MBiO2Cl (M=Sr, Ba) as novel photocatalysts: Synthesis, optical property and photocatalytic activity

Article abstract of DOI:10.1016/j.materresbull.2014.11.032

Two Bi-based compounds SrBiO₂Cl and BaBiO₂Cl were successfully synthesized by a solid-state reaction and investigated as new photocatalysts for the first time. Their microstructures and optical properties were characterized by XRD, S

Full text of DOI:10.1016/j.materresbull.2014.11.032

Materials Research Bulletin 62 (2015) 206–211
Contents lists available at ScienceDirect
Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
MBiO Cl (M
property and photocatalytic activity
¼
Sr, Ba) as novel photocatalysts: Synthesis, optical
2
Hongwei Huang *, Shuobo Wang, Yihe Zhang *, Xu Han
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials
Science and Technology, China University of Geosciences, Beijing 100083, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 12 June 2014
Received in revised form 20 October 2014
Accepted 14 November 2014
Available online 17 November 2014
Two Bi-based compounds SrBiO Cl and BaBiO Cl were successfully synthesized by a solid-state reaction
2
2
and investigated as new photocatalysts for the first time. Their microstructures and optical properties
were characterized by XRD, SEM and DRS. The band gaps of SrBiO Cl and BaBiO Cl were separately
2
2
determined to be 3.52 and 3.71 eV, and their ECB and EVB were also estimated. The photocatalytic activities
of the as-prepared samples were evaluated by photodecomposition of rhodamine B (RhB) in aqueous
solution. The results revealed that both SrBiO
2
Cl and BaBiO
2
Cl can be used as effective photocatalysts
Cl, which was also
Keywords:
under UV irradiation, and SrBiO Cl exhibits a higher photocatalytic activity than BaBiO
2
2
Semiconductors
Layered compounds
Catalytic properties
verified by the PL spectra. Terephthalic acid photoluminescence probing technique (TA-PL) demonstrated
ꢀ
that OH radicals serving as active species play an important role in photooxidative degradation of RhB
ꢀ
over SrBiO
SrBiO
2
Cl and BaBiO
2
Cl. Moreover, a larger amount of OH radicals generation was observed over
2
Cl, which is in agreement with its higher photocatalytic activity.
ã 2014 Elsevier Ltd. All rights reserved.
1. Introduction
In this work, two Bi-based compounds SrBiO
2
Cl and
BaBiO Cl with layered structures were successfully synthesized
2
Semiconductor photocatalysis has received ever increasing
by a solid-state reaction. Their photocatalytic activities were
investigated by photodegradation of rhodamine B (RhB) for the
first time. The photocatalytic efficiency of SrBiO Cl and BaBiO Cl
2 2
attention owing to its unique energy conversion ability and strong
oxidation capacity for pollutants [1–3]. Though numerous semicon-
ductor photocatalysts have been discovered until now, exploration
of new photocatalytic materials is very active in this field [4–7].
Recently, layered Bi-based photocatalytic materials were found
displaying excellent photocatalytic activity for degradation of
was compared by quantitative detection of the amount of the
ꢀ
active species ( OH radicals). Moreover, their microstructures
and optical properties were also characterized.
2. Experimental
organic contaminants. These photocatalysts include Bi
Bi MoO [9], BiPO [10], Bi CO [11], BiOX (X Cl, Br, I) [12] and
other newly discovered bismuth photocatalysts [13–18]. Among
them, the BiOX (X Cl, Br, I) series exhibit high photocatalytic
activity and interesting structure–property relationship. In their
2 6
WO [8],
2
6
4
2
O
2
3
¼
2.1. Synthesis
¼
All the chemicals from commercial source were used as received,
2+
crystal structures, the (Bi
2
O
2
)
layers and halogen ion slices are
without further purification. SrBiO
sizedbya solid-statereaction.The raw materialsofSrCO
2
Cl and BaBiO
2
Cl were synthe-
, BaCO and
alternatively stacked to form the three-dimensional configuration.
It is believed that in BiOX the permanent electric fields between
3
3
BiOCl were mixed and ground in stoichiometric proportions, then
ꢂ
the [Bi
2
O
2
] layers and [X] slabs can greatly facilitate the separation
gradually elevated to sintering temperatures of 700 C and kept at
ꢁ
+
of photogenerated electron (e )–hole (h ) pairs, promoting the
high-efficient photooxidation degradation of organic contami-
nants. Therefore, it is very meaningful to explore other layered Bi-
based compounds as new photocatalysts.
this temperature in air for 24 h. This calcination procedure was
repeated three times to achieve a complete reaction.
2.2. Characterization
X-ray diffraction (XRD) patterns were recorded by a Bruker
D8 ADVANCE X-ray diffractometer with Cu K
a radiation. A
*
Corresponding authors.
E-mail addresses: hhw@cugb.edu.cn (H. Huang), zyh@cugb.edu.cn (Y. Zhang).
S-4800 scanning electron microscope (SEM) was used to observe
http://dx.doi.org/10.1016/j.materresbull.2014.11.032
025-5408/ã 2014 Elsevier Ltd. All rights reserved.
0

