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Enhanced photocatalytic performance of SnO2 doped with Fe2O3
Shengtian Huanga, Zhenghua Xiaob, Jianzhang Li*c, Junbo Zhongd and Wei Hue, Jinjin Hef
Key Laboratory of Green Catalysis of Higher Education Institutes of Sichuan, Sichuan University of Science and Engineering, Zigong, 643000, P. R. China
Keywords: SnO2; photocatalytic performance; doping; Fe2O3
Abstract. In this paper, SnO2 and Fe2O3 doped-SnO2 photocatalysts with different molar ratio of
Fe/Sn were synthesized by a parallel flow coprecipitation method. The photocatalysts prepared were
characterized by Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD) and UV/Vis
diffuse reflectance, respectively. The photocatalytic activity of photocatalysts prepared toward
decolorization of methyl orange (MO) solution was evaluated. Of all of the photocatalysts prepared
among the experimented compositions, Fe2O3 doped-SnO2 with 1.5%Fe possesses the best
photocatalytic activity.
Introduction
Tin oxide (SnO2) is an important metal-oxide, n-type wide band gap (3.6 eV at 300 K) semiconductor
with high exciton binding energy of 130 meV at room temperature [1, 2]. SnO2-based photocatalyst
has been paid much attention because of its physical and chemical characteristics [3]. However, the
photocatalytic performance of SnO2 should be further improved for practical use. A main limitation
of high photocatalytic performance in SnO2 semiconductors is the quick recombination of charge
carriers, because the electron-hole pairs generated in SnO2 semiconductor can be easily recombined
due to the direct band gap [4]. Among all the appoaches, modification of SnO2 by doping with metal
ions is an effective method to promote the photocatalytic performance. However, the influence of
Fe2O3 doped on the photocatalytic performance of SnO2 prepared by parallel flow coprecipitation has
been seldom concerned.
The purpose of this study is to examine the effect of Fe2O3 doped on the structure, surface texture,
response to the light and their relation with the photocatalytic activity of SnO2. In this paper, methyl
orange (MO) was chosen as the model azo dye.
Experimental
All chemicals (analytical grade reagents) were supplied from Chengdu Ke Long Chemical Reagent
Factory and used as received. Fe2O3-doped SnO2 was prepared by parallel flow coprecipitation
method using Fe (NO3)3 and SnCl4·5H2O with aqueous NH3·H2O+(NH4)2CO3. SnCl4·5H2O, desired
Fe(NO3)3 and HNO3 were completely dissolved in de-ionized water, the molar ratio of Fe/Sn is 0%,
0.5%, 1.0%, 1.5%, 2.0% and 3.0% respectively. On the other side, precipitant (NH3·H2O +
(NH4)2CO3) was dissolved in de-ionized water with the concentration 3+3 mol/L. Those two
solutions were dropped into the same reactor by peristaltic pump and agitated vigorously. The pH
value of precipitation reaction was around 8.5 by adjusting the flow velocity of two solutions. The
precipitate was filtered, washed with distilled water until no Cl- could be detected (using Ag
+). The
precipitate was dried by sprayer drying, and then calcined in air at 673 K for 2 h in a muffle furnace.
SnO2 photocatalyst prepared with different molar ratio of Fe/Sn (0%, 0.5%, 1.0%, 1.5%, 2.0% and
3.0%) were named as 0%Fe, 0.5%Fe, 1.0%Fe, 1.5%Fe, 2.0%Fe and 3.0%Fe, respectively. The
specific surface area analysis of photocatalysts was carried out by the BET method using
Advanced Materials Research Vols. 734-737 (2013) pp 2278-2281Online available since 2013/Aug/16 at www.scientific.net© (2013) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.734-737.2278
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 130.207.50.37, Georgia Tech Library, Atlanta, USA-17/11/14,15:31:22)
Autosorb-SSA-4200 (Builder, China). XRD patterns were recorded on a DX-2600 X-ray
diffractometer using Cu Kα (λ=0.15406 nm) radiation equipped with a graphite monochromator. The
X-ray tube was operated at 40 kV and 25 mA. The UV-Vis diffuse reflectance spectroscopy was
performed on a spectrometer (TU-1907) using barium sulphate as the reference.
Evaluation of the photocatalysis was performed according to the procedure given in the reference
[5]. All the photocatalytic decolorization experiments were performed in a SGY-II photochemical
reactor (Kai Feng HXSCI Science Instrument Factory, Kai Feng, China). The radiation source was
500 W high-pressure mercury lamp with a maximum emitting radiation of 365 nm, the lamp was
encapsulated in a cooling quartz jacket and positioned in the middle of the reactor, six quartz test
tubes were located around the lamp, the distance from the lamp to the quartz test tubes was 10 cm.
The initial concentration of MO solution was 10 mg/L. 50 mg of as-prepared photocatalyst was added
into 50 mL MO solution and reaction mixture was continuously aerated by a pump to provide oxygen
and for the complete mixing of the reaction solution. The decolorization reaction was performed at
room temperature. The pH value of the reaction solution was 7.0. After 1 hour, samples were
withdrawn and centrifuged (4000 rpm) to separate photocatalyst for analysis. The concentration of
MO was measured on a 756 PC spectrophotometer at 460 nm using Lambert-Beer law.
