-
light. This is due to the fact that UV light has a higher intensity
(lower wavelength or higher energy), so it can easily penetrate
the slurry, resulting in the formation of more radicals which in
turn increases the rate of photocatalytic degradation of the
azo dye.
2.6.5 Effect of recyclability of CeO2 for photocatalytic degra-
dation
Figure 5 shows the effect of recyclability of CeO2 in the photo-
catalytic degradation of trypan blue. One of today’s key indus-
trial wastewater treatment strategies focuses on the develop-
ment of green technologies. CeO2 recycling can be seen as
a good practice for sustainable industrial waste treatment.
Consequently, it is necessary to demonstrate whether the cata-
lyst can be reused after rounds of photocatalytic treatment.
The nanoparticles were recycled for consecutive use in the
trypan blue degradation process, which was repeated up to
three times. The photocatalytic reaction was carried out at
a constant dye concentration (5 mgLꢀ1) and catalytic load
(0.4 g/100 mL of CeO2). These studies indicate that the rate of
photodegradation of CeO2 in the first cycle is higher than the
subsequent cycles; this could be due to the aggregation and
Figure 6. Comparison of the photocatalytic degradation of trypan blue by
CeO2 nanoparticles and bulk CeO2.
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2.6.7 Kinetics of photocatalytic degradation
The plot of 1+log(optical density (O.D.)) versus irradiation
time is a straight line, as shown in Figure 7. This suggests that
the bleaching of dye by CeO2 follows a pseudo first-order rate
law. The rate constant was found to be 3.52ꢂ10ꢀ5 s-1 and was
calculated as follows: K (rate constant)=2.303ꢂslope, with the
following conditions: dye concentration=10 mgLꢀ1, catalytic
dosage=0.4 g/100 mL, pH 10. The data obtained for the kinet-
ics experiment are shown in Table 1.
Figure 8. Photochemical reduction of CrVI to CrIII using CeO2 nanoparticles.
Degradation was monitored by measuring the sample’s ab-
sorbance at 372 nm and 273 nm, which decreases gradually, in-
dicating the successful reduction of CrVI to CrIII as shown in
Figure 8.
The possible mechanism of the reduction of CrVI to CrIII
using CeO2 nanoparticles is shown below.
CeO2 þ hv ! CeO2 ðhþ þ eꢀÞ
ð11Þ
ð12Þ
ð13Þ
ð14Þ
ð15Þ
Figure 7. Kinetics of the photocatalytic degradation of trypan blue by CeO2
nanoparticles.
Cr2O72ꢀ þ 14 Hþ þ 6 eꢀ ! 2 Cr3þ þ 7 H2O
2 H2O þ 4 hþ ! O2 þ 4 Hþ
Table 1. Kinetics of trypan blue dye degradation by CeO2.[a]
þ
H2O þ hþ ! HO þ H
C
Time [min]
O.D.
1+log(O.D.)
0
15
30
45
60
75
90
105
120
2.43
2.12
1.95
1.69
1.48
1.35
1.23
1.05
0.89
1.39
1.33
1.29
1.22
1.17
1.13
1.09
1.03
0.95
CrVI þ H2O2 þ Hþ ! CrIII þ H2O þ O2
2.6.9. Detection of hydroxyl radicals
C
Hydroxyl radicals (HO ) have been proven to be the major
active species during the photocatalytic degradation reaction.
C
The amount of HO can be detected by photoluminescence
[a] Dye concentration=10 mgLꢀ1, catalytic dosage=0.4 g/100 mL, pH 10.
Measurement of optical density of dye solution at 592 nm.
C
(PL). The rate of formation of HO during the photocatalytic
degradation reaction could be detected by using a simple,
rapid, sensitive PL technique by using coumarin as a standard
C
probe. Coumarin reacts with HO to produce highly fluorescent
7-hydroxycoumarin at a signal of ~495 nm as shown in
Figure 9. In this method, catalyst (0.1 g) was dispersed in cou-
marin taken (50 mL of 10ꢀ3 m) in a borosil trough. Before irradi-
ation the solution was allowed to attain adsorption–desorption
equilibrium. This solution was irradiated with UV light with an
2.6.8 Reduction of CrVI to CrIII using CeO2 nanoparticles
Compared to CrIII, CrVI is more toxic, leads to adverse effects in
the human system, and may cause cancer.[32] It cannot be di-
rectly decomposed by microbes in the environment.[33] The re-
moval of CrVI from the environment via chemical or physical
adsorption has been previously reported.[34] The transformation
of CrVI to CrIII decreases its toxicity.[35] Here we report the pho-
tocatalytic degradation of K2Cr2O7 (1ꢂ10ꢀ3 m, pH 3.5) by CeO2
nanoparticles (0.2 g) upon treatment with UV light for 105 min.
intensity of 125 Wmꢀ2 [36]
Every 15 min, aliquots were drawn,
.
and the PL intensity was measured at 456 nm. The intensity in-
creased linearly with the irradiation time which indicates that
C
the formation of HO at the surface of CeO2 was proportional
to the irradiation time.[37]
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Table 2. Antibacterial activity of CeO2 nanoparticles towards P. aeruginosa
and S. aureus.
