of electron–hole recombination, as displayed in Fig. 6.
2
Furthermore, the electronic acceptors like adsorbed O can
easily trap the electrons (transferred to the surface of SnO ) to
2
ꢁ
produce a superoxide anion radical ꢀO , which effectively
2
protects Ag PO semiconductors to avoid their photoreduction
3
4
+
ꢁ
ꢁ
(
Ag + e - Ag). Then the formed ꢀO may either attack
2
organic molecules or provide hydroxyl radical species (ꢀOH) by
23
reacting with hydrion and photogenerated electrons. On the
other hand, some of the photoinduced holes on the surface of
Ag PO
3
4
can be trapped (the quantity of the SnO
2
in the
PO
4
composites is small and the SnO
ꢁ
2
layer on the surface of Ag
3
is not a compact layer) by OH to further produce ꢀOH species,
which is an extremely strong oxidant for the partial or
2
4
complete mineralization of organic chemicals. Based on the
above aspects, it can be concluded that the proposed fabrica-
tion of Ag PO /SnO is a successful and general strategy to
3
4
2
develop highly active and stable photocatalysts under visible
light irradiation.
In conclusion, we have developed a facile approach for the
synthesis of Ag PO
3
4
/SnO
2
composite photocatalysts. Significantly,
PO particles, the Ag PO /SnO
compared with pure Ag
3
4
3
4
2
composite photocatalysts display enhanced photocatalytic
activity and good structural stability for MO degradation
under the irradiation of visible light. The insolubility of
SnO2 can effectively protect Ag PO from dissolution. The
Fig. 5 (a) XRD patterns of Ag
after 10 MO decomposition experiments. (b) The repeated bleaching
of MO over recycled Ag PO /SnO photocatalysts under visible light
l Z 420 nm).
3 4 3 4 2
PO and Ag PO /SnO photocatalysts
3
4
3
4
2
Ag PO /SnO composites improve the separation of photo-
3
4
2
(
generated electron–hole pairs, thus enhancing the photocatalytic
activity and avoid the photoreduction of Ag PO . It can be
3
4
protect the Ag PO4 from dissolution in aqueous solution,
3
3 4 2
expected that this kind of Ag PO /SnO composite may
thus the structural stability of Ag PO /SnO can be greatly
3
4
2
provide a new approach for high performance novel catalyst
design and fabrication towards new energy sources, green
chemistry, and environmental issues.
9
enhanced during the photocatalytic process. Secondly, as we
know, SnO has no absorption response to the visible light due
2
to its wide band gap, therefore, the light absorption of Ag
SnO composites was solely contributed by the Ag PO component
in the visible light photocatalysis experiments. However, the
Ag PO composites exhibited a more enhanced visible light
photocatalytic efficiency than pure Ag PO , which must be
correlated to the complex band configuration of the Ag PO
SnO photocatalysts. For Ag PO /SnO photocatalysts, the
conduction band and valence band potentials of SnO are
3 4
PO /
2
3
4
Acknowledgements
3
4
This work is supported by the National Basic Research
Program of China (973 Program) (No. 2012CB825800,
3
4
3
4
/
2
010CB934500), National Natural Science Foundation of
2
3
4
2
China (NSFC) (No. 51132006, 21073127, 21071104), A Foundation
for the Author of National Excellent Doctoral Dissertation of
P R China (FANEDD) (No. 200929), A Project Funded by the
Priority Academic Program Development of Jiangsu Higher
Education Institutions (PAPD) and a Project supported by the
Natural Science Foundation of the Jiangsu Higher Education
Institutions of China (Grant No. 11KJB150015).
2
7
,22
more positive than that of Ag PO .
3
Therefore, the photo-
4
generated electrons in the Ag PO can be easily transferred to
3
4
the surface of the SnO , and the photoinduced holes remain on
2
3 4
the surface of Ag PO , which promotes the effective separation of
photoexcited electron–hole pairs