H. Huang et al. / Materials Research Bulletin 62 (2015) 206–211
207
Fig. 1. (a) Unit cell of SrBiO
2
Cl or BaBiO
2
Cl, (b) (Bi
2
O
2
)2+ layer and (c) crystal structure of SrBiO
2
Cl or BaBiO
2
Cl along a–c plane.
2 2
Fig. 2. XRD patterns of as-synthesized (a) SrBiO Cl and (b) BaBiO Cl.
ꢀ
the morphology and microstructure of the as-prepared photo-
catalysts. UV–vis diffuse reflectance spectra (DRS) with collected
range 200–800 nm were performed by a PerkinElmer Lambda
solution) can reacts readily with OH to form a highly fluorescent
2-hydroxyterephthalic acid (TAOH) [19]. The fluorescence emis-
sion spectra at 425 nm were recorded by a Hitachi F-4600 fluores-
cence spectrophotometer with the excitation wavelength of
315 nm. This TA-PL technique was similar to the former photo-
degradation experiment only that RhB solution was replaced by TA
aqueous solution.
35 UV–vis spectrometer. Photoluminescence (PL) emission spectra
were measured on a JOBIN 10 YVON FluoroMax-3 fluorescence
spectrophotometer with a 150 W Xe lamp used as the lamp under
the excitation wavelength of 254 nm.
2.3. Photocatalytic evaluation
2 2
The photocatalytic activities of SrBiO Cl and BaBiO Cl were
tested by photodegradation of rhodamine B (RhB) under UV light
irradiation of a 300 W high-pressure mercury lamp. The detailed
procedure is as follows: 50 mg of photocatalyst was dispersed into
ꢁ
6
5
0 mL of 5 ꢃ10 M RhB solution. Before irradiation, the suspen-
sion of SrBiO Cl or BaBiO Cl photocatalyst and RhB was vigorously
2
2
stirred in the dark for 1 h to reach an adsorption–desorption
equilibrium. Then, the mixture was irradiated for 10 min, and 2 mL
of the suspension was taken, followed by centrifugation to remove
the solid. The concentration of centrifuged solution was deter-
mined by UV–vis spectra based on the absorbance at 554 nm.
ꢀ
2
.4. Quantification experiments OH radicals
ꢀ
The amount of hydroxyl radicals ( OH radicals) generated in the
photocatalytic process can be determined by the terephthalic acid
ꢁ
4
ꢁ3
(
TA) fluorescence method, as TA (5 ꢃ10 M in a 2 ꢃ10 M NaOH
Fig. 3. UV–vis diffuse reflectance spectra of SrBiO Cl and BaBiO Cl.
2
2

