Study on the photocatalytic degradation of ammonia nitrogen in

aquaculture wastewater by Sn4+-doped nano-TiO2 under UV irradiation

Xiaocai Yu＊1,a, Pengfei Zhu 1,b, Min Zhang1,c Jiyao Guo1,dand Xv Zheng1,e

1College of Marine Environment Engineering, Dalian Ocean University, Dalian, Liaoning, 116023,

China

axiaocyu@dlou.edu.cn, bzhupengfei851@163.com, czhangmindlfu@yahoo.com.cn， d137454523@qq.com, e740747215@qq.com

Key words: Sn4+-doped nano-TiO2, Photocatalytic degradation, Ammonia nitrogen, aquaculture

wastewater

Abstract: The Sn4+

-doped nano-TiO2 particles with various amounts of dopant Sn4+

irons was

prepared by sol-gel method using tetrabutyl titanate(TEOT) as one of the primary raw materials at

different calcination temperatures (400-700˚C). The products were characterized by XRD and SEM,

which revealed that the crystal structure of Sn4+

-doped nano-TiO2 changes from anatase to rutile

with the calcination temperature increasing, and the nanoparticles diameter was around 10-30 nm.

The photocatalytic degradation of ammonia nitrogen in aquaculture wastewater was investigated by

using Sn4+

-doped nano-TiO2 under UV irradiation. The experimental results can be stated as follows:

when the ratio of dopant Sn4+

was 3% wt, the calcination temperature of Sn4+

-doped nano-TiO2 was

500 ˚C, the dosage of Sn4+

-doped nano-TiO2 was 0.8 g/L, respectively, if the reaction time may last

4h, the removal rate of ammonia-N was expected to reach 87.13%.

Introduction

Titanium dioxide has been proven to be one of the most effective photocatalysts for the

degradation of pollutants due to its high photosensitivity, stability under harsh conditions, non-toxic

nature [1, 2]

. To initiate such reactions, the catalyst surface is irradiated with light of sufficient energy

to span the semiconductor’s band gap. The electron/hole pairs are subsequently generated that may

initiate redox reactions at the catalyst surface. However, the high recombination rate of

electron/hole (e-/h

+) pair limits the application of TiO2

[3]. TiO2 is effective only under ultraviolet

irradiation (λ<380nm). Because solar light is comprised of less than 2% ultraviolet light, expensive

light sources must often be employed to activate TiO2 for these reactions to occur. Several studies,

therefore, have attempted to modify the surface of TiO2 as to extend the wavelength range of TiO2

into the visible region, and improve its efficiency of photocatalytic activity [4]

.

Doping TiO2 with transition metal ions has been frequently attempted not only to retard the fast

charge pair recombination [5, 6]

, but also to enable visible light absorption by providing defect states

in the band gap [7, 8]

. In spite of the different process have been reported in literature for

synthesizing of doped nano-TiO2, the sol-gel method has been considered a good approach to

fabricate doped nano-TiO2 particles because the chemical composition with a homogeneous

distribution can be easily controlled [9]

.

In this work, Sn4+

-doped nano-TiO2 particles with various amounts of dopant Sn4+

irons have been

synthesized by a sol-gel process at different calcination temperature. The photocatalytic activities

under UV light were also investigated by removing ammonia nitrogen in aquaculture wastewater.

Advanced Materials Research Vols. 347-353 (2012) pp 2351-2355Online available since 2011/Oct/07 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.347-353.2351

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Experimental

Chemical The reagents employed were tetrabutyl titanate (Tianjin Fuchen Chemical Factory,

China), as TiO2 source; tin chloride pentahydrate (SnCl4·H2O,99.0%) as dopant; dehydrated alcohol

(99.7%, China) as solvents; acetic acid glacial (99.5%, China) as catalyst. Ammonium sulfate was

used as simulation of ammonia nitrogen aquaculture wastewater. NaOH and HCL were used to

adjust pH value of the reaction solution. Phenol, sodium citrate, sodium hypochlorite, and hydrogen

peroxide were of analytical grade. Water was double distilled and filtered through a Millipore

membrane filer prior to use.

