Preparation and photocatalytic activity of Fe-Ce-N

tri-doped TiO2 catalysts

Yaoyao Wang1,a, Hong Xie1,b, Wei Zhang1,c, Yubin Tang1,d, Fangyan Chen*1,e

1School of Biotechnology and chemical Engineering, Jiangsu University of

Science and Technology, Zhenjiang, jiangsu 212018, China

a348331649@qq.com, b908599672@qq.com, c98745632@qq.com, dybbill@163.com, ecatchen1029@sohu.com ∗ Corresponding author

Keywords: Titania, photocatalyst, Fe-Ce-N co-doped, sol-gel method, UV light, daylight

Abstract: Fe-Ce-N tri-doped TiO2 photocatalyst was prepared by sol-gel method using tetrabutyl

titanate as precursor. The optimal doping amount and calcinations temperature were determined.

The prepared catalyst was characterized by X-ray diffraction (XRD) and UV-Vis diffuse reflectance

spectroscopy, and the photocatalytic activity was evaluated by means of the degradation for methyl

orange(MO) under UV light and daylight irradiation. The results indicated that the optimal doping

amount was 1.0% N, 0.25% Fe and 0.05% Ce, and the appropriate calcination temperature was

400℃. XRD analysis showed that TiO2 existed in anatase phase completely. UV-Vis adsorption

spectrum showed that Fe-Ce-N tri-doping resulted in a intense adsorption in the near UV and

visible-light region and a red shift in the adsorption edge from UV range to visible range of

400-500nm. The photocatalytic activity of Fe-Ce-N tri-doped TiO2 under UV and daylight

irradiation was very higher than that of bi-doped Fe-Ce-TiO2, Fe-N-TiO2, Ce-N-TiO2 and undoped

TiO2. The significantly higher activity of Fe-Ce-N tri-doped TiO2 may be due to the synergetic

effect of Fe, Ce and N in the tri-coped TiO2.

Introduction

Titania(TiO2) has been regarded as the most widely used, environment-friendly photocatalyst for its

high catalytic activity, chemical inertness, non-toxicity low cost and reuse, etc. At present, Titania

shows a broad application prospect in wastewater treatment, air purification and sterilization [1].

However, titanium dioxide exhibits photocatalytic activity under UV-light irradiation of

wavelengths less than 387nm due to its wide band gap of 3.2eV, resulting in only 2-4% of solar

energy being utilized by titania. In addition, low photo quantum efficiency resulting from high

recombination of photo-generated electrons and holes restricts the application of titania [2]. As a

result, various attempts have been made to improve optical absorption and photocatalytic activity

for the purpose of extending the visible-light absorption, suppress the recombination of

hole-electron pairs [3]. Of these attempts, the modification of titania by doping is an effective

method. The elements used to modify titania include transition metal ions, rare-earth metal ions and

nonmetal ions. The doping of nonmetal could narrow the band gap to intensify the response to

visible light and catalytic activity, whereas the doping of metal could trap temporarily the

photo-generated charge carriers to suppress the recombination of photo-induced electron-hole pairs

when migrating from the inside of the photocatalyst to the surface. It has been found that

modification of titania by co-doping of multi-elements can result in more visible-light response and

photocatalytic activity due to the cooperation action of the co-doping ions. At present, many studies

Advanced Materials Research Vols. 750-752 (2013) pp 1276-1282Online available since 2013/Aug/30 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.750-752.1276

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on co-doping of multi-ions have been reported, involving double metal [4], nonmetal-nonmetal [5],

metal-nonmetal [2, 6], tri-nonmetals [7, 8], nonmetal-nonmetal-metal [9-11] and tri-metals [12].

Nevertheless, to the best of our knowledge, there have been few reports on Fe-Ce-N tri-doped TiO2

photocatalyst. In the present work, ferric, cerium and nitrogen tri-doped TiO2 with high

photocatalytic performance was prepared using the sol–gel method. The photocatalytic activity of

the Fe-Ce-N tri-doped TiO2 was evaluated by means of the degradation for methyl orange(MO)

under UV light and daylight irradiation.

