A simple preparation of carbon doped porous Bi2O3 with enhanced visible-light photocatalytic activity

Article abstract of DOI:10.1016/j.jallcom.2014.04.097

Carbon doped bismuth oxide (Bi₂O₃) with a porous structure is obtained by a simply calcination of bismuth nitrate pentahydrate (Bi(NO₃)₃.5H₂O) in glycol solution. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis absorption spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange (MO) in an aqueous solution under visible-light radiation (λ > 420 nm). The results show that carbon was incorporated into the lattice of Bi₂O₃. The absorption intensity of C-doped Bi₂O₃ increases in the region of 450-530 nm and the absorption edge has an obvious shift to long wavelength. The C-doped Bi₂O₃ exhibited much higher photocatalytic activity than the pure one due to the synergetic effects of the porous structure and the improved absorption in the visible-light region.

Full text of DOI:10.1016/j.jallcom.2014.04.097

Journal of Alloys and Compounds 608 (2014) 44–48
Contents lists available at ScienceDirect
Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jalcom
A simple preparation of carbon doped porous Bi2O3 with enhanced
visible-light photocatalytic activity
Gaopeng Dai a,b, , Suqin Liu a,b, Ying Liang a
⇑
a Department of Chemical Engineering and Food Science, Hubei University of Arts and Science, Xiangyang 441053, PR China
b Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices, Xiangyang 441053, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Carbon doped bismuth oxide (Bi2O3) with a porous structure is obtained by a simply calcination of bis-
muth nitrate pentahydrate (Bi(NO3)3Á5H2O) in glycol solution. The as-prepared samples were character-
ized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy
(XPS), and UV–Vis absorption spectroscopy. The photocatalytic activity was evaluated by the photocata-
lytic degradation of methyl orange (MO) in an aqueous solution under visible-light radiation (k > 420 nm).
The results show that carbon was incorporated into the lattice of Bi2O3. The absorption intensity of
C-doped Bi2O3 increases in the region of 450–530 nm and the absorption edge has an obvious shift to long
wavelength. The C-doped Bi2O3 exhibited much higher photocatalytic activity than the pure one due to the
synergetic effects of the porous structure and the improved absorption in the visible-light region.
Ó 2014 Elsevier B.V. All rights reserved.
Received 26 December 2013
Received in revised form 13 April 2014
Accepted 15 April 2014
Available online 24 April 2014
Keywords:
C-doped Bi2O3
Visible light
Photocatalysis
Calcination
1. Introduction
electron–hole recombination rate in the process of photocatalytic
reaction. Therefore, it is necessary to develop strategies to improve
Degradation of aqueous organic pollutants in wastewater
through photocatalysis has received increasing attention over the
last decades [1–3]. Although conventional TiO2 possesses excellent
photocatalytic activity and stability, it can only function under UV
light (ca. 4% of the solar spectrum). Therefore, many efforts have
been dedicated to develop visible light photocatalytic materials
for the better utilization of solar light [4–7]. One noteworthy strat-
egy is the development of the narrow band gap semiconductors as
visible light photocatalytic materials [8–11]. Among the various
narrow band gap semiconductors, bismuth oxide (Bi2O3) with band
gap varying from 2.1 to 2.8 eV is a prospective candidate [12–16].
The visible light photocatalytic activity of Bi2O3 has been widely
studied [12–18]. For example, Cheng et al. found that Bi2O3 dis-
plays much higher photocatalytic activity than N-doped P25 for
the degradation of methyl orange and 4-chlorophenol under visible
irradiation [16]. Muruganandham et al. reported the synthesis of
the honeycomb brushlike Bi2O3, which showed superior photocat-
alytic performance [17]. Wang et al. synthesized 3D flower-like
Bi2O3 microspheres with excellent visible-light-driven photocata-
lytic activities for the degradation of Rhodamine B [18]. However,
the application of pure Bi2O3 is still limited due to its high
the visible-light photocatalytic reactivity and efficiency of Bi2O3 for
the decomposition of organic pollutants.
Recently, it was reported that the doped Bi2O3 with other ele-
ments showed enhanced photocatalytic activity [19–22]. Li et al.
reported that dysprosium-doped Bi2O3 displays enhanced visible-
light photocatalytic performance due to the improved photoin-
duced charge separation rate [19]. Dai and co-workers reported
the fabrication of low Fe-doped Bi2O3 and its visible-light photo-
catalytic activity for the decolorization of chlorophenol [21]. Wu
et al. found that separation efficiency for electron–hole and visi-
ble-light photocatalytic activity were enhanced when Bi2O3 was
doped with praseodymium [22]. In this study, carbon doped
Bi2O3 was prepared via a simple calcination of Bi(NO3)3Á5H2O in
glycol solution. The prepared samples show high visible-light pho-
tocatalytic activity for the photodegradation of methyl orange
(MO) aqueous solution. To the best of our knowledge, this is the
first report on the preparation and visible-light photocatalytic
activity of C-doped Bi2O3.
2. Experimental
2.1. Sample preparation
⇑
Corresponding author at: Department of Chemical Engineering and Food
Science, Hubei University of Arts and Science, Xiangyang 441053, PR China. Tel.:
+86 710 3592609.
All reagents used in this study were of analytical grade and were purchased
from Shanghai Chemical Regent Factory of China without further purification. C-
doped Bi2O3 was prepared by a calcination method using Bi(NO3)3Á5H2O and glycol
as precursor. In a typical synthesis procedure, 1.5 g of Bi(NO3)3Á5H2O was dissolved
E-mail address: dgp2000@126.com (G. Dai).
http://dx.doi.org/10.1016/j.jallcom.2014.04.097
0925-8388/Ó 2014 Elsevier B.V. All rights reserved.