Sn4+-doped nano-TiO2 powder synthesis and characterization. Sn

4+-doped TiO2 particles were

synthesized by sol-gel method. Tetrabutyl titanate (5mL) was first added to dehydrated alcohol

(25mL), which were always under intense agitation, then continuing stirring for 1 hour, marked A

solution. Subsequently, a certain concentration of Sn4+

solution and acetic acid glacial (2mL) were

fully mixed together, marked B solution. Then, B solution was added to A solution slowly with

stirring. After finishing dropping, keep continuing stirring for 2 hours until a clear sol-gel solution

was formed. The Sn4+

-doped nano-TiO2 sol-gel was attained after aging 24 hours, and dried at

105˚C for 6 hours, which was then grounded into powder and introduced into a muffle furnace that

was preheated at the corresponding temperature. Thus, nanosized and white color Sn4+

-doped TiO2

crystallite was obtained. In this work, different Sn4+

/TiO2 catalysts can be prepared by changing the

concentration of dopant Sn4+

solution and calcination temperature.

The prepared Sn4+

/TiO2 catalyst was characterized by various techniques such as X-ray

diffraction(XRD), scanning electron microscope(SEM). The crystallinity of catalyst was determined

by XRD, which was purchased from Germany Bruker Company. The morphology and size of

particles were analysed by SEM, which was purchased from Japanese Electronics Company.

Simulation of ammonia-N aquaculture wastewater. A stock solution containing 100mg/L

ammonium-N was prepared by dissolving 0.4717g (NH4)2SO4 in distilled water, and diluting to

1000mL. Working solutions were prepared by suitable dilution of the stock solution.

Photocatalytic degradation of ammonium-N. 100mL of the ammonium-N solutions of desired

concentration were taken in the container. The prepared Sn4+

-doped TiO2 powder was added for all

the experiments. The pH value of the solution was adjusted at a desired level by NaOH or HCl.

Before irradiating the ammonium-N solution with UV, the solutions were fully stirred in the dark

for 35min, with the Sn4+

-doped TiO2 catalyst to achieve adsorption and desorption equilibrium. For

all the samples, the reduction in the initial ammonium-N concentration of the ammonium-N began

to happen. After a desired time irradiation with stirring, samples were taken and filtered, and

centrifuged to remove the catalyst powder before analysis. Then, a certain count of supernatant was

taken, by dropping little Indigo Blue, and placed in Water bath at 37˚C for 35min. Thus, the samples

were taken out, cooling prior to analysis.

. Sample analysis. The concentration of the ammonium-N in the samples was measured by

UV-visible spectrophotometer (Shanghai Spectrum, China), which was used for the determination

of color intensity in the range of 190-700 nm. The λmax value of ammonium-N is 640 nm.

Calibration based on the Beer-Lambert law was used to quantify the tested substances

concentration.

. Results and discussion

. Catalyst characterization

3.1.1 Morphology of Sn4+

-doped TiO2. The morphology of TiO2 was characterized by using

scanning electron microscopy (SEM). SEM images of Sn4+

-doped TiO2 are shown in Fig.1. As

displayed in fig.1, most of the Sn4+

-doped TiO2 particles were spherical and distributed evenly.

2352 Renewable and Sustainable Energy

Except a few content of particles reunited together, this may be ascribed to the fact that, Sn4+

-doped

TiO2 catalyst showed much higher Brunauer-Emmett-Teller (BET) surface area and surface activity,

another reason is due to Coulomb force between particles.