Zone of inhibition (diameter) [mm]
Group Treatment
P. aeruginosa
S. aureus
I
II
III
IV
Ciprofloxacin (10 mg/50 mL) 14.17ꢁ0.17
13.17ꢁ0.44
Not seen
Not seen
Not seen
CeO2 (500 mg/50 mL)
CeO2 (750 mg/50 mL)
CeO2 (1000 mg/50 mL)
3.33ꢁ0.33[**]
3.57ꢁ0.17[*]
4.50ꢁ0.29[**]
Values represent the mean ꢁS.E. for n=3 replicates. [*] p<0.05, [**] p<
0.01 as compared with the control group.
that interact with bacteria, resulting in the degradation of the
bacterial cell wall and eventual extermination.[38]
Figure 9. Phospholuminescence (PL) spectra for the detection of hydroxyl
radicals.
3. Conclusions
This paper reports the synthesis and characterization of CeO2
nanoparticles via solution combustion method using EDTA as
a fuel for the first time. XRD experiments confirm that the ob-
tained product is cerianite, cubic phase CeO2 with crystallite
size 35 nm. FTIR spectrum shows a strong band below
700 cmꢀ1 due to the CeꢀOꢀCe stretching vibration. The UV/Vis
spectrum shows a maximum absorption band at 302 nm. The
PL spectrum shows characteristic peaks of CeO2 nanoparticles.
SEM images clearly show a porous network with lots of voids,
while TEM images indicate spherical particles; the size of the
nanoparticles are found to be 42 nm. BET surface area and
pore diameter are found to be 163.5 m2 gꢀ1 and 2.9 nm respec-
tively. We have observed that CeO2 nanoparticles show signifi-
cant photocatalytic activity leading to the degradation of
trypan blue which follows pseudo first-order kinetics. CeO2
nanoparticles exhibit antibacterial activity against P. aeruginosa
2.7. Antibacterial activity of CeO2 nanoparticles
2.7.1 Agar well diffusion method
The stock solution of CeO2 nanoparticles was prepared by dis-
persing 2000 mgLꢀ1 in sterile water and making further dilu-
tions. Ciprofloxacin (500 mgLꢀ1 in sterile water) was used as
positive control and only sterile water was used as negative
control.
CeO2 nanoparticles were screened using the agar well diffu-
sion method on two different bacterial pathogens: Pseudomo-
nas aeruginosa and Staphylococcus aureus. We maintained the
positive standard’s concentration at 10 mg/50 mL, while varying
that of CeO2 nanoparticles from 500 mg/50 mL to 1000 mg/
50 mL for both bacterial pathogens. The obtained experimen-
tal data (Table 2) clearly show
that, as the concentration of
CeO2 nanoparticles increases, the
zone of inhibition also increases
in the case of P. aeruginosa. The
other
bacterial
pathogen,
S. aureus, did not show a zone of
inhibition due to the incomplete
dissolution of the compound
(Figure 10).
2.7.2 Broth dilution method
In the broth dilution method it
is clear that CeO2 nanoparticles
show antibacterial activity to-
wards P. aeruginosa (Figure 11).
The nanoparticles did not show
any activity towards S. aureus
when they were incubated for
24 h. A possible mechanism is
that the nanoparticles facilitate
Figure 10. Antibacterial activity of CeO2 nanoparticles using the agar well diffusion method. A) P. aeruginosa with
CeO2 (500, 750, and 1000 mg per 50 mL in well), s: Ciprofloxacin (standard, positive control), c: water (negative con-
the formation of free radicals trol); B) S. aureus with CeO2 (500, 750, and 1000 mg per 50 mL in well).
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Scheme 1. The obtained precipi-
tate of EDTA was washed several
times with water to remove Na+
ions present and dried at 808C for
1 h. The dried EDTA was used as
a fuel for the preparation of CeO2
nanoparticles.
Stoichiometric
amounts (1:1) of the oxidizer (2 g)
and fuel (0.8 g) were taken in
a trough, 10 mL distilled water was
added, and the mixture was stirred
for 10 min. The homogeneous
redox solution was preheated and
dehydrated on
a hot plate at
1508C. After dehydration, a gel
formed, and this was introduced
into a preheated muffle furnace
maintained at 4508C. Smoldering-
type combustion took place, and
within 3–4 min, the reaction pro-
ceeded to completion, forming
nanocrystalline CeO2.
