Modern Research in Catalysis, 2013, 2, 127-135
http://dx.doi.org/10.4236/mrc.2013.24018 Published Online October 2013 (http://www.scirp.org/journal/mrc)
Synthesis of Chromium(III) Oxide Nanoparticles by
Electrochemical Method and Mukia Maderaspatana
Plant Extract, Characterization, KMnO4
Decomposition and Antibacterial Study
Rakesh1, S. Ananda1, Netkal M. Made Gowda2
1Department of Studies in Chemistry, University of Mysore, Mysore, India
2Department of Chemistry, Western Illinois University, One University Circle, Macomb, USA
Received June 14, 2013; revised August 5, 2013; accepted September 2, 2013
Copyright © 2013 Rakesh et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Chromium oxide nanoparticles were synthesized by the reduction of potassium dichromate solution with Mukia Made-
raspatana plant extract. In electrochemical methods, Cr2O3 nanoparticles were synthesized by two ways, using platinum
(Pt) electrodes and K2Cr2O7 solution with H2SO4 as medium in the first case. And chromium doped platinum electrode
(Pt/Cr) in presence of NaHCO3 solution in second case. The resulting Cr2O3 nanoparticles were characterized by X-ray
diffraction (XRD), Scanning electron microscopy (SEM), UV-VIS absorption and Fourier-transform infrared (FTIR)
spectroscopy. The enhancing influence of Cr2O3 nanoparticles as a catalyst for the decomposition of KMnO4 has been
studied. The antibacterial effect of Cr2O3 nanoparticles against E. coli was investigated. These particles were shown to
have an effective bactericide.
Keywords: Potassium Dichromate Solution; Cr2O3 Nanoparticles; Chromium Doped Platinum Electrode (Pt/Cr);
E. coli
1. Introduction
The study of fine and ultrafine particles has received in-
creasing interest due to new properties that material may
show when the grain size is reduced [1]. During the past
decades, considerable progress in the synthesis of nano-
particles has been achieved. Nanomaterials, particularly
transition-metal oxides play an important role in many
areas of chemistry, physics and material science [2]. In
technological applications, metal oxides have tradition-
ally been used in the fabrication of microelectronic cir-
cuits, sensors, piezoelectric devices, fuel cells, coatings
for the passivation of surface against corrosion, and as
catalyst [2]. In the emerging field of nanotechnology, a
goal is to make nanostructures or nanoarrays with spe-
cial properties with respect to those of bulk or single par-
ticles species. Metal oxides as nanoparticles can exhibit
unique chemical properties due to their limited size and
high density of corner or edge surface sites [2,3]. Among
metal oxides, special attention has been focused on the
formation and properties of chromia (Cr2O3) which is
important as heterogeneous catalyst [4], coating material,
wear resistance [5,6], advanced colorant [7], pigment [8]
and solar energy collector [9].
Various techniques for the synthesis of Cr2O3 nanopar-
ticles such as hydrothermal [10], sol gel [11], combustion
[12], precipitation-gelation [7], gel citrate [13], mech-
anochemical process [14], urea-assisted homogeneous
precipitation [15], gas condensation [16], and microwave
plasma have been developed [17]. Both chromium oxide
and supported chromium have been used as catalyst in
many reactions such as oxidation of toluene [18], ethane
dehydrogenation [12], and methanol decomposition [3].
In this study, we have synthesized chromium(III) oxide
nanoparticles by different methods and their catalytic
effects on the KMnO4 decomposition and antibacterial
activity have been reported here.
2. Experimental
Chromium oxide nanoparticles are synthesized by three
different methods and the comparative study for the
C
opyright © 2013 SciRes. MRC