Materials and Method

Materials

Tetrabutyl titanate, anhydrous ethyl alcohol, acetic acid, urea, ferric nitrate nonahydrate, cerous

nitrate hexahydrate and methyl orange are all of analytical grade.

Preparation of the photocatalyst

The catalysts were prepared by sol-gel method using tetrabutyl titanate as the precursor. 10mL

deionized water, 20mL anhydrous ethylalcohol and 10mL acetic acid were mixed in a 250mL

three-neck flask to obtain solution A, and then a appropriate amount of dopants Fe(NO3)3, Ce(NO3)3

and CO(NH2)2 were dissolved in solution A. 17mL Ti(OC4H9)4 was added to the 40mL anhydrous

ethyl alcohol under stirring for mixing to obtain solution B. Solution B was added dropwise into

solution A and allowed to stir for 150min until the sols were formed. The gel was obtained after

ageing the sols at 50℃. The gels were dried fully under vacuum at 80℃ and then were ground to

obtain powdered samples. The obtained powder was calcined in a resistance furnace at 400℃ for 3h,

and then was cooled to room temperature. So Fe-Ce-N tri-doped TiO2 photocatalyst could be

obtained. The undoped TiO2 was prepared in the same way without addition of any dopants to

solution A.

characterization of photocatalyst

X-ray diffraction (XRD) pattern of the photocatalyst was obtained by a D8 ADVANCE

polycrystalline diffractometer (Bruker AXS, Germany) with Cu Kα irradiation, running at 40kV and

40mA, scanning from 10o-80

o at a rate of 2

o/min.

UV-Vis diffuse reflectance spectra of the photocatalyst were obtained using MPS-2000 UV-Vis

spectrophotometer supplied by Shimadzu, Japan

Measurement of photocatalytic activity

The photocatalytic activity was tested using methyl orange solution in SGY- IYB multi-purpose

photochemical reactor. The catalytic degradation under UV irradiation was performed using 300w

mercury lamp as light source, and catalytic degradation under daylight irradiation was carried out

using 350w Xenon lamp as light source. 0.1g of catalyst was added to the 200mL methyl orange

solution with the concentration of 10mg/L and the mixture was oscillated for 20 min with ultrasonic

radiation in the dark in order to disperse photocatalysts fully in methyl orange solution and to reach

adsorption equilibrium. Then the mixture was placed in a quartz vessel inside photochemical reactor

and was agitated using a magnetic stirrer at 25-28ºC. The light lamp was switched on. Aliquots of

mixture was taken out at periodic intervals during the irradiation, separated with centrifugation and

analyzed for the concentration of methyl orange at 465nm using visible spectrometer.

The photodegradation efficiency was calculated as ((A0-A)/ A0) ×100%, where A0 and A are the

absorbance of methyl orange solution at time, t=0 and any time, t, respectively.

Advanced Materials Research Vols. 750-752 1277

Results and discussion

Effects of N doping amount on photocatalytic activity

The doping amount of dopants was expressed as molar percentage of Fe, Ce, N with respect to Ti.

Degradation of MO in the presence of Fe-Ce-N tri-doped TiO2 with 0.5% Fe, 0.1% Ce and various

amount of nitrogen under UV irradiation was carried out and the results were shown in Fig.1. It can

be seen from Fig.1, Fe-Ce-N co-doped TiO2 has obviously higher activity than Fe-Ce co-doped

TiO2 free of N, indicating that N doping and Fe-Ce co-doping has synergistic effect in improving

the photocatalytic activity of TiO2. It is because N doping can reduce recombination rate of

photoinduced electrons and holes, prolong the life of photogenetrated charge carriers, and so as to

promote the photoctatlytic activity [13]. With the increasing N doping amount, the photolytic

efficiency of MO increased. The catalytic activity of TiO2 reaches the maximum at N doping

amount of 1.0%. While at higher N doping amount more than 1.0%, the photolytic efficiency of

MO decreased with increasing N doping amount. It may be because excess N doped in TiO2

become the recombination center of photo-generated electrons or holes and restrain the

photocatalytic activity [13]. Therefore, the appropriate N doping amount is 1.0%.

