Angewandte
Chemie
acetaldehyde, but also in the degradation of MB dye under
wide-ranging visible light irradiation. Furthermore, its activity
and crystal structure did not change after a series of
continuous investigations under different experimental con-
ditions. Furthermore, this work provides some insight into the
design of new green heterogeneous photocatalysts for the
degradation of organic contaminants.
Experimental Section
The CaBi O photocatalyst was prepared by a simple soft chemical
2
4
method. Stoichiometric amounts of Ca(NO ) ·4H Oand
3
2
2
Bi(NO ) ·5H Owere dissolved in water. The composite was formed
3
3
2
by adding a solution of ethylenediaminetetraacetic acid in ammonia
and citric acid to the above aqueous solution. A xerogel was then
prepared by ageing and drying the composite. The xerogel was
calcined at 623 K for 10 h, and crystallized at 1073 K for 12 h in air.
The crystal structure of the sample was determined by X-ray
diffraction methods (JEOL JDX-3500 Tokyo, Japan). The UV/Vis
diffuse reflectance spectrum of CaBi O was measured on a UV/Vis
Figure 4. Pictures of solutions of MB: a) before photocatalytic
degradation; b) after photocatalytic reaction (120 min) over CaBi O ;
c) after photocatalytic reaction (120 min) over TiO2.
2
4
2
4
[
14]
spectrometer (UV-2500, Shimadzu). The surface area of the material
was measured by BET measurements of nitrogen adsorption at 77 K
center, respectively. For bismuth(iii)-based semiconductors,
it was also found that the Bi 6s and O2p levels can form a
preferable hybridized VB. In terms of the above depiction,
(
Micromeritics Automatic Surface Area Analyzer Gemini 2360,
[
15]
2
À1
Shimadzu). TiO (surface area 50 m g ) is commercially available
2
we assumed that the VB of CaBi O4 is composed of
and was used as a reference photocatalyst. The photocatalytic
decompositions of acetaldehyde was performed with 1.0 g of the
powdered photocatalyst placed at the bottom of a Pyrex glass cell at
room temperature in a gas-closed system; the reaction gas mixture
2
hybridized Bi 6s and O2p orbitals, whereas the CB is
composed of Bi 6p orbitals, and these bands meet the
potential requirements of organic oxidation. An active
photocatalyst for the decomposition of the organic com-
pounds must have a VB with strong oxidizing ability and
photogenerated holes with high mobility. The hybridized VB
of CaBi O has shown strong oxidative ability in the work
(
0.5 atm) consisted of 837 ppm CH CHO, 21% O , and Ar balance
3
2
gas. The photocatalytic degradation of MB was carried out with 0.3 g
of the powdered photocatalyst suspended in a solution of MB
À1
(
15.3 mgL , 100 mL), which was prepared by dissolving the MB
2
4
powder in distilled water in a Pyrex glass cell at room temperature
under air. The optical system for the catalytic reaction included a
described herein. Meanwhile, the hybridization of the Bi 6s
and O2p levels makes the VB largely dispersed, which favors
300 W Xe arc lamp (focused through a shutter window), a cutoff filter
[
16]
(providing visible light of different wavelengths), and a water filter (to
the mobility of photoholes in the VB and is beneficial to the
oxidation reaction.
prevent IR irradiation). CO and acetaldehyde were detected by GC
2
(
CO , GC-8A with TCD detector, Shimadzu; acetaldehyde and other
2
The stability of a photocatalyst is important to its
organic substances, GC-14B with FID detector, Shimadzu). MB
degradation was determined by UV/Vis spectroscopy (UV-2500,
Shimadzu).
application; doped TiO photocatalysts sometimes suffer
2
[
2]
from this problem. After each photocatalytic degradation
reaction of organic contaminants, the crystal structure of the
Received: December 22, 2003
Revised: May 11, 2004 [Z53594]
CaBi O4 photocatalyst was checked by X-ray diffraction
2
(
XRD) analysis. The analysis showed that CaBi O belongs to
2 4
a monoclinic crystal structure (space group: I2/a, a = 1.4002,
[
17]
Keywords: dyes/pigments · green chemistry · heterogeneous
catalysis · photochemistry · photooxidation
b = 1.1596, c = 1.2198 nm, b = 101.5418). XRD analysis of
the sample also showed that the crystal structure of the
photocatalyst was not changed after the photocatalytic
reaction. The stability of the photocatalyst will be investigated
further in more detail by other characterization methods. The
BET (Brunauer–Emmett–Teller) measurement showed that
the surface area of the CaBi O photocatalyst was only
.
[1] For relevant reviews, see: a) A. Mills, R. H. Davies, D. Worsley,
Chem. Soc. Rev. 1993, 22, 417; b) M. R. Hoffman, S. T. Martin,
W. Choi, D. W. Bahnemann, Chem. Rev. 1995, 95, 69; c) A. Mills,
S. L. Hunte, J. Photochem. Photobiol. A 1997, 108, 1; d) W. Choi,
A. Termin, M. R. Hoffman, J. Phys. Chem. 1994, 98, 13669; e) A.
Linsebigler, G. Lu, J. T. Yates, Chem. Rev. 1995, 95, 735.
2
4
2
À1
0
.6 m g , nearly 1% of the surface area of TiO . It is well
2
known that the surface area of a catalyst greatly affects its
[
18]
catalytic activity. The present method for the preparation of
the material greatly limits the activity of the photocatalyst.
Nano-sized photocatalysts are under investigation and are
expected to increase significantly the surface area of the
catalyst and therefore the photocatalytic activity.
[
2] R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, Y. Taga, Science
2001, 293, 269.
[3] a) X. Tao, W. Ma, T. Zhang, J. Zhao, Angew. Chem. 2001, 113,
103; Angew. Chem. Int. Ed. 2001, 40, 3014; b) W. Ma, J. Li, X.
Tao, J. He, Y. Xu, J. C. Yu, J. Zhao, Angew. Chem. 2003, 115,
059; Angew. Chem. Int. Ed. 2003, 42, 1029.
3
1
In summary, the CaBi O semiconductor was found to be
2
4
[
4] a) J. M. Herrmann, J. Disdier, P. Pichat, J. Catal. 1988, 113, 72;
b) D. S. Muggli, J. T. McCue, J. L. Falconer, J. Catal. 1998, 173,
a novel visible-light-driven photocatalyst for the degradation
of various organic contaminants. The catalyst exhibits a high
photocatalytic activity, not only in the decomposition of
470; c) X. Z. Li, F. B. Li, Environ. Sci. Technol. 2001, 35, 2381;
d) D. S. Muggli, L. Ding, M. J. Odland, Catal. Lett. 2002, 78, 23.
Angew. Chem. Int. Ed. 2004, 43, 4463 –4466
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