enhanced photocatalytic activity of cobalt-doped ceo2 nanorods

ORIGINAL PAPER

Enhanced photocatalytic activity of cobalt-doped CeO2 nanorods

N. Sabari Arul • D. Mangalaraj • Pao Chi Chen •

N. Ponpandian • P. Meena • Yoshitake Masuda

Received: 12 August 2012 / Accepted: 18 September 2012 / Published online: 28 September 2012

� Springer Science+Business Media New York 2012

Abstract In this paper, CeO2 and cobalt-doped CeO2

nanorods synthesized by surfactant free co-precipitation

method. The microstructures of the synthesized products

were characterized by XRD, FESEM and TEM. The

structural properties of the grown nanorods have been

investigated using electron diffraction and X-ray diffrac-

tion. High resolution transmission electron microscopy

studies show the polycrystalline nature of the Co-doped

cerium oxide nanorods with a length of about 300 nm and a

diameter of about 10 nm were produced. The X-ray Pho-

toelectron spectrum confirms the presence of cobalt in

cerium oxide nanorods. From BET, the specific surface

area of the CeO2 (Co-doped) nanostructures (131 m2 g-1)

is found to be significantly higher than that of pure CeO2

(52 m2 g-1). The Co-doped cerium nanorods exhibit an

excellent photocatalytic performance in rapidly degrading

azodyes acid orange 7 (AO7) in aqueous solution under

UV illumination.

Keywords Co-doped CeO2 nanorods � Chemical

synthesis � Surface area � Photocatalytic properties �AZO dyes

1 Introduction

One-dimensional (1D) nanostructured materials exhibit

many exclusive physical and chemical properties that are

quite different from the bulk state due to the enhanced sur-

face area to volume ratio and quantum confinement [1–6].

Cerium oxide (CeO2, ceria) is a face-centered cubic fluorite-

type crystal which is stable from room temperature to its

melting point. It has substantially fascinated researchers

due to its wide application as a promising material for cat-

alysts [7], oxygen sensors [8], UV blockers [9], etc. Various

techniques such as, precipitation, hydrothermal, reverse

micelles, sonochemical, sol gel method, etc. have been

employed to synthesize nanostructured ceria by using either

surfactants or costly chemicals as doping materials [10–16].

Among the different synthesis techniques, the precipitation

technique is an attractive one owing to its advantages of low

cost, simple process and easy scale-up. This method involves

simultaneous occurrence of nucleation, growth, coarsening

and agglomeration processes, which significantly affect the

size, morphology and properties of the products [17, 18].

Most of the previous reports were focused on the preparation,

growth and calcination effects of pure and doped cerium

oxide [19], but only a few have reported the growth and

influence of doping effect on the morphology of CeO2

nanostructures [20]. Moreover, doping cerium oxide doubles

its oxygen reserve and transfer capacity, greatly improving

its catalytic activities [21, 22]. The morphology of the cerium

oxide can significantly affects the photocatalytic applica-

tions. CeO2 nanorods are building blocks which are better

N. S. Arul (&) � D. Mangalaraj � N. Ponpandian

Department of Nanoscience and Technology,

Bharathiar University, Coimbatore 641 046, India

e-mail: [email protected]

P. C. Chen

Department of Chemical and Materials Engineering,

Lunghwa University of Science and Technology,

Taoyuan, Taiwan

P. Meena

Department of Physics, PSGR Krishnammal College

for Women, Coimbatore 641 004, India

Y. Masuda

National Institute of Advanced Industrial Science and

Technology (AIST), 2266-98 Anagahora, Shimoshidami,

Moriyama-ku, Nagoya 463-8560, Japan

123

J Sol-Gel Sci Technol (2012) 64:515–523

DOI 10.1007/s10971-012-2883-7

than nanoparticles due to their high aspect ratio enhance the

redox property by predominantly exposing the reactive

planes with well-defined active sites for better catalytic

reaction [23]. The investigation on cobalt-doped CeO2

nanorods has never been reported. Thus the prime aim of this

study was to increase the photodegradation of AO7 dyes by

doping CeO2 with cobalt ions.