2
08
H. Huang et al. / Materials Research Bulletin 62 (2015) 206–211
(
2
ICSD #84636) and BaBiO Cl (ICSD #79532), and no other peaks
were found, indicating the high purity and crystallinity of the
samples.
The microstructures and surface morphology of SrBiO
BaBiO Cl were investigated by a scanning electron microscope
SEM). The SEM images (Fig. S1) revealed that the products of
SrBiO Cl and BaBiO Cl all consist of layer-stacking structures
2
Cl and
2
(
2
2
formed by nanoplates. The results confirmed their layered crystal
configuration.
3
.2. Optical properties
2 2
The optical properties of SrBiO Cl and BaBiO Cl were studied by
UV–vis diffuse reflectance spectra (DRS). From Fig. 3, it can be seen
that they all possess strong light absorption in the UV region, and
2 2
SrBiO Cl can absorb more UV light than BaBiO Cl. Their band gaps
can also be determined by the DRS. In semiconductors, the square
of absorption coefficient is linear with energy for direct optical
transitions in the absorption edge region; whereas the square root
of absorption coefficient is linear with energy for indirect
2 2
Fig. 4. Band gaps of SrBiO Cl and BaBiO Cl.
3
. Results and discussion
.1. Characterization on structure of photocatalyst
SrBiO Cl and BaBiO Cl possess the similar crystal structures
3
2 2
transitions [20]. The absorption edges of SrBiO Cl and BaBiO Cl
2
are caused by direct transition. Data plots of absorption versus
energy in the absorption edge region are shown in Fig. 4. Band gaps
2
2
with the same orthorhombic space group Cmcm. As displayed in
Fig. 1a–c, their unique layered crystal structures are constructed by
2 2
of SrBiO Cl and BaBiO Cl are determined by optical absorption
near the band edge by the equation:
+
ꢁ
the alternatively arranged (Sr/BaBiO
along b axis. The neighboring (Sr/BaBiO
2
)
layers and Cl ion layers
n=2
+
a
hn
¼ Aðh
n
ꢁ E
g
Þ
(1)
2
) layers oppositely stack
ꢁ
to form large enough caves to allow the location of Cl ions. The
crystallization phases of the title compounds were characterized
by X-ray diffraction (XRD). Fig. 2a and b presents the XRD patterns
where ,h
a
n
, A and E
g
are optical absorption coefficient, the
photonic energy, proportionality constant, and band gap, respec-
tively [15]. By extrapolating the straight line to the x-axis in this
of SrBiO
2
Cl and BaBiO
2
Cl, respectively. It can be seen that all the
Cl
plot, the E
g 2 2
of SrBiO Cl and BaBiO Cl were estimated to be 3.52 and
diffraction peaks can be indexed into the orthorhombic SrBiO
2
3.71 eV, respectively. Furthermore, we can calculate their
Fig. 5. (a) Photocatalytic degradation curves of RhB over SrBiO
spectral patterns of RhB over (c) SrBiO Cl and (d) BaBiO Cl.
2 2
Cl and BaBiO Cl under UV light irradiation. (b) Kinetic fit for the degradation of RhB. Temporal absorption
2
2

H. Huang et al. / Materials Research Bulletin 62 (2015) 206–211
209
2 2
Fig. 6. Cycling runs in the photocatalytic degradation of RhB in the presence of (a) SrBiO Cl and (b) BaBiO Cl under UV light irradiation. Comparison of XRD patterns of (c)
SrBiO Cl and (d) BaBiO Cl before and after photoreaction.
2
2
conduction and valence band positions through the following Eqs.
2) and (3):
2
the characteristic band of RhB over BaBiO Cl (Fig. 5d) still
remained after 60 min irradiation. To quantitatively compare the
(
photocatalytic efficiency, the first order kinetics curves are plotted
E
VB ¼ X ꢁ E
e
þ 0:5E
g
(2)
ꢁ1
in Fig. 5b. The apparent rate constant kapp is 0.056 min
and
ꢁ1
0
.037 min
photocatalytic efficiency of SrBiO
than that of BaBiO Cl. Moreover, the cycling performance and
for SrBiO
2
Cl and BaBiO
2
Cl, respectively. Thus, the
2
Cl is about 1.51 times higher
E
CB ¼ EVB ꢁ E
g
(3)
2
where X is the electronegativity of the semiconductor (geometric
average of the absolute electronegativity of the constituent atoms),
E
e
is the energy of free electrons on the hydrogen scale (E
eV), ECB is the CB potential, and EVB is the VB potential. The ECB and
VB of SrBiO
e
ꢄ 4.5
E
2
Cl were estimated to be ꢁ0.9 and 2.62 eV, and the ECB
and EVB of BaBiO
respectively.
2
Cl were calculated to be ꢁ0.8 and 2.91 eV,
3.3. Photocatalytic activity
The photocatalytic activities of SrBiO
2 2
Cl and BaBiO Cl samples
were evaluated by photodecomposition of the organic dyes
rhodamine B (RhB) under UV light irradiation. There is almost
no photolysis of RhB without the presence of photocatalyst,
indicating that RhB was stable under UV light. As shown in Fig. 5a,
SrBiO
and 99% RhB can be photodecomposed by SrBiO
absorption spectra depicted in Fig. 5c revealed that the main
absorption peak of RhB molecules at 554 nm catalyzed by SrBiO Cl
disappeared after 45 min under UV light irradiation. Nevertheless,
2
Cl exhibits a higher photocatalytic activity than BaBiO
2
Cl,
2
Cl in 60 min. The
2
2 2
Fig. 7. Photoluminescence (PL) emission spectra of SrBiO Cl and BaBiO Cl.