Effects of Fe doping amount on photocatalytic activity

Fig.2 depicted the photodegradation efficiency of MO in the presence of Fe-Ce-N tri-doped TiO2

with 1.0% N, 0.1% Ce and various amount of Fe under UV irradiation. As shown in Fig. 2, Fe-Ce-N

co-doped TiO2 has higher activity than Ce-N co-doped TiO2 free of Fe. It suggests that N doping

and Fe-Ce co-doping has synergistic effect in enhancing the photocatalytic activity of TiO2. This is

because doping Fe(III) can replace Ti(IV) in TiO2 lattice and increase the oxygen vacancy

anhydrous on the surface of TiO2, reducing the probability of recombination of electron-hole pairs.

So, photocatalytic activity improved evidently [14]. However, photocatalytic activity decreased as

Fe doping amount was more than 0.25%, which is because excessive Fe(III) became the

recombination center of the photoproduced electrons and holes. Therefore, the optimal doping

amount of Fe is 0.25%.

0 20 40 60 80 1000

20

40

60

80

100

free of N

N:0.50%

N:1.00%

N:1.25%

N:1.50%

N:1.75%

ph

oto

de

gra

dation

effic

ien

cy(%

)

time (min)

Fig.1 Effects of N doping amount on photocatalytic

activity

0 20 40 60 80 1000

20

40

60

80

100

free of Fe

Fe:0.05%

Fe:0.15%

Fe:0.25%

Fe:0.35%

Fe:0.50%

ph

oto

deg

rad

atio

n e

ffic

iency(%

)

time (min)

Fig.2 Effects of Fe doping amount on photocatalytic

activity

Effects of Ce doping amount on photocatalytic activity

The photodegradation efficiencies of MO in the presence of Fe-Ce-N co-doped TiO2 with 1.0% N,

0.25% Fe and various amount of Ce under UV irradiation were given in Fig. 3. As shown in Fig.3,

the photocatalytic activity of Fe-Ce-N tri-doped TiO2 enhanced significantly, compared with that of

Fe-N co-doped TiO2 without Ce. This is due to the synergetic effect of cerium and nitrogen, ferrum

in the co-doped TiO2. In addition, with increasing Ce doping amount, photocatalytic activity of

1278 Advanced Engineering Materials III

tri-doped TiO2 increased, because Ce can enter into TiO2 lattice and cause lattice deformation

resulting in escaping of the oxygen of TiO2 surface from lattice. The oxygen vacancy is,

consequently, formed, and became the capture center of photoinduced electrons, preventing

photogenerated charge carrier from recombining. So the photocatalytic activity of TiO2 is improved.

Nevertheless, at higher Ce doping amount more than 0.05%, it was likely to form a lot of Ti-O-Ce

bonds, which resulted in decreases in oxygen vacancy, and to make electrons and holes to

recombine easily [14]. So, it can be seen that the photocatalystic activity decreased. Therefore, the

appropriate Ce doping amount is 0.05%.

Effects of calcination temperature on photocatalytic activity

Photocatalytic efficiency of Fe-Ce-N tri-doped TiO2 calcined at 300-500℃ under UV irradiation

were shown in Fig. 4. As shown in Fig. 4, photocatalytic efficiency of tri-doped TiO2 calcined at

400℃, up to 99.2%, was evidently higher than that at the other temperature. Because at lower

calcination temperature, crystallization of TiO2 was not yet completed and lots of amorphous TiO2

with very poor photocatalytic activity occurred, resulting in poor catalytic activity of the tri-doped

TiO2. As the calcination temperature gradually raised, amorphous TiO2 particles transformed to

anatase TiO2 gradually and catalytic activity was enhanced [15]. Fig. 5 is the X-ray diffraction

(XRD) pattern of Fe-N-Ce tri-doped TiO2 calcinated at 400℃. As seen in Fig. 5, Fe-N-Ce tri-doped

TiO2 has a main peak at 2θ=25.2° which corresponds to the main peak of anatase TiO2 according to

JCPDSFile(No.21-1272), while the main peaks of rutile and brookite are at 2θ=27.4° and 2θ=30.8°.