This paper reports the data for photocatalytic activity of

CeO2 and Co-doped CeO2 nanorods synthesized by pre-

cipitation method at room temperature. In this synthesis

process, no surfactants, templates or organic solvents were

involved. The microstructures and morphology of the

individual nanorods were investigated. The effects of

cobalt ions doped cerium oxide on photocatalytic activity

of AO7 dyes were investigated in detail.

2 Experimental

2.1 Synthesis of CeO2 and Co-doped CeO2 nanorods

All the chemicals were obtained from Alfa Acer Inc., and

used without further purification. Cerium (III) nitrate

(Ce(NO3)3�6H2O) and cobalt (II) nitrate (Co(NO3)2�6H2O)

with laboratory purity were used as precursors and ammo-

nium hydroxide (NH4OH) was used as a co-precipitating

agent. The cerium precursor was kept fixed (0.5 M) and Co

doping concentration was varied (0.1, 0.3 and 0.5 M). Ini-

tially 0.5 M cerium nitrate solution was prepared and stirred

vigorously at room temperature. The cobalt nitrate solution

with different concentrations was added drop wise to the

prepared cerium nitrate solution to prepare three different

Co-concentrations. The pH was maintained at 11 by using

ammonia solution (28 %). The resultant colloidal solution

was sealed in a vessel to make a precipitate which was aged

at room temperature for 2 days. Finally the precipitates

were separated by centrifuging at 6,000 rpm and washed

several times with ethanol and de-ionized water to remove

the impurities. The final colloidal precipitate was dried at

90 �C for 2 h and then subjected to further characterization.

A similar procedure was adopted to obtain pure cerium

oxide nanoparticles.

2.2 Characterization techniques

Phase identification for the pure and Co-doped cerium oxide

nanorods was performed by X-ray powder diffractometer

(XRD) using Cu-Ka radiation (RIGAKU XRD/MAX-2200).

The microstructure of the Co-doped cerium oxide was

observed using a field emission scanning electron micro-

scope (FESEM) (JEOL JSM-6500) at 30 kV after sputter

coating the samples with gold. The morphology, particle size

and distribution were examined by transmission electron

microscopy (TEM) (JEOL JEM-2100F). Energy dispersive

X-ray analysis (EDAX) and selected-area electron diffrac-

tion (SAED) were also recorded in the TEM with an accel-

erating voltage of 200 kV. SAED pattern was studied to

check the crystalline nature of the synthesized sample.

Brunaur Emmett Teller (BET) nitrogen absorption plots

were used to study the change in the specific surface area of

the CeO2 samples on doping with different Co concentra-

tions. Brunaur Emmett Teller (BET) nitrogen adsorption

plots were used to measure the change in the specific surface

area of the CeO2 nanoparticles and nanorods. The photo-

degradation studies were done by measuring the absorbance

spectra SHIMADZU 3600 UV–Vis-NIR spectrophotometer.

2.3 Photocatalytic activity measurements

The measurement of photocatalytic activity of CeO2 and Co-

doped CeO2 materials was evaluated by analyzing its removal

efficiency of azodye acid orange 7 (AO7). The initial con-

centration of dye solution was 0.3 mM. Catalysts 10 mg were

suspended in 15 mL of AO7 followed by sonication for

10 min in the absence of light so that the equilibrium

adsorption on the surface of catalyst could be attained. Then

the solution was irradiated under UV light source of 2 mW.

The photodegradation studies were carried out by measuring

the maximum absorption of AO7 at 481 nm using SHIMA-

DZU 3600 UV–Vis-NIR spectrophotometer.

3 Results and discussion

3.1 Structural analysis

The crystal structure and phase purity of the prepared

samples were studied by X-ray diffraction. X-ray diffrac-

tion patterns of the as-prepared pure CeO2 and Co-doped

CeO2 nanostructures are depicted in Fig. 1. The major

peaks in all the four patterns are from CeO2 [JCPDS PDF

No 34-0394]. The diffraction pattern shows reflections

corresponding to (111), (200), (220), (311) and (222)

planes of CeO2-face centered cubic (fcc) fluorite structure

(space group: Fm3m). CeO2 with different Co-concentra-

tions shows well defined XRD peaks indicating the good

crystalline nature of the prepared material. Figure 2 shows

the average crystallite size and lattice parameters of pure

CeO2 and Co-doped CeO2 which were calculated from the

XRD diffracted peak at 28.589� corresponds to (111) plane

in [100] direction by using Scherrer formula.