Results and discussion
The specific surface areas of the photocatalysts are shown in Table 1. As shown in Table 1, on doping
SnO2 with Fe2O3, the specific surface area tends to increase, it is plausible that the Fe2O3 doping
reduces SnO2 crystallization during the heat decomposition step and increases the specific surface
area. Among these six photocatalysts, 1.5%Fe sample has the highest BET surface area, while 0.0%Fe
has the lowest BET surface area. It is commonly acknowledged that the photocatalytic process is
mainly related to the adsorption and desorption of molecules on the surface of the photocatalyst. The
larger BET surface area the photocatalyst is, the more surface active sites emerge. The adsorbed
reactive species have more chance to react with adsorbed organic compounds [6], which is beneficial
to the photocatalytic activity.
Table 1 Specific surface area of photocatalysts
Photocatalyst 0%Fe 0.5%Fe 1.0%Fe 1.5%Fe 2.0%Fe 3.0%Fe
SBET (m2/g) 62 71 80 96 84 83
The XRD patterns of the as-prepared photocatalysts are shown in Fig.1.
0
400
800
1200
1600
2000
20 30 40 50 60
2 Theta (degree)
Inte
nsi
ty (
a.u
)
0%Fe
0.5%Fe
1%Fe
1.5%Fe
2%Fe
3%Fe
Fig.1. XRD patterns of photocatalysts
Advanced Materials Research Vols. 734-737 2279
As shown in Fig.1, all peaks are readily indexed to the tetragonal rutile phase of SnO2 (JCPDS card
No. 41-1445). No other peaks can be observed, indicating high purity of the as-prepared samples. The
presence of Fe2O3 was not observed; possibly due to the low dopant concentration used or the high
dispersion of Fe3+
in the lattice of SnO2 (The ionic radius of Fe3+
is smaller than the ionic radius of
Sn4+
).
UV/Vis diffuse reflectance spectra of SnO2 and Fe2O3 doped-SnO2 photocatalysts are shown in
Fig.2. UV/Vis diffuse reflectance spectra of Fe2O3 doped-SnO2 photocatalysts partially overlap, only
UV/Vis diffuse reflectance spectra of 0%Fe and 1.5%Fe were presented. As shown in Fig.2, 1.5%Fe
appears red shift, indicating narrow band-gap, which suggests that the response to the visible light
strengthens. The red shift and band-gap narrowing are primarily attributed to the substitution of Sn4+
ions by Fe3+
, which introduces new electronic states into the band of SnO2 to form a new lowest
unoccupied molecular orbital (interband trap site). Electrons that are excited from the valence band of
SnO2 by absorbing light photons can be captured by the interband trap site (Fe-O-Sn) in SnO2.
Electron trapping by this interband trap site also leads to a decrease in electron-hole recombination in
the doped photocatalysts [7].
0
20
40
60
80
100
200 300 400 500 600 700
Wavelength (nm)
Refl
ecta
nce (
%)
1.5%Fe0%Fe
Fig.2 UV-Vis diffuse reflectance spectra of photocatalysts
The photocatalytic activity of photocatalysts was compared and presented in Fig. 3
25
30
35
40
45
50
55
0 1 2 3
Atom concentration of Fe (%)
Deco
lori
zati
on
of
MO
(%
)
Fig.3 Removal of MO photolyzed for 60 min
2280 Resources and Sustainable Development
The photocatalytic activity of SnO2 and Fe2O3 doped-SnO2 photocatalysts is shown in Fig.3. As
shown in Fig.3, all Fe2O3 doped-SnO2 photocatalysts exhibit better photocatalytic activity than SnO2
and 1.5%Fe possesses the best photocatalytic performance among the experimented compositions.
These results suggest that Fe2O3 doping enhances the photocatalytic activity of SnO2 and that there is
an optimum loading of Fe2O3 in SnO2 particles. In this paper, high activity of 1.5%Fe may attribute to
the relative high surface area and good adsorptive capacity.
Conclusions
In summary, SnO2 and Fe2O3 doped-SnO2 photocatalysts with different molar ratio of Fe/Sn were
synthesized by a parallel flow coprecipitation method, which are only composed the tetragonal rutile
phase of SnO2. Doping Fe2O3 into SnO2 increases the BET surface area and decreases band gap of
doped SnO2 photocatalysts. When the molar ratio of Fe/Sn is 1.5%, removal of MO reaches 50% at 60
min, which improves more 23% than that of the pure SnO2. Doping with transition metal elements is
an effective way to enhance the photocatalytic performance of SnO2.
Acknowledgements
This project was supported financially by the Specialized Research Fund of Sichuan University of
Science and Engineering (No.2011PY04, Y201216), the Program of Science and Technology
Departmentof Sichuan province (No.2013JY0080), the Program of Education Department of Sichuan
province (No.11ZA127, No.12ZA089), the Project of Zigong city (No. 2011G042, No. 2012X07) and
the Opening Project of Key Laboratory of Green Catalysis of Sichuan Institutes of High Education
(No. LYJ1202, LYJ1208).
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DOI References
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