G. Dai et al. / Journal of Alloys and Compounds 608 (2014) 44–48
45
in 20 mL of glycol under magnetic stirring. Subsequently, the above solution was
transferred into an semi-closed alumina crucible with a cover, and then annealed
at 500 °C for 3 h with a heating and cooling rate of 10 °C minÀ1 to decompose
Bi(NO3)3 into Bi2O3. The reference sample, pure Bi2O3 without carbon doping, was
also prepared by a calcination method only using Bi(NO3)3Á5H2O as precursor and
all other experimental conditions were kept the same.
of doped carbon species [23] or the distortion of lattice induced
by the incorporation of carbon atoms into the surface and bulk
of Bi2O3 [24–26]. The average crystallite sizes of the pure and
C-doped Bi2O3 calculated by the Scherrer equation are 56.3 and
29.9 nm, respectively.
The morphologies of the as-prepared samples were investigated
using SEM. In contrast to the as-prepared pure Bi2O3 with smooth
surface (Fig. 2a), many porous appear on the surface of C-doped
Bi2O3 (Fig. 2b), suggesting that the presence of ethylene glycol
has a strong effect on the morphology of C-doped Bi2O3. The forma-
tion mechanism of the porous Bi2O3 is investigated by SEM analy-
sis of the products maintained at 550 °C for various times (Fig. 3).
After calcination for 20 min, Bi(NO3)3–glycol system burnt strongly
in the semi-closed alumina crucible (a quasi-closed system). An
extremely high temperature can be achieved within a very short
duration [27]. Then, Bi(NO3)3 was decomposed into Bi2O3 rapidly
and a part of glycol was sealed inside it. Thus, the surface of
Bi2O3 particles shows smooth and no holes can be observed as well.
After calcination for 40 min, the sealed glycol was decomposed
into carbon dioxide and water vapor, resulting in the formation
of holes on the surface of Bi2O3. With the increase of the time, more
holes formed, leading to the formation of porous C-doped Bi2O3
after calcination for 3 h. In contrast, in the absence of glycol, little
gas released and no holes formed in the pure Bi2O3.
The porous structure of C-doped Bi2O3 sample observed by SEM
was further studied by N2 adsorption/desorption analysis. Fig. 4
shows the N2 adsorption/desorption isotherms of the pure and C-
doped Bi2O3 samples. For C-doped Bi2O3, the physioadsorption iso-
therms can be classified as type IV in the IUPAC classification with
a distinct hysteresis loop observed in the range of 0.5–1.0P/P0,
which was characteristic of porous materials [28]. The BET surface
areas of the pure and C-doped Bi2O3 samples are 5.9 and 1.7 m2/g,
respectively.
2.2. Characterization
The X-ray diffraction (XRD) patterns, which were used to characterize the crys-
talline phases, were carried out on an X-ray diffractometer (D/MAX-RB, Rigaku,
Japan) using Cu Ka
radiation at a scan rate of 0.05° 2h sÀ1. The accelerating voltage
and the applied current were 40 kV and 80 mA, respectively. The morphology of the
sample was observed on a field emission scanning electron microscope (SEM) (Hit-
achi, Japan) with an acceleration voltage of 10 kV. X-ray photoelectron spectroscopy
(XPS) measurements were done on a VG ESCALAB 210 electron spectrometer using
Mg Ka radiation. All the binding energies were referenced to the C1s peak at
284.8 eV of the surface carbon. The UV–visible diffuse reflectance spectra of the
samples were obtained for the dry-pressed film samples using a UV–visible spectro-
photometer (UV-2550, Shimadzu, Japan). BaSO4 was used as a reflectance standard
in the UV–visible diffuse reflectance experiments.
2.3. Evaluation of photocatalytic activity
The photocatalytic activity of the samples was measured for the photocatalytic
oxidation of MO aqueous solution under visible-light at ambient temperature. In
detail, 0.1 g of the as-prepared catalyst powders was dispersed in a 25 mL of
4 Â 10À5 M MO aqueous solution in a 7.0 cm culture dish. Prior to illumination,
the resulting mixture was allowed to reach the adsorption–desorption equilibrium.
A 200 W xenon lamp with a 420 nm cutoff filter positioned 25 cm above the dish
was used as a visible-light source to trigger the photocatalytic reaction. The concen-
tration of MO was determined by an UV–visible spectrophotometer (UV-2550, Shi-
madzu, Japan).
3. Results and discussion
3.1. Phase structures and morphology
XRD was used to identify and determine the phase structure of
the as-prepared C-doped Bi2O3 powder. Fig. 1 shows a compari-
son of the XRD patterns of the pure and C-doped Bi2O3 samples.
As can be seen from this figure, the diffraction patterns of both
samples can be well indexed to the single monoclinic phase of
3.2. XPS analysis
The surface chemical composition and chemical states of the
samples studied were investigated by XPS. Fig. 5 exhibits the
high-resolution XPS spectra of the C 1s and Bi 4f regions of pure
and C-doped Bi2O3. In the case of the C-doped Bi2O3, the XPS peak
of C1s can be decomposed into three Gaussian peaks which cen-
tered at 280.7, 285, 288.9 eV, respectively. While, for pure Bi2O3
sample, only two Gaussian peaks were adopted to fit the profile.
The binding energy of 288.9 eV is associated with the carboxyl C
(OAC@O) groups. For the peak located at 285 is usually assigned
to elemental carbon. One of the greatest differences in the XPS
spectra is that the third fitted peaks at 280.7 eV for C-doped
Bi2O3 sample. The binding energy peak at 280.7 eV can be
ascribed to the formation of BiAC bond [29], indicating that C
substitutes oxygen in the lattice of Bi2O3. Similar metalAC bonds
were also observed in C-doped ZnO and C-doped TiO2, in which
the binding energy located 282.7 eV and 281 eV, respectively
[30,31]. Fig. 5B shows the Bi 4f spectrum of pure Bi2O3 and C-
doped Bi2O3. The binding energies of Bi 4f peaks (164.3 and
159.1 eV) in C-doped Bi2O3 increased to a higher value compared
with those of pure Bi2O3 (163.9 and 158.7 eV), suggesting that
some of the lattice oxygen atoms were replaced by carbon atoms
and doping C can lead to a decrease of electron density on Bi due
to the lower electronegativity of carbon compared to that of oxy-
gen [32,33].
well-crystalline
a-Bi2O3 according to the JSPDS file (No. 65-
2366), and no other diffraction peaks were found, indicating that
the C-doped sample maintains the crystal structure as pure Bi2O3.
It can be seen that there is no significant shift of XRD peak posi-
tion after carbon doped in the Bi2O3, but all diffraction peaks
became broadening in comparison with pure Bi2O3, and the peak
intensity decreases obviously, probably owing to the shield effect
b
a
3.3. UV–Vis diffuse reflectance spectra
25
30
35
40
2 theta
45
50
To study the optical response of pure and carbon doped Bi2O3
samples, the UV–Vis diffuse reflectance spectra were measured
(Fig. 6). Compared with the pure Bi2O3, the absorption edge of
Fig. 1. XRD patterns of pure (a) and C-doped Bi2O3 (b) samples.