It was revealed that the crystal size of CeO2 was reduced

after doping of cobalt. Comparing with the pure CeO2, the

crystal size of the Co-doped CeO2 nanorods decreases from

15 to 5 nm. This reduction in the crystallite size leads to an

increase in the specific surface area. The lattice parameter

516 J Sol-Gel Sci Technol (2012) 64:515–523

123

of the pure nanocrystalline cerium oxide is 5.427 A, which

is higher than that of its bulk counterpart (5.4113 A). The

increase in lattice expansion of small particles is due to the

increase of oxygen vacancies [24]. The decrease in the

lattice parameter with the increase of Co doping is in good

agreement with the effective ionic radii consideration. The

smaller Co2? (ionic radius = 0.745 A) occupies the posi-

tion of the larger Ce4? and (ionic radius = 1.098 A) as a

consequence, the unit cell volume decreases with increase

of the Co concentration [25, 26].

3.2 Morphological analysis of Co-doped CeO2

Field emission scanning electron microscopy (FESEM) was

used to obtain the morphology of the CeO2 and Co-doped

CeO2. From the FESEM images of the pure and Co-doped

ceria, it can be seen that the nanospheres undergo an evo-

lution from short nanorods to long nanorods on increasing

the concentration of Co. Figure 3a shows the FESEM image

of the pure cerium oxide synthesized by precipitation

method. The surface morphology shows the formation of

spherical particles only after 2 days of aging at room tem-

perature. Further the surface morphologies for the 0.1, 0.3

and 0.5 M Co-doped CeO2 samples prepared with the same

conditions are shown in Fig. 3b–d.

The nanorod formation is initialized on doping CeO2

with 0.1 M Co and it is shown in Fig. 3b. Further increase

in the Co-doping to 0.3 M leads to nucleation that results in

the growth of agglomerated nanoparticles, as depicted in

Fig. 3c. In our study, at equal molar concentration of cer-

ium and cobalt, the aggregates of nanoparticles are highly

terminated. Figure 3d shows the completion of the growth

and nucleation of nanorods at the equimolar concentration

of Co and CeO2. It is magnified and shown in the insert in

Fig. 3d, confirms the complete growth of Co-doped CeO2

1D nanorods. In order to confirm the optimized condition

of Co-doped cerium oxide nanorods, high mole concen-

tration (0.7 M) of Co was introduced into cerium precursor

and same process was carried out and finally FESEM was

carried out (Image not shown). The growth of CeO2

nanorods was terminated and agglomeration of nanoparti-

cles was observed. Because of the availability of sufficient

cobalt ion in the Ce precursor will ensure the growth of

nanorods was confirmed. So the equimolar concentration

(0.5 M) of CeO2 and cobalt provides sufficient ions for the

formation of nanorods. Under this condition, Ostwald rip-

ening exists, where smaller crystals add-up and join toge-

ther to form larger crystals which lead to the formation of

Co-doped CeO2 nanorods at the end of 2 days of aging at

room temperature.

3.3 Microstructural analysis of the nanorods

Transmission electron microscopy (TEM) and high resolu-

tion TEM (HRTEM) images offer additional insight into the

microstructure and morphology of the prepared Co-doped

cerium oxide nanorods. Figure 4a shows the HRTEM image

of the pure cerium oxide. The inset image shows the electron

20 30 40 50 60 70 80

(a)

2θ (degrees)

0.5M Co

0.3M Co

CeO2

(b)

(c)

0.1M Co

Inte

nsi

ty (

arb

.un

its)

(d)

οCeO2

οοοοοοο

111

ο

200

220

311

222

400 331

421

Fig. 1 (colour online) XRD pattern for the CeO2 sample a pure,

b doped with 0.1 M, c 0.3 M and d 0.5 M concentration of Co

0.0M 0.1M 0.3M 0.5M

5.37

5.38

5.39

5.40

5.41

5.42

5.43

Co Concentration (Mole)

Lat

tice

Par

amet

er (

A)

3

6

9

12

15

18

Crystallite size (n

m)

Fig. 2 Average crystal size and lattice parameter of cerium oxide

nanostructures as a function of different Co concentrations

J Sol-Gel Sci Technol (2012) 64:515–523 517

123

diffraction pattern which confirms the polycrystalline nature

of cubic cerium oxide. Clear facets are observed corre-

sponding to (111) planes.