10 20 30 40 50 60 70 80

2-Theta-Scale

400 oC

500 oC

700 oC

600 oC

10 20 30 40 50 60 70 80

4 hours

3 hours

2 hours

2-Theta-Scale

5 hours

10 20 30 40 50 60 70 80

2-Theta-Scale

5 %

2 %

1 %

3 %

Fig.1. SEM image of Sn4+

-doped TiO2 powde (a) (b) (c)

Fig.2 XRD patterns of Sn4+

-doped nano-TiO2

3.1.2 XRD analysis. The crystal structure of Sn4+

-doped nano-TiO2 was determined by X-ray

diffraction (XRD). Fig.2 (a) illustrates a typical XRD spectrum of Sn4+

-doped nano-TiO2 prepared

at various calcinations temperatures (400°C, 500°C, 600°C, 700°C) with 2θ diffraction angles

between 10° and 80°, the results were compared with JCPDS database, which indicated that the

nano-TiO2 particles are fully anatase crystalline form at 400°C, and the rutile phase began to appear

at 500 ˚C, and the crystal structure was completely transformed to rutile (2θ= 27.38°, {110})at

700 °C. The primary peaks corresponding to anatase TiO2 appeared at 2θ= 25.38°, 37.90°, 48.12°

and rutile peaks were observed at 27.38°, 36.00°, 54.30°. Fig.2 (b) is the XRD pattern of different

calcined times at 400 ˚C, which shows that the anatase structure has been formed for 2 hours, and

the diffraction peak of anatase has no major significant changes with the calcined time increasing.

As can be seen, calcination temperature was significantly greater influence than the calcined time

on the crystalline state. Fig.2 (c) shows XRD patterns of Sn4+

-doped nano-TiO2 samples with

containing different dopant Sn4+

contents (1%, 2%, 3%, 5%) at the same calcination temperature of

500 ˚C. In addition, no Sn phase was found in XRD pattern, it can be concluded that Sn4+

irons

complete dissolved among the crystallite, that is to say, dopant Sn4+

may be highly dispersed on the

surface of TiO2.

Effect of different ratio Sn4+-doped on the efficiency of photocatalyst.

The effect of different ratio Sn4+

-doped into TiO2 on the photocatalytic degradation of ammonia-N

was studied. The results were showed in Fig.3(a). The experiments were carried out at different

doped amount of Sn4+

(0, 1, 2, 3, 5, 7 % wt), with a fixed NH4+

value of 30 mg/L and the same

reaction time of 1 hour. As shown in this fig, Sn4+

was helpful to conduct of photocatalytic

degradation, and the degradation rate increased with the content of doped Sn4+

increasing. However,

the degradation rate began to go down with the doped ratio of Sn4+

over 2 % wt.

0 2 4 6 8

20

22

24

26

28

30

32

34

36

38

40

42

Residual ammonia-N (mg/L)

Removal

Residual ammonia-N

Sn4+ content (%)

Removal (%)

18

20

22

24

400 450 500 550 600 650 700

20

25

30

35

40

45

50

55

60

Residual ammonia-N (mg/L)

Removal

Residual ammonia-N

Calcination Temperature (oC)

Removal (%)

12

14

16

18

20

22

24

0.4 0.6 0.8 1.0 1.2 1.4 1.6

28

30

32

34

36

38

40

42

44

46

48

50

52

Residual ammonia-N (mg/L)

Removal

Residual ammonia-N

Dosage of Sn4+-doped TiO

2 (g/L)

Removal (%)

14

16

18

20

22

0 1 2 3 4 5

20

30

40

50

60

70

80

Residual ammonia-N (mg/L)

Removal

Residual ammonia-N

Reaction time (h)

Removal (%)

6

8

10

12

14

16

18

20

22

24

(a) (b) (c) (d)

Fig.3 Effect of (a)different dopant Sn4+

, (b) calcination temperature, (c) dosage of Sn4+

-doped

nano-TiO2 and (d) reaction time on photocatalytic degradation

The reason may be due to that, when the doped amount of dopant Sn4+

is small, Sn4+

element can

produce an additional level of energy for the titanium dioxide, which makes electronic transition

easier. That is to say, the band gap of titanium dioxide is reduced by Sn4+

incorporation, thus

Advanced Materials Research Vols. 347-353 2353

increasing the photocatalytic activity of titanium dioxide. When the doped amount of Sn4+

exceeds a

certain limit (2%, under the conditions of this experiment), the photocatalytic activity of titanium

dioxide decreased, because of excessive accumulation of dopant Sn4+

in the surface of titanium

dioxide as electron and hole recombination center.