4.3. Characterization. Powder XRD
data was recorded on an X’pert
PRO PANalytical X-ray diffractome-
ter (PANalytical, Almelo, The Neth-
erlands)
with
graphite-mono-
chromatized Cu-Ka (1.5418 ꢁ) radi-
ation. The FTIR spectrum of the
sample was collected using an
Alpha-P IR spectrometer (Bruker,
Billerica, USA). The absorption
spectrum and reduction spectrum
of CrVI to CrIII were measured on
a Lambda-750 UV/Vis spectrometer
(PerkinElmer, Waltham, USA). The
PL spectrum was measured using
Figure 11. Antibacterial activity of CeO2 nanoparticles using the broth dilution method. P. aeruginosa treated with
A) water (negative control); B) Ciprofloxacin (positive control); C) 200 mgmLꢀ1 CeO2; D) 400 mgmLꢀ1 CeO2 nano-
particles.
an RF-5301PC spectroflurophotometer (Shimadzu, Kyoto, Japan).
The BET surface area, that is, N2 adsorption–desorption measure-
ments of the samples were measured using a Tristar II surface area
and porosity instrument (Micromeritics, Norcross, USA). The surface
morphology was examined using an Ultra 55 SEM (Carl Zeiss, Jena,
Germany). TEM was performed on a JEM 1200 Ex microscope (Jeol,
Tokyo, Japan) operating at 100 kV.
in both agar well diffusion and broth dilution methods, and it
also actively reduces CrVI to CrIII in UV light at pH 3.5.
4. Experimental Section
4.1. Materials. All the chemicals used for synthesis were of analyti-
cal grade. Chemicals like (NH4)2Ce(NO3)6 and EDTA disodium salt
were purchased from Merck, India and were used without further
purification. Distilled water was used throughout the experiments.
4.4. Photocatalytic degradation of dye. Photocatalytic experi-
ments were carried out in a 150x75 mm batch reactor in the
month of August 2013 between 12–3 PM, in sunlight (750 Wmꢀ2
intensity) and in UV light (125 Wmꢀ2 intensity). An aqueous sus-
pension was prepared by adding a known amount of CeO2 nano-
particles (0.1–0.5 g) to a given concentration of trypan blue dye so-
lution (5–25 mgLꢀ1 in 100 mL). The pH of the solution was adjust-
ed by addition of either 0.1m NaOH or 0.1m H2SO4. During the
photocatalytic experiments, the slurry was stirred for uniform expo-
sure to light sources. A known volume of the exposed solution
(10 mL) was withdrawn at specific intervals of time (15 min), centri-
fuged (2000 rpm, 15 min) to remove the photocatalyst, and as-
sessed for extent of degradation using a spectrophotometer at
592 nm. Various parameters like effect of nanoparticle concentra-
tion, catalytic load, irradiation time, pH, nature of light, and recycla-
bility were also examined. After the completion of the photocata-
lytic degradation, the catalyst was removed by centrifugation
(2000 rpm, 15 min), washed with water, and dried in an air oven at
4.2. Preparation of CeO2 nanoparticles. (NH4)2Ce(NO3)6 and EDTA
disodium salt was used as an oxidizer and fuel respectively. To
remove the Na+ ions, EDTA disodium salt (10 mL of 1m solution)
was treated with HCl (5 mL of 2m), and the reaction is as shown in
Scheme 1. Conversion of disodium salt of EDTA to pure EDTA.
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1008C for 2 h. This oven-dried catalyst was used for another round
of degradation. This procedure was repeated twice, and degrada-
tion efficiency was tested each time.
4.5. Antibacterial activity by agar well diffusion method. Anti-
bacterial activity was screened by agar well diffusion method[39] for
bacterial pathogens (P. aeruginosa NCIM-2242 and S. aureus NCIM-
5022). These strains were purchased from National Chemical Labo-
ratory (NCL), Pune, India. Nutrient agar plates were swabbed using
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spective bacterial strains incubated for 24 h. By using a sterile cork
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Acknowledgements
T. N. Ravishankar wishes to acknowledge Jain University, India for
financial support to carry out the research.
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Keywords: antibacterial
· cerium oxide · nanoparticles ·
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photocatalysis · solution combustion
Received: August 26, 2014
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Revised: November 14, 2014
Published online on && &&, 0000
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FULL PAPERS
T. N. Ravishankar, T. Ramakrishnappa,*
G. Nagaraju,* H. Rajanaika
Nanoparticles for the environment:
CeO2 nanoparticles are competent pho-
tocatalysts for environmental applica-
tions because of their strong redox abil-
ity, nontoxicity, stability, and low cost.
We synthesized CeO2 nanoparticles
using a solution combustion method.
These show photocatalytic activity in
the degradation of trypan blue (a typi-
cal pollutant dye), antibacterial activity
against Pseudomonas aeruginosa, and
detoxifying activity as shown in the
reduction of CrVI to CrIII.
&& – &&
Synthesis and Characterization of
CeO2 Nanoparticles via Solution
Combustion Method for
Photocatalytic and Antibacterial
Activity Studies
ꢀ 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemistryOpen 2014, 00, 1 – 10
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ÞÞ
These are not the final page numbers!