The low and high resolution TEM and HRTEM images of

the as-prepared Co-doped CeO2 nanorods with equimolar

concentrations are represented in Fig. 4b–d. Figure 4b

shows a bright field TEM image of the as-prepared Co-doped

cerium oxide nanorods at low magnification. It is seen that

more than 80 % of the sample is made up of rod like struc-

tures. The magnified image in the insert in Fig. 4b shows the

nanorods with hexagonal structure. Figure 4c is the HRTEM

image of Co-doped single CeO2 nanorod with polycrystal-

line structure. A typical selected area electron diffraction

(SAED) pattern obtained for the CeO2 (Fig. 4a) and Co-

doped CeO2 nanorods is shown in Fig. 4c. The SAED pattern

is indexed according to cubic fluorite phase and it confirms

the polycrystalline nature of the prepared sample. The length

and width of the cerium oxide nanorods are determined from

TEM analysis as *100–300 nm and *10 nm respectively.

The aspect ratio (i.e., length/diameter) of the prepared

nanorods is *15. The lattice spacing value of 3.10 A were

identified as corresponding to (111) plane of CeO2, consis-

tent with the XRD results. The EDAX spectrum and the

corresponding elemental mappings recorded for sample

CeO2 nanoparticles and Co-doped CeO2 nanorods are shown

in Fig. 4e, f. The inset illustrates the actual distribution of Ce,

Co and O separately in the sample, with the Ce/Co ratio equal

to 22.81:2.99.

3.4 Surface area analysis

The surface area and porosity are essential properties of a

catalyst which determine its activity to apply for photocat-

alytic degradation applications. The pore architectures of the

catalysts control the transport phenomena and preside over

the selectivity in various catalyzed reactions. In addition to

FESEM and TEM studies, the pore nature of these CeO2 and

Co-doped CeO2 nanorods was confirmed by pore size dis-

tribution measurements, which were obtained by measuring

the adsorption–desorption isotherm and BJH methods.

Figure 5a, b shows the typical sorption isotherms and the

corresponding pore size distribution of CeO2 nanoparticles

(c)

(b)(a)

(d)

Fig. 3 FESEM images for as-prepared samples aged at room temperature for 48 h a pure, b 0.1, c 0.3 and d 0.5 M Co-doped with CeO2


123

and Co-doped CeO2 nanorods. It is seen that the isotherm is

of type IV, indicating the presence of mesoporous materials

according to the International Union of Pure and Applied

Chemistry (IUPAC) classification [27]. The type-IV iso-

therm with a hysteresis loop (H3) in the range of 0.8–1.0 P/Po

was obtained in our samples. The measured BET data indi-

cates that the synthesized Co-doped CeO2 nanorods possess

pores with mesoporous structures. A quantitative calculation

shows that our samples posses BET surface areas of nearly

52 and 131 m2 g-1 for CeO2 and Co-doped CeO2 nanorods

respectively. The enhanced surface area of the doped sam-

ples demonstrates that these samples are likely to be highly

efficient photocatalysts.

The calculated SSA versus Co-concentration for CeO2 with

various cobalt concentrations is plotted in Fig. 6. CeO2

particles form spherical in shape in the absence of Co ions.

Therefore, the contact areas between the particles are con-

sidered as negligible. The value of the SSA increases promi-

nently from 52 to 110 m2 g-1 on a small addition of 0.1 M Co

into CeO2. The addition of cobalt to CeO2 changes the shape

of the particle from the spherical form to nanorods. Further,

the increase of Co-doping to 0.3 and 0.5 M increased

the surface area to 129 and 131 m2 g-1 respectively. The

increase in the SSA may be due to the change in the shape of

the particle and the addition of Co on cerium oxide lattice in

accordance with the XRD results. Therefore, an appropriate

(e)

Ce Co Ce

(f)

(c)

3.10 Å

(d)

(b) (111)

(a)

Fig. 4 (colour online) a HRTEM image of pure CeO2; b–d TEM images for 0.5 M Co-doped cerium oxide nanorods with low and high

magnification images and inset corresponds to SAED pattern; e EDAX spectrum of CeO2 and f individual CeO2 nanorod doped with cobalt


123

concentration of cobalt in CeO2 assists in stabilizing the

crystal structure and produces nanorod like shapes with a high

SSA. Earlier, researchers achieved a high specific surface area

of 152 m2 g-1 by doping ceria with Pr [20]. In the present

work also, we have achieved comparatively similar SSA for

the ceria by significantly doping with cobalt at room tem-

perature. The nanorod morphology strongly influences the

catalytic response of the cerium oxide because of the increased

SSA and this may be very much useful for the catalytic

applications.