Effect of calcination temperature on the photocatalyst.

To study the effect of calcination temperature of Sn4+

-doped nano-TiO2 on the photocatalysis alone,

experiments were conducted at different calcination temperature of 400, 500, 600, 700 ˚C. As can

be seen from Fig.3(b)., the removal of ammonia-N increases firstly and again decreases with the

calcination temperature in preparing nano-TiO2 increasing. The removal reached up to the

maximum at 600˚C. This may be attributed to the fact that, when the calcination temperature is

lower, the anatase content of higher photocatalytic activity is less. The photocatalytic activity of

nano-TiO2 at 600 ˚C exceeded that of the others, the reason is that, when to 600 ˚C heat treatment,

the Sn4+

-doped nano-TiO2 is a small amount of rutile and anatase mixed phase. When the anatase

phase was mixed with a small amount of rutile phase, the cytalyst has higher photocatalytic activity

than a single phase of anatase or rutile.

Effect of dosage of Sn4+-doped nano-TiO2 on the removal of ammonia-N.

The effect of the dosage of Sn4+

-doped nano-TiO2 on the photocatalytic degradation of ammonia-N

was studied. The results were showed in Fig.3(c). The concentrations of the nano-TiO2 were varied

from 0.5 to 1.5 g/L, which were added into a batch of beakers, containing 100 mL NH4+

(30 mg/L)

solution. The samples were adjusted at the same reaction time. As shown in the fig, the optimal

dosage of Sn4+

-doped TiO2 was 0.8 g/L. The possible reason is that, as the initial dosage of TiO2

powder is increased, the amount of involved photolysis reaction of TiO2 particles is increased, and

the degradation rate is also increased. But the catalyst is added too much, due to solid particles

hinder the UV light, light scattering increase. Hence, the photodegradation efficiency is reduced.

Effect of reaction time on the removal of ammonia-N.

Experimental study on the effect of reaction time in the degradation of ammonia-N has been carried

out, and the result was shown in Fig.3(d)., which showed that the degradation rate of ammonia-N in

aquaculture wastewater was significantly changed with the time. That is to say, in other fixed

conditions, the degradation rate increased as time extending, and reached up to the maximum after 4

hours. With the time continuing to extend, the removal was no significant change.

Table 1 Design matrix and experimental results for the L9 (43) orthogonal array

Experiment Sn4+

content(%) calcination temperatures(˚C) reaction time (h) Sn4+

-doped TiO2 dosage (g/L) Removal /%

1 1 400 2 0.8 63.24

2 1 500 3 1.0 71.15

3 1 600 4 1.2 80.60

4 3 400 3 1.2 65.18

5 3 500 4 0.8 87.13

6 3 600 2 1.0 62.93

7 5 400 4 1.0 61.69

8 5 500 2 1.2 78.67

9 5 600 3 0.8 71.31

K1 214.99 190.11 204.84 221.68

K2 215.24 236.95 207.64 195.77

K3 211.67 214.84 229.42 224.45

R 3.57 46.84 24.58 28.68

2354 Renewable and Sustainable Energy

Optimization of reaction condition

On the basis of the results of above experiments, an orthogonal array experimental design was used

to select more efficient degradation condition. In this experimental design, four factors, including

dopant Sn4+

contents, calcination temperatures, Sn4+

-doped nano-TiO2 catalyst dosage and reaction

time, were studied and the reaction between factors was not considered, and every factor has three

levers to be optimized. The design matrix and experimental data were listed in Table 1. From the

mathematical processing of the data, some results can be concluded as follows. Firstly, the factor of

calcanition temperature for preparing Sn4+

-doped nano-TiO2 showed the most notable influence on

removal of NH4+

. Then, Sn4+

-doped nano-TiO2 dosage, reaction time were the relatively remarkable

factors, comparing with dopant Sn4+

content. Secondly, when 3%, 500˚C, 4 hours, and 0.8 g/L were

selected, respectively, for dopant Sn4+

content, calcanation temperature, reaction time, and

Sn4+

-doped nano-TiO2 dosage, 87.13% NH4+

removal was achieved under the optimized

parameters.