210
H. Huang et al. / Materials Research Bulletin 62 (2015) 206–211
2 2
Scheme 1. Photocatalytic mechanism scheme of SrBiO Cl or BaBiO Cl under UV light irradiation.
2 2
Fig. 8. Fluorescence emission spectra of TAOH solutions generated by (a) SrBiO Cl and (b) BaBiO Cl.
stability of the two photocatalysts was evaluated by reclaiming and
re-examining the used samples for two extra cycles. As revealed in
BaBiO
2
Cl possess much more positive potentials (2.62 eV and
2.91 eV for SrBiO
2
Cl and BaBiO
2
Cl, respectively) than that of
ꢁ
ꢀ
ꢁ
Fig. 6a and b, the photocatalytic activity of SrBiO
2
Cl and BaBiO
2
Cl
OH / OH (+1.99 eV vs NHE). Thus, they could oxidize OH to
ꢀ
did not exhibit any loss for the photodegradation of RhB under UV
light irradiation. The XRD analyses were also performed on the
used SrBiO Cl and BaBiO Cl photocatalysts after photoreaction. As
2 2
shown in Fig. 6c and d, there is no change in the XRD patterns of the
two photocatalysts after photoreaction. The results indicated that
generate abundant active OH radicals, which are the active species
with powerful oxidization ability for efficient decomposition of
RhB [24,25]. In order to confirm the supposed photocatalytic
mechanism, terephthalic acid photoluminescence probing tech-
nique (TA-PL) was used to detect the generated OH radicals,
because TA can react with OH radicals to produce a highly
fluorescent 2-hydroxyterephthalic acid (TAOH). As shown in Fig. 8a
and b, the fluorescence emission intensities generated by the two
photocatalysts all obviously increased as prolonging the irradiation
ꢀ
ꢀ
SrBiO
the photocatalytic process. These results demonstrated that
SrBiO Cl and BaBiO Cl display good cycling performance and high
stability.
2
Cl and BaBiO
2
Cl are stable and not photo corroded during
2
2
ꢀ
time, demonstrating that the OH radicals serve as active species
3.4. Photocatalytic mechanism
and play important roles in degradation of RhB. Furthermore, the
emission intensity observed over SrBiO
that over BaBiO
generated by SrBiO
performance. It may be due to the more UV light absorption of
SrBiO Cl.
2
Cl is obviously higher than
Cl, which indicated that more OH radicals were
ꢀ
Photoluminescence (PL) emission spectra can be utilized to
2
survey the separation efficiency of the photogenerated charge
carriers of a semiconductor, as PL spectra mainly result from the
recombination of free carriers [21–23]. The lower PL intensity
indicates the slower recombination rate of charge carriers, and the
higher photocatalytic activity. Fig. 7 presents the PL spectra of
2
Cl, accounting for its better photocatalytic
2
4. Conclusion
2
SrBiO Cl and BaBiO Cl as two novel layered photocatalysts were
2 2 2
SrBiO Cl and BaBiO Cl. It can be observed that SrBiO Cl displays a
lower emission peak, and thus possess the higher photocatalytic
activity, which is in consistent with the result from photodegrada-
tion experiment.
2
successfully developed by a solid-state reaction. The as-prepared
products consist of layer-stacking structures formed by nanoplates.
Scheme 1 illustrates the photocatalytic mechanism of SrBiO
2
Cl
2 2
The band gaps of SrBiO Cl and BaBiO Cl were determined to be
3.52 and 3.71 eV, respectively. The photodegradation experiment
demonstrated that RhB can be effectively photodegraded by the two
ꢁ
and BaBiO
2
Cl. Under UV light irradiation, the electrons (e ) can be
+
excited and transferred to the CB, and the holes (h ) remained in
the VB of the photocatalysts. Based on the above band level
2
photocatalysts under UV irradiation, and SrBiO Cl exhibits a higher
analysis, the photogenerated holes in the VB of SrBiO
2
Cl and
photocatalyticactivitythanBaBiO Cl. Itwas also confirmed by the PL
2