3.5 Growth mechanism

The formation of cerium oxide involves several complicated

reactions [28]. When ammonium hydroxide was added into

the precursor solution, Ce(OH)3 precipitate was formed

immediately due to the extremely low-solubility. In the

present case, the high alkaline environment favored the

oxidation of Ce(OH)3 to hydrated Ce(IV). Oxidation of Ce3?

and Ce4? in solution takes place at high pH [i.e.,

Ce3? ? H2O gives Ce4? ? H? ? e-] with a subsequent

hydrolysis to cerium hydroxide Ce(OH)4. The following

Eq. (1) shows the formation of CeO2.

CeðOHÞ4 ! CeO2 � 2H2O! CeO2 þ 2H2O ð1Þ

The influence of Co concentration on average grain size

(d), morphology and specific surface area (q) is

schematically explained in Fig. 7. The addition of 0.1 M

Co to cerium oxide starts the formation of nanorods from the

spherical shaped particles. When the concentration is

increased to 0.3 M, it is noticed that the proportion of

nanorods increases and a further increase of the cobalt

concentration to a value equal to that of cerium oxide (0.5 M)

leads to the maximum number of nanorods. Correspondingly

the SSA of the pure cerium oxide nanoparticles increases

from 52 to 131 m2 g-1 for the 0.5 M Co-doped cerium oxide

nanorods. The increase in the surface area of nanorods when

compared to that of spherical nanoparticles may be due to

higher grain size and may also be due to the pores which are

clearly visible in the TEM microstructure. The obtained

porous nanorods structure will serve as a very good candidate

for gas sensor and catalytic applications [20, 29].

3.6 Photocatalytic properties

Azodyes are manufactured universally and used in a vari-

ety of applications. They are a rich class of synthetic,

coloured, organic compounds widely contained in waste-

water generated from the textile and dyestuff industries and

pose a major threat to the surrounding ecosystems owing to

their non-biodegradability, toxicity and potential carcino-

genic nature [30]. In this study we have made an attempt to

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

50

100

150

200

Vo

lum

e A

dso

rbed

[cc

/g]

Relative Pressure, P/P0

Adsorption Desorption

(a)CeO

2 nanoparticles

10 100 10000.0000

0.0005

0.0010

Peak positions 2 nm-30 nm

Des

orp

tio

n D

v (d

) [c

c/A

/g]

Pore Diameter [A]

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00

50

100

150

200

250

Adsorption Desorption

Vo

lum

e A

dso

rbed

[cc

/g]

Relative Pressure (P/P0)

Co doped CeO2 nanorods (b)

10 100 10000.000

0.001

0.002

0.003

0.004

0.005Peak positions 2 nm-10 nm

Des

orp

tio

n D

v (d

) [c

c/A

/g]

Pore Diameter [A]

Fig. 5 Nitrogen adsorption–desorption isotherm of the prepared

various a CeO2 nanoparticles, b Co-doped CeO2 nanorods (inset of

a and b) corresponding BJH pore size distribution curve calculated

from the desorption branch

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.740

50

60

70

80

90

100

110

120

130

140

0.1 M Co in CeO2

0.3 M Co in CeO2

0.5 M Co in CeO2

Sp

ecif

ic s

urf

ace

area

-S

SA

(m

2 g-1)

Co concnetration (Mole)

CeO2

Fig. 6 Variation of specific surface area as a function of Co-

concentration


123

the study the degradation of azodyes using cerium oxide

nanorods.