46
G. Dai et al. / Journal of Alloys and Compounds 608 (2014) 44–48
Fig. 2. SEM images of pure (a) and C-doped Bi2O3 (b) samples.
20 min
40 min
500 oC
Bi(NO3)3
in glycol
500 oC
3 h
500 oC
Fig. 3. SEM images of C-doped Bi2O3 obtained by a calcination of Bi(NO3)3 in glycol solution at 500 °C for 20, 40 min, 1, and 3 h.
25
20
15
10
5
the C-doped Bi2O3 can expand to 800 nm with constant absorbance,
which is important for the solar energy application.
3.4. Photocatalytic activity
The photocatalytic performances of the pure and C-doped Bi2O3
samples were investigated by the decomposition of MO aqueous
solution under visible light irradiation. Under dark conditions (no
light irradiation), the concentration of MO did not change for mea-
surements on the Bi2O3 samples studied. Also, irradiation in the
absence of photocatalysts did not result in the photocatalytic
decolorization of MO. Therefore, the presence of both irradiation
and Bi2O3 sample is necessary for the efficient degradation of
MO. These results suggest that the decomposition of MO aqueous
solutions is caused by photocatalytic reactions on the Bi2O3 surface
under the visible light irradiation. The ratio of MO concentration C
and initial MO concentration C0 versus the degradation time was
shown in Fig. 7. It can be observed that commercial P25 exhibited
inefficient photocatalytic degradation with MO photodegradation
efficiency of 19% within 150 min. And approximately 42% of the
dye was removed by the pure Bi2O3, which is much slower than
that of C-doped sample. The enhanced photocatalytic activity of
C-doped Bi2O3 can be attributed to the synergetic effects of porous
structure, enhanced light-absorption and extended light-response
range caused by carbon-doping within the Bi2O3 lattice. The porous
materials possess larger specific surface area, which contributes to
more possible reaction sites on the photocatalyst surface, resulting
in the higher photocatalytic activity [34,35]. On the other hand,
b
a
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P )
0
Fig. 4. N2 adsorption and desorption isotherms for pure (a) and C-doped Bi2O3 (b)
samples.
the C-doped Bi2O3 has an obvious red-shift,1 and a conspicuous vis-
ible-light absorption shoulder around 450–530 nm can be observed,
which is consistent with yellow color characteristic of the C-doped
Bi2O3 sample (inset in Fig. 6). Furthermore, the photo-response of
1
For interpretation of color in Fig. 6, the reader is referred to the web version of
this article.