RAKESH ET AL. 128
above synthesized nanoparticles is undertaken.
2.1. Method 1 (Biological Method)
Potassium dichromate from Rankem was used without
further purification. Mukia Maderaspatana plants were
collected from Hassan district and the edible part of the
whole plant was shade dried and pulverized using a me-
chanical grinder. The powdered plant material (50 g) was
extracted with methanol (200 ml) by soxhlet apparatus
for 24 hrs. The extract was evaporated using a rotary-
vaccum evaporator at 40˚C to provide dry extract. The
extract was kept at −20˚C until use. The preliminary phy-
tochemical analysis of the extract revealed the presence
of various bioactive components, such as alkaloids, fla-
vonoids, phenolics, aminoacids and glycosides [19]. An
amount of 10.0 g of potassium dichromate was dissolved
in 50 ml distilled water and stirred for 10 min. An orange
colored solution was obtained.
Preparation of Cr2O3 nanoparticles:
In an experiment, 20 ml of potassium dichromate solu-
tion was mixed with 20 ml of plant extract in a beaker
and stirred for 10 - 15 min. The colour of the solution
changed from orange to green indicating the formation of
chromium(III) oxide nanoparticles. The solution was
kept at room temp for evaporation of aqueous phase. The
green solid product was dried in hot air oven at 65˚C -
70˚C for an hour. The resulting solid was calcined at
650˚C - 700˚C for 3 hrs. The addition of potassium di-
chromate solution to the plant extract containing mild
reducing agents causes the reduction of orange dichro-
mate(VI) ions to green chromium(III) ions. As an exam-
ple, the reduction of Cr6+ to Cr3+ by reducing sugars re-
sulting in the formation of Cr2O3 nanoparticles is shown
below.
The chemical reaction takes place according to the
following mechanism (Scheme 1)
2
27
3
2
3RCHOCr O8H
3RCOOH2Cr4H O





Half equation for the reduction of dichromate(VI) ion
is
23
27 2
CrO14 H6e2Cr+7HO
 

Combining that with the half equation for the oxida-
tion of an aldehyde in aqueous condition
2
RCHOH ORCOOH2H2e

 
The reduction of Cr6+ to Cr3+ plays a main role in this
process and then Cr2O3 is generated.
3
223
2Cr+3HOCr O6H

 (Scheme 1)
2.2. Method 2 (Electrochemical Method in
Presence of K2Cr2O7 and H2SO4)
Chromium oxide nanoparticles are synthesized electro-
chemically using platinum electrodes. A solution of po-
tassium dichromate (0.3 M) was prepared. The electro-
chemical cell consists of reaction chamber a voltage po-
wer supply and platinum electrodes. The experiment was
performed with 20 ml volume of potassium dichromate
solution along with 5.0 ml of conc. H2SO4 as a support-
ing medium. A positive voltage of 12 V was applied us-
ing battery eliminator (Neulite India) and current output
of 70 mA - 90 mA. The experiment was run for 3 hrs
with continuous stirring. A change in colour from orange
to dark green was observed. The above solution was al-
lowed for the slow evaporation in a hot air oven at 100˚C
for 2 hrs. The dried solid which was obtained showed
positive results for sulphate test. Further, the solid was
calcined at 650˚C - 700˚C for removal of moisture and
sulfate as sulfur dioxide. The reduction equation is as
shown in equation below:

2272 42 424
3
22
2KCr O8HSO2KSO2CrSO
3O8H O




2423 2
3
4CrSO4Cr O12SO6O
2
2.3. Method 3 (Electrochemical Method in the
Presence of (Pt/Cr) and NaHCO3)
In this method a thin film of chromium was deposited
electrochemically on a platinum electrode (Pt/Cr) from
chromium nitrate solution (0.1 M). The preparation of
Cr2O3 nanoparticles was carried in a reaction chamber
containing 20 ml of NaHCO3 solution. Voltage power
supply of 12 V, current of 30 mA and Pt/Cr electrode as
anode, Pt electrode as cathode were used. The experi-
ment was run for 3 hrs with continous stirring at constant
temperature. The anodic dissolution of chromium to give
Cr3+ ions due to electrolytic reaction, which are electro-
chemically reacted with aqueous NaHCO3 to form Cr3+
oxides/hydroxides, which is shown in Scheme 2. The
synthesis takes place at the electrode-electrode interface
or close to the electric double layer [20]. The product
formed floats in the electrolyte solution the resulting gel
was filtered [21], washed several times with distilled
water till complete removal of unreacted NaHCO3 and
dried at 100˚C for dehydration and removal of hydrox-
ides. The dried compound was calcined for 3 hrs at
650˚C - 700˚C in muffle furnance in order to decompose
the hydroxides of chromium and to get chromium(III)
oxide.
The Electrochemical reaction takes place according to
the following mechanism:

RAKESH ET AL. 129
Cr Cr
3+
+3e
-
3NaHCO
3
+ 3e
- 3CO
2
+ 3Na + 3OH
-
Cr
3+
+ 3OH
- Cr(O H)
3
4Cr
3+
+ 6OH
-
2Cr
2
O
3
+ 3H
2
2Cr(OH)
3
Cr
2
O
3
+ 3H
2
O
(Scheme 2)
3. Results and Discussion
Characterization of the chromium oxide nanoparticles
was carried out by different techniques. UV-Visable
spectra were measured using (ELICO SL171) model
double beam spectrophotometer. FTIR spectra were re-
corded with Fourier-transform infrared instrument be-
tween 4000 cm−1 to 400 cm−1. The morphological prop-
erties of the Cr2O3 nanoparticles were examined by scan-
ning electron microscopy (SEM), X-Ray diffraction
(XRD) pattern was recorded with pananalytical X-ray
diffractometer using CuKα radiation (λ = 1.5406 Ǻ). The
IR spectra of chromium oxide synthesized from three
different methods are shown in Figures 1(a)-(c). It
shows that the characteristic bands are at 967 cm−1 - 1037
cm−1, 585 cm−1 - 641 cm−1 and 1046 cm−1 - 1085 cm−1.
Bands at 967 cm−1 - 1037 cm−1 are assigned to Cr=O
vibrations, 585 cm−1 - 641 cm−1 are assigned to Cr-O
vibrations and 1046 cm−1 - 1085 cm−1 are relatively as-
signed to Cr-O-Cr vibrations.
The X-ray diffraction pattern obtained for the chro-
mium oxide nanoparticles from three different methods
are as shown in Figures 2(a)-(c). The XRD spectrum
contains peaks that are clearly distinguishable. All of
them can be perfectly indexed to crystalline Cr2O3 not
only in peak position, but also in their relative intensity.
The peaks with 2θ values of 24.6˚, 36.3˚, 50.2˚ and
63.62˚ correspond to the crystal planes of (012), (110),
(024) and (214) of crystalline Cr2O3, respectively. An
average crystalline size, Dhkl was estimated using the
Debye-Scherrer equation given below for all X-ray dif-
fraction peaks.

hk1A0 cos
K
D




Where K is a shape factor which normally ranges be-
tween 0.9 and 1.0 (in our case K = 0.9), λ is the X-ray
wavelength, and β and θ are the half width of the peak
and half of the Bragg angle, respectively. Using the equa-
tion, the crystalline sizes of Cr2O3 nanoparticles which
were synthesized from method (1), electrochemical
method (2) and method (3) were found to be 65 nm, 79
nm and 41 nm respectively.
The UV-Visible spectrum of Cr2O3 is shown in Figure
3 which shows maximum absorption at 430 nm which is
a characteristic value for Cr2O3 as reported in the litera-
ture [22].
The morphological studies of synthesized Cr2O3 nano-
particles analyzed by scanning electron microscopy are
shown in Figures 4(a)-(c). Compared to three different
methods the nanoparticles were well separated and no
agglomeration was observed in method (3).
3.1. Chromium Oxide as a Catalyst in the Course
of KMnO4 Decomposition
It was elucidated that the more p-type character the solid
catalyst have, the more pronounced is the effect on the
reaction rate. Trying to compare the influence of chro-
mium oxide catalyst as a p-type semiconductor in the
course of other decomposition reaction will have great
value in view of the practical importance for oxygen evo-
lution. It has been suggested that its decomposition proc-
ess includes an electron transfer from one permanganate
ion to another with formation of stable 2
4
MnO