The photodegradation activity of the pure CeO2 nano-

particles and Co-doped cerium oxide nanorods are mea-

sured for the AZO dye (AO7) for different time intervals

and the absorption spectra are shown in Fig. 8a, b. In the

present work, 0.3 mM of azodyes was dissolved in 15 mL

of double distilled water and 0.06 g of pure and Co-doped

cerium oxide was added with the as-prepared dye solution

for photocatalytic measurements. A UV light source of

2 mW with 365 nm wavelength was used for the experi-

ments. The intensity of the absorption spectra decreases

during the photodegradation of the azodye with increasing

time. The absorption spectra for the pure as-prepared dye

(black line), kept in darkness for 10 h (red line), and the

dye kept in UV illumination for 10 h (green line) are

shown in Fig. 8a, b. From the experimental results, it is

seen that there is no change in the intensity for the dye kept

in darkness for 10 h, but a slight decrease in absorption is

observed for the dye exposed to UV illumination for 10 h.

With this initial study, pure and Co-doped cerium oxide

nanorods (catalyst) were dispersed in the dye solution and

illuminated with UV light for different time intervals.

It is seen that in the decomposition of the dye, the Co-doped

CeO2 nanorods in the dispersed medium respond better when

compared to pure CeO2. This better degradation might be due

to the Co induced morphology of the CeO2 nanoparticles and

ρ =52m2 g-1

ρ = 110 m2 g-1

ρ =129 m2 g-1

ρ = 131 m2 g-1

Fig. 7 Schematic illustration for the formation of cobalt-doped cerium oxide nanorods and variation in specific surface area with the

morphology

300 400 500 600 700 8000.0

1.2

2.4

3.6

Wavelength (nm)

0.0

1.2

2.4

3.6

Catalyst - CeO2

(b)

Ab

sorb

ance

AO7 dye

dye in dark(10 hr)

dye kept in UV (10 hr)

dye + Catalyst + UV +1h






(a)

Catalyst - Co doped CeO2

Fig. 8 UV absorbance spectra at different time intervals for a AO7

dye, b Co-doped CeO2 nanorods with AO7 dye solution


123

the increase in the SSA. The increase in the surface area of the

Co-doped CeO2 helps to improve the absorption of photons.

The following Eq. (2) was used to estimate the rate of the

reaction during the photodegradation experiment:

InAo

At¼ kt ð2Þ

where Ao and At are corresponding absorptions measured

at different illumination times, k is the reaction rate and t is

the reaction time. The rate of the reaction k was calculated

for both the photodegradation experiments by drawing a

graph between absorption and time, ln Ao/At. The reaction

rates estimated from the slope of the linear fit are 0.142 and

0.213 h-1 for the pure and Co-doped cerium oxide

respectively. Figure 9 shows the changes in the photode-

composition of AO7 in the presence of Dye, CeO2 and Co-

doped CeO2 nanorods after irradiation with UV light. The

experimental results reveal that the photodegradation of

CeO2 nanorods can be improved by the inclusion of doping

Co ions. Due to the sufficient Co ions in CeO2 act as a

photo-generated hole and a photo-generated electron trap

which hinder the hole-electron pair recombination. The

photocatalytic activity of the Co-doped CeO2 nanorods

shows better response than pure CeO2 nanoparticles,

because of the effective separation rate of generated elec-

trons and holes in Co-doped CeO2 nanorods under UV

illumination. The crystal size and surface area also played a

major role in the photocatalytic activity of cerium oxide.

4 Conclusions

Co-doped 1D CeO2 nanorods were successfully prepared by

using a surfactant free precipitation technique at room tem-

perature. The Co acts as a structure directing agent and it

helps to form the nanorods in the equimolar concentration.

The structural properties clearly confirm the phases and the

presence of cerium oxide and cobalt. HRTEM analysis

reveals that the Co-doped CeO2 nanorods have a length of

100–350 nm and a diameter of *20 nm. The specific sur-

face area of the cerium oxide nanoparticles increases from

52 to 131 m2 g-1 for the Co-doped CeO2 nanorods. These

interesting results provide a basic understanding of the

influence of doping on the average grain size, the particle

morphology and specific surface area of the 1D nanostruc-

ture. From the photocatalytic measurements it is seen that

Co-doped cerium oxide nanorods exhibit a higher degrada-

tion property due to the influence of Co on its shape and SSA.