H. Huang et al. / Materials Research Bulletin 62 (2015) 206–211
211
ꢀ
spectra. TA-PL test indicated that OH radicals serving as active
[4] Z.G. Yi, J.H. Ye, N. Kikugawa, T. Kako, S.X. Ouyang, H. Stuart-Williams, H. Yang, J.
Y. Cao, W.J. Luo, Z.S. Li, Y. Liu, R.L. Withers, Nat. Mater. 9 (2010) 559.
[5] N.D. Feng, Q. Wang, A.M. Zheng, Z.F. Zhang, J. Fan, S.B. Liu, J.P. Amoureux, F.
Deng, J. Am. Chem. Soc. 135 (2013) 1607.
species play important roles in degradation of RhB. Moreover, the
amountof OHradicalsgeneratedoverSrBiO
ꢀ
2
Clishigherthanthatof
BaBiO
activity of SrBiO
2
Cl, which is in consistent with the higher photocatalytic
Cl.
[6] G. Wang, B.B. Huang, X.C. Ma, Z.Y. Wang, X.Y. Qin, X.Y. Zhang, Y. Dai, M. Hwan
Whangbo, Angew. Chem. Int. Ed. 52 (2013) 4810.
2
[
[
7] G. Liu, P. Niu, L.C. Yin, H.M. Cheng, J. Am. Chem. Soc. 134 (2012) 9070.
8] S.C. Zhang, C. Zhang, Y. Man, Y.F. Zhu, J. Solid State Chem. 179 (2006) 62.
Acknowledgments
[9] J. Bi, L. Wu, J. Li, Z. Li, X. Wang, X. Fu, Acta Mater. 55 (2007) 4699.
10] C.S. Pan, Y.F. Zhu, Environ. Sci. Technol. 44 (2010) 5570.
[
[
11] Y. Zheng, F. Duan, M. Chen, Y. Xie, J. Mol. Catal. A: Chem. 317 (2010) 34.
This work was supported by the National Natural Science
Foundation of China (Grant Nos. 51302251, 51172245), the
Fundamental Research Funds for the Central Universities
[12] X. Zhang, Z.H. Ai, F.L. Jia, L.Z. Zhang, J. Phys. Chem. C 112 (2008) 747.
[13] W. Wang, B. Huang, X. Ma, Z. Wang, X. Qin, X. Zhang, Y. Dai, M.-H. Whangbo,
Chem. Eur. J. 19 (2013) 14777.
[
[
[
14] L.Y. Xie, J.X. Wang, Y.H. Hu, S.Y. Zhu, Z.Y. Zheng, S.X. Weng, P. Liu, RSC Adv. 2
(
2652013052), and the special co-construction project of Beijing
(
2012) 9881.
city education committee, Key Project of Chinese Ministry of
Education (No.: 107023).
15] H.W. Huang, Y. He, Z.H. Lin, L. Kang, Y.H. Zhang, J. Phys. Chem. C 117 (2013)
22986–22994.
16] H.W. Huang, G. Chen, Y.H. Zhang, Inorg. Chem. Commun. 44 (2014) 46.
[
17] H.W. Huang, Y. He, X.X. Ran He, Jiang, Z.S. Lin, Y.H. Zhang, S.C. Wang, Inorg.
Appendix A. Supplementary data
Chem. Commun. 40 (2014) 215.
[18] H.W. Huang, G. Chen, S.B. Wang, L. Kang, Z.S. Lin, Y.H. Zhang, Mater. Res. Bull. 51
(
2014) 455.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.materres-
bull.2014.11.032.
[
[
19] L.Q. Ye, J.Y. Liu, Z. Jiang, T.Y. Peng, L. Zan, Appl. Catal. B 142 (2013) 1.
20] K.L. Zhang, C.M. Liu, F.Q. Huang, C. Zheng, W.D. Wang, Appl. Catal. B 68 (2006)
125.
[
21] H.W. Huang, S.B. Wang, N. Tian, Y.H. Zhang, RSC Adv. 4 (2014) 5561.
[
[
[
22] Y. Wang, X.C. Wang, M. Antonietti, Angew. Chem. Int. Ed. 50 (2011) 2–24.
23] J. Li, L.Z. Zhang, Y.J. Li, Y. Yu, Nanoscale 6 (2014) 167–171.
24] X.Y. Fan, L. Zang, M. Zhang, H.S. Qiu, Z. Wang, J. Yin, H.Z. Jia, S.L. Pan, C.Y. Wang,
Chem. Mater. 26 (2014) 3169–3174.
References
[
[
1] A. Kubacka, M. Fernández-García, G. Colón, Chem. Rev. 112 (2012) 1555.
2] H. Tong, S.X. Ouyang, Y.P. Bi, N. Umezawa, M. Oshikiri, J.H. Ye, Adv. Mater. 24
[25] H.W. Huang, Y. He, R. He, Z.S. Lin, Y.H. Zhang, S.C. Wang, Inorg. Chem. 53 (2014)
(
2012) 229.
8114–8119.
[
3] L. Shang, T. Bian, B. Zhang, D.H. Zhang, L.Z. Wu, C.H. Tung, Y.D. Yin, T.R. Zhang,
Angew. Chem. Int. Ed. 53 (2014) 250.