ions and
unstable MnO4 radicals [23]. Dowden [24] stated that the
most active oxide catalyst for oxygen abstraction is solid
oxides with vacancies in the d-orbital’s. It is found that
MnO2 enhances the rate of decomposition. Markowitz
and Boryta [25] suggested that the effect of metal oxide
on the decomposition can be attributed to the abstraction
of atomic oxygen. On the other hand, Freeman and Co-
workers [26] considered it to be due to a charge transfer
mechanism. Therefore, the reaction can be represented
for p-type catalyst as
4 oxide42
2
24 2
2oxide 2MnO2OMnOMnO
OMnO MnO2oxide


 
 
Where

is a positive hole in the oxide, Ooxide is an
oxygen atom abstracted by the oxide and MnO4 is a
radical. In this work an investigation has been carried out
to shed light on the reaction kinetics by which chromium
oxide can act as a catalyst for the decomposition of
KMnO4.
Effect of KMnO4 on the rate
The reaction was performed in the presence of 10 ml
of KMnO4 (0.0001 M, 0.00005 M, and 0.0002 M) taken
in three separate beakers consisting of 20.0 mg of Cr2O3
nanoparticles which were synthesized from three differ-
ent methods, namely method 1, method 2 and method 3.
The experiment was carried out at room temperature and
the rate of reaction was followed with respect to the
change in concentration of KMnO4 by using a spectro-
photometer. A plot of log%T verses time was recorded
where the rate of decomposition of KMnO4 increases in
the order of method 3 > method 2 > method 1, which is
shown in Table 1 and Figures 5(a)-(c). The results show

RAKESH ET AL. 130
(a)
(b)
(c)
Figure 1. (a) IR spectra of Cr2O3 nanoparticles synthesised using method (1); (b) IR spectra of Cr2O3 nanoparticles syn-
thesised by electrochemical method (2) using K2Cr2O7 and H2SO4 as medium; (c) IR spectra of Cr2O3 nanoparticles syn-
thesised by electrochemical method (3) using Pt/Cr electrode and NaHCO3.

RAKESH ET AL. 131
(a)
(b)
(c)
Figure 2. (a) XRD diffractogram of Cr2O3 nanoparticles synthesized using method (1); (b) XRD diffractogram of Cr2O3 nano-
particles synthesized by electrochemical method (2) using K2Cr2O7 and H2SO4 as medium; (c) XRD diffractogram of Cr2O3
anoparticles synthesized by e lec t r ochemic al method (3) using P t/Cr ele ctrode and NaHCO3. n

RAKESH ET AL. 132
(a)
Figure 3. UV-Vis absorption spectrum of Cr2O3 nanopar ti-
cles in aqueous solution.
(b)
(a)
(c)
Figure 5. (a) Effect of KMnO4 (0.0001 M) on the rate of its
decomposition; (b) Effect of KMnO4 (0.00005 M) on the
rate of its decomposition; (cfect of KMnO4 (0.0002 M) ) Ef
on the rate of its decomposition.
Table 1. Effect of KMnO4 concentration on its rate of de-
composition.
(b)
rate constant k × 10−5 s−1
[KMnO4]
Method 1 Method 2 Method 3
5.00 × 10−5 M6.90 8.44 8.06
1.00 × 10−4 M1.15 3.83 4.22
2.00 × 10−4 M1.05 1.91 3.45
that the catalytic activity was very high for the Cr2O3
nasynthe by meth, in whic size
f Cr2O3 is 41 nm, indicating smaller the size of Cr2O3
(c)
Figure 4. (a) SEM microgra2O3 nanoparticles syn- phs of Crnoparticles sizedod 3h the
thesized using method (1); (b) SEM micrographs of Cr2O3
nanoparticles synthesized by electrochem ical method (2) us-
ing K2Cr2O7 and H2SO4 as medium; (c) SEM micrographs
of Cr2O3 nanoparticles synthesized by electrochemical
method (3) using Pt/Cr and NaHCO3.
o
higher will be the catalytic activity.
Effect of Cr2O3 on the rate
The reaction was studied with varying amounts of