G. Dai et al. / Journal of Alloys and Compounds 608 (2014) 44–48
47
1.0
(A)
a
0.8
b
b
a
0.6
0.4
0.2
0.0
c
276
279
282
285
288
291
294
0
30
60
90
120
150
Binding Energy (eV)
Time (min)
Fig. 7. Photocatalytic activity of Degussa P25 (a), pure (b) and C-doped Bi2O3 (c)
samples.
a
b
(B)
4. Conclusions
C-doped Bi2O3 with porous structure have been successfully
synthesized by a simply calcinations of Bi(NO3)3 in glycol solution.
The C-doped Bi2O3 exhibits an obvious red-shift which occurs in
the absorption edge and presents significantly enhanced absorp-
tion in the visible-light region. The C-doped Bi2O3 exhibits excel-
lent photocatalytic activity for the photodegradation of MO
under the irradiation of visible light. This study provides a simple
one-step method to fabricate a high-performance photocatalyst,
which may open new possibilities to design semi-conductor mate-
rials for future applications.
156
160
164
168
Binding energy (eV)
Fig. 5. XPS spectra for the (A) C 1s and (B) Bi 4f of pure (a) and C-doped Bi2O3 (b)
samples.
Acknowledgements
This work was financially supported by the Natural Science
Foundation of Hubei Province (2012FFB01903), Research Program
of Hubei Province Department of Education (Q20132508), Science
and Technology Bureau of Xiangyang.
1.4
1.2
1.0
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0.8
0.6
0.4
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