Therefore rutile and brookite have not been detected, which suggested TiO2 existed in anatase phase

completely, resulting in the best photocatalystic activity of the tri-doped catalyst. The decreases in

photocatalytic activity at more than 400℃ may be attributed to decrease in specific surface area and

increases in crystal size resulting from sintering phenomenon at higher calcination temperature

[16-18].

0 20 40 60 80 1000

20

40

60

80

100

free of Ce

Ce:0.025%

Ce:0.04%

Ce:0.05%

Ce:0.075%

Ce:0.10%

ph

oto

de

gra

da

tio

n e

ffic

ien

cy(%

)

time (min)

Fig. 3 Effects of Ce doping amount on photocatalytic

activity

0 20 40 60 80 1000

20

40

60

80

100

300 oC

350 oC

400 oC

450 oC

500 oCp

hoto

degra

datio

n e

ffic

iency(%

)

time (min)

Fig.4 Effects of calcination temperature on photo-

catalytic activity

The catalytic activity of Fe-Ce-N tri-doped TiO2 under daylight irradiation

Prior to estimation of photocatalytic activity, UV-Vis diffuse reflectance spectra of pure TiO2

(undoped TiO2) and Fe-Ce-N tri-doped TiO2 were surveyed and depicted in Fig. 6. As shown in Fig.

6, the Fe-Ce-N co-doped TiO2 had a stronger adsorption in UV-Vis range and the adsorption edge

red shifted from UV range to visible range, which indicated dopants decreased band-gap of the

catalyst. This is due to the following factors: (1) when nitrogen was doped in TiO2, mixing of orbit

N 2p with orbit O 2p occurred, resulting in decrease in band gap energy of the TiO2 [19]. (2) Fe

Advanced Materials Research Vols. 750-752 1279

doping, as a doping of transitional metal ions, could shift adsorption edge from UV to visible light

without obvious change in band-gap of TiO2 [6]. Because Fe-Ce-N co-doped TiO2 adsorbs a larger

amount of visible light than pure TiO2, it could be a promising visible-driven photocatalyst.

The photolytic efficiencies of MO in the presence of Fe-Ce-N tri-doped TiO2 with 1.0% N,

0.25% Fe and 0.05% Ce under daylight irradiation were illustrated in Fig. 7. As shown in Fig.7, The

photolytic efficiencies of MO increased with increasing amount of catalysts and reach 86.7% after

180min as catalyst amount was 2.0g. This suggests that the Fe-Ce-N tri-doped TiO2 has high

catalytic activities for MO under daylight irradiation.

10 20 30 40 50 60 70 80 900

200

400

600

800

1000

1200

1400

1600

inte

nsity

/ o2θ

Fig.5 XRD pattern of co-doped TiO2 calcinated at

400℃

200 300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

Fe-Ce-N co-doped TiO2

undoped TiO2

ad

so

rban

ce

wavelength(nm)

Fig.6 UV-Vis diffuse reflectance spectra of

photocatalysts

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

0.5g

1.0g

1.5g

2.0g

2.5g

pho

tode

gra

datio

n e

ffic

iency(%

)

time (min)

Fig. 7 Catalytic activity of Fe-Ce-N tri-doped TiO2 under daylight irradiation

The comparison of photocatalytic activities of various co-doped TiO2

The photocatalytic degradation of MO by pure TiO2, Fe-Ce-TiO2, Fe-N-TiO2, Ce-N-TiO2 and

Fe-Ce-N-TiO2 under irradiation of UV light and daylight was depicted in Fig. 8 and Fig. 9,

respectively. As seen from Fig.8, the photocatalytic activity of tri-doped Fe-Ce-N-TiO2 is obviously

higher than that of undoped TiO2 or bi-doped Ce-N-TiO2, Fe-N-TiO2 and Fe-Ce-TiO2. Compared

with Fe-Ce-TiO2, Fe-N-TiO2, Ce-N-TiO2 and undoped TiO2, the catalytic activity of Fe-Ce-N-TiO2

under UV irradiation increased by 20.3%, 30.3%, 32.1% and 51.2%, respectively.