RAKESH ET AL. 133
Cr2O3 nanoparticles (10.0 mg, 20.0 mg and 30.0 mg),
keMnO (1.00 × 10−4 M)
co
2 3d by the three differ-
ntibacterial activity by Disc
cherichia Coli and Pseudo-
eping the concentration of K4
nstant. The rate increases with increase in the amount
of Cr2O3 nanoparticles, which is shown in Table 2 and
Figures 6(a) and (b). The catalytic activity was observed
greater for Cr2O3 synthesized by method 3 as its size is
lower than the other two methods.
3.2. Antibacterial Assay
The Cr O nanoparticles synthesize
ent methods were tested for a
diffusion method against Es
monas aregunosa. The pure bacterial culture was subcul-
tured on nutrient agar media. The activity was compared
against standard Gentamycin. The concentration of nano-
particles was 50 mg/ml and 50 µl of each solution was
Table 2. Effect of Cr2O3 nanoparticles on the rate of
KMnO4 decomposition.
rate constant k × 10−5 s−1
Amount of
Cr2O3 (mg) Method 1 Method 2 Method 3
10.0 0.38 2.30 0.78
20.0 1.15 3.83 4.22
30.0 9.59 27.6 28.7
(a)
(b)
Figure 6. (a) Effect of Cr2O3 (10.0 mg) on the rate of its de-
composition; (b) Effect of CrO (30.0 mg) on the rate of it
decomposition.
Chromium(III) oxide nanoparticles synthesized by bio-
chemical methods were characterized
Test Cr2O3 (M 1)Cr2O3 (M 2) Cr2O3 (M 3) Standard/+ve
2 3s
placed on a disc. After incubation for 48 hrs at 37˚C, the
different levels of zone inhibition of bacteria were meas-
ured. The zone inhibition in mm around Cr2O3 nanopar-
ticles is shown in Table 3 and Figures 7(a) and (b).
The values from the table indicate that the nano parti-
cles of Cr2O3 synthesized from all the three methods
show inhibiting effect towards different bacteria. How-
ever, the nano Cr2O3 (41 nm) synthesized from method 3
shows a very good inhibiting effect close to the standard.
The figure shows the zone inhibition of bacterial growth
on agar plates. Hence, the results clearly demonstrate that
the newly synthesized Cr2O3 nanoparticles were promis-
ing antimicrobial agents against bacteria.
4. Conclusion
logical and electro
by UV-Visible, IR, SEM and XRD. The nanoparticles
synthesized by Pt/Cr and NaHCO3 and by electrochemi-
cal method act as very good catalysts for KMnO4 de-
composition and as promising antibacterial agents.
Table 3. Zone of inhibition (mm) of Cr2O3 nanoparticles.
Organism (mm) (mm) (mm) control (mm)
Escherichia
coli 0.5 0.6 0.7 1.0
Pseudomonas
aregunosa 0.4 0.5 0.6 0.9
(a)
(b)
Figure 7. (a) Escherichia coli; (b) Pseudomonas aregunosa.

RAKESH ET AL. 134
5. Acknowledgements
One of the authors, Rakesh, acknowledges The Univer-
sity of Mysore and Jubilant Life Sciences Limited, Nan-
jangud, Mysore, for the grant of permission.
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