Conclusions

Sn4+

-doped nano-TiO2 particles with various amounts of dopant Sn4+

irons were successfully

synthesized by a sol-gel method at different calcanition temperature. It was found that the

Sn4+-doped nano-TiO2 particles are fully anatase crystalline form at 400°C, the little rutile phase

began to appear at 500 ˚C, and the crystal structure was completely transformed to rutile at 700 °C.

Sn4+

-doped nano-TiO2, as the photocatalyst, Show more excellent photocatalytic behavior in

comparison with the undoped TiO2 catalyst in removing ammonia nitrogen of aquaculture

wastewater under UV irradiation, which suggest that Sn4+

-doping may narrow the band gap of TiO2,

resulting in great enhancement of the photocatalytic activities. Furthermore, the optimization of

degradation conditions was studied by an orthogonal array experiment. When 3%, 500˚C, 0.8 g/L

and 4hours were selected, respectively, for Sn4+

-doping content, calcanation temperature,

Sn4+

-doped nano-TiO2 dosage, and reaction time, the removal rate of ammonia nitrogen in

aquaculture wastewater was expected to reach 87.13%.

Acknowledgment

This work has been supported by a grant from Natural Science Foundation of Liaoning Province

(20082137), Science Foundation of Education Department of Liaoning Province (2009A181) and

Dalian Science Fund (2009E12F64).

References

[1] A.C, Corma A and Garcia H，Phys. Chem. 10(2008), 769-783

[2] M.R. Hoffmann, S.T. Martin, and D.W. Bahnemann: Chem. Rev.95(1995), 69-96

[3] R.P.S. Suri, J. Liu, D.W. Hand, J.C. Crittenden, D.L. Perram, M.E. Mullins, Water Environ. Res.

65 (5) (1993) 665–673.

[4] D. Hufschmidt, D. Bahnemanna, J.J. Testa, C.A. Emilio, M.I. Litter, Photochem. Photobiol.

A-Chem. 148 (1–3) (2002) 223–231.

[5] Ikeda, S.; Sugiyama, N.; Pal, B.; Marci, G.; Palmisano, L.; Noguchi,H.; Uosaki, K.; Ohtani, B.

Phys. Chem. 2001, 3, 267.

[6] Paola, A. D.; Marci, G.; Palmisano, L.; Schiavello, M.; Uosaki, K.; Ikeda, S.; Ohtani, B. J. Phys.

Chem. B 2002, 106, 637.

[7] Fuerte, A.; Hernandez-Alonso, M. D.; Maira, A. J.; Martinez-Arias, A.; Fernandez-Garcia, M.;

Conesa, J. C.; Soria, J. Chem. Commun. 2001,2718.

[8] Xie, Y.; Yuan, C. Appl. Surf. Sci. 2004, 221, 17.

[9] T. Klimova, M.L. Rojas, P. Castillo, R. Cuevas, J. Ramírez, Micropor. Mesopor. Mater. 20 (1998)

293.

Advanced Materials Research Vols. 347-353 2355

Renewable and Sustainable Energy 10.4028/www.scientific.net/AMR.347-353 Study on the Photocatalytic Degradation of Ammonia Nitrogen in Aquaculture Wastewater by Sn4+-

Doped Nano-TiO2 under UV Irradiation 10.4028/www.scientific.net/AMR.347-353.2351

DOI References

[2] M.R. Hoffmann, S.T. Martin, and D.W. Bahnemann: Chem. Rev. 95(1995), 69-96.

http://dx.doi.org/10.1021/cr00033a004 [9] T. Klimova, M.L. Rojas, P. Castillo, R. Cuevas, J. Ramírez, Micropor. Mesopor. Mater. 20 (1998) 293.

http://dx.doi.org/10.1016/S1387-1811(97)00024-3