Acknowledgments One of the authors NSA would like to thank

Lunghwa University for offering Internship program, Mr. Shun Cho

and Ms. Koug Chen for their help in doing FESEM and Mr. Chih-Hua

Yu for helping to perform TEM measurements.

References

1. Gates B, Mayers B, Cattle B, Xia YN (2002) Adv Funct Mater

12:219–227

2. Li T, Yang SG, Huang LS, Gu BX, Du YW (2004) Nanotech-

nology 15:1479–1482

3. Huang Y, Duan XF, Wei QQ, Lieber CM (2001) Science 291:

630–633

4. Arul NS, Mangalaraj D, Chen PC, Ponpandian P, Viswanathan C

(2011) Mater Lett 65:2635–2638

5. Pan ZW, Dai ZR, Wang ZL (2001) Science 291:1947–1949

6. Zhang J, Jiang F, Zhang L (2004) J Phys Chem B 108:7002–7005

7. Murugan B, Ramaswamy AV (2007) J Am Chem Soc 129:

3062–3063

8. Jasinski P, Suzuki T, Anderson HU (2003) Sens Actuators, B

95:73–77

9. Zhang YW, Si R, Liao CS, Yang CH, Xiao CX, Kou Y (2003) J.

Phys. Chem. B 107:10159–10167

10. Pan C, Zhang D, Shi LJ (2008) Solid State Chem 181:1298–1306

11. Gao F, Lu Q, Komarneni SJ (2006) Nanosci Nanotechnol 6:

3812–3819

12. Gu F, Wang Z, Han D, Shi C, Guo G (2007) Mater Sci Eng, B

139:62–68

13. Zhang D, Fu H, Shi L, Pan C, Li Q, Yu YC (2007) Inorg Chem

46:2446–2451

14. Wu GS, Xie G, Yuan XY, Cheng BC, Zhang LD (2004) Mater

Res Bull 39:1023–1028

15. Tsunekawa S, Fukuda T, Kasuya A (2000) J Appl Phys 87:

1318–1321

16. Mai MX, Sun LD, Zhang YW, Si R, Feng W, Zhang HP, Liu HC,

Yan CH (2005) J Phys Chem B 109:24380–24385

17. Bugayeva N, Robinson J (2007) J Mater Sci Technol 23:237–241

18. Cushing BL, Kolesnichenko VL, Connor CLO (2004) J Chem

Rev 104:3893–3946

19. Zawadzki MJ (2008) J Alloys Compd 454:347–351

20. Yan L, Xing X, Yu R, Qiao L, Chen J, Deng J, Liu G (2007)

Scripta Mater 56:301–304

21. Yang J, Ferreira JMF (1998) Mater Res Bull 33:389–394

22. Tiejun C, Yuchao L, Zhenshan P, Yunfei L, Zongyuan W, Qian D

(2009) J Environ Sci 21:997–1004

23. Zhang TM, Li J, Li H, Li Y, Shen W (2009) Catal Today 148:

179–183

0 2 4 6 8 100

20

40

60

80

100

Dye + UV + 10h

Dye + CeO2 nanoparticles + UV+ 10h

Dye + Co doped CeO2 nanorods + UV + 10h

Ab

sorb

ance

(%

)

Time (hours)

Fig. 9 UV photodegradation at different time intervals for a AO7dye

(AO7), b CeO2, c Co-doped CeO2 nanorods


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24. Zhang F, Chan S-W, Spanier JE, Apak E, Jin Q, Robinson RD,

Irving Herman P (2002) Appl Phys Lett 80:127–129

25. May GJ (1978) J Mater Sci 13:261–267

26. Li L, Sasaki T, Shimizu Y, Koshizaki N (2009) J Phys Chem C

113:15948–15954

27. He Y, Li D, Xiao G, Chen W, Chen Y, Sun M, Huang H, Fu X

(2009) J Phys Chem C 113:5254–5262

28. Ferrari V, Llois AM, Vildosola V (2010) J Phys: Condens Matter

22:276002–276010

29. Han WQ, Wu LJ, Zhu YM (2005) J Am Chem Soc 127:12814–

12815

30. Elisangela F, Andrea Z, Fabio DG, Cristiano RM, Regina DL,

Artur CP (2009) Int Biodeterior Biodegrad 63:280–288


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enhanced photocatalytic activity of cobalt-doped ceo2 nanorods

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