It can be seen from the Fig.9 that undoped TiO2 has a very poor daylight-induced catalytic

activity. This is due to the biggest indirect band-gap energy of about 3.2ev in undoped TiO2. When

bi-elements as Fe-Ce, Ce-N or Fe-N are doped into TiO2, daylight-induced photocatalytic activity of

1280 Advanced Engineering Materials III

the prepared samples slightly increased. The daylight-induced photocatalytic activity of Fe-Ce-N

tri-doped TiO2 was the best. The significantly higher activity under daylight irradiation of Fe-Ce-N

tri-doped TiO2 may result from the synergetic effect of Fe, Ce and N in the tri-doped TiO2. This is

due to the following factors: (1)The non-metallic N doping and transition metal Fe doping can all

make the light adsorption band edge transform to red shift and lead to visible light response. The

synergistic effect of N and Fe in co-doped TiO2 could make optical absorption of Fe-Ce-N-TiO2

enhance notably in the wavelength coverage of 400-500nm. (2)Fe and Ce could enter into the lattice

of anatase TiO2 and lead to lattice distortion, resulting in emergence of oxygen vacancy in TiO2

surface and reduction of Ti4+

to Ti3+

. Moreover, oxygen vacancy and Ti3+

can act as activity position,

thus enhancing photocatalytic activity [20, 21]. (3) N doping can not only enhance visible light

response, but also benefit the formation of oxygen vacancy in TiO2 surface, promoting the

photoctatlytic activity [22].

0

20

40

60

80

100

TiO2 Fe-N-TiO2 Fe-Ce-TiO2 N-Ce-TiO2 Fe-N-Ce-

TiO2

ph

oto

de

gra

da

tion

eff

icie

ncy(%

)

Fig.8 The photocatalytic activity of various catalysts

under UV irradiation

0

20

40

60

80

100

TiO2 Fe-N-TiO2 Fe-Ce-TiO2 N-Ce-TiO2 Fe-N-Ce-

TiO2

ph

oto

de

gra

datio

n e

ffic

iency(%

)

Fig.9 The photocatalytic activity of various catalysts

under the daylight irradiation

Conclusions

The tri-doped TiO2 with N, Fe and Ce was prepared by sol-gel method using tetrabutyl titanate as

precursor. Fe-Ce-N tri-doped TiO2 showed the highest photocatalytic activity when it was doped

with 1.0% N, 0.25% Fe and 0.05% Ce and was calcined at 400℃.

X-ray diffraction analysis shows that TiO2 existed in anatase phase completely, UV-Vis

adsorption spectroscopy analysis indicated that the co-doped TiO2 had a stronger adsorption in the

UV-Vis range and the adsorption edge red shifted from UV range to visible range, showing higher

adsorption in the visible light range of 400-500nm.

The tri-doped Fe-Ce-N-TiO2 has high UV light-driven and daylight-induced activity. 99.2% and

86.7% of methyl orange with concentration of 20mg/L can be degraded by Fe-Ce-N-TiO2 under UV

and daylight irradiation, respectively.

Under UV irradiation, the catalytic activity of Fe-Ce-N-TiO2 increased by 20.3%, 30.3%, 32.1%

and 51.2%, respectively, compared with Fe-Ce-TiO2, Fe-N-TiO2, Ce-N-TiO2 and undoped TiO2.

Under daylight irradiation, the catalytic activity of Fe-Ce-N-TiO2 increased by 43.0%, 35.5%,

40.0% and 81.2%, respectively. The significantly higher activity of Fe-Ce-N tri-doped TiO2 may be

due to the synergetic effect of Fe, Ce and N in the tri-coped TiO2.

Advanced Materials Research Vols. 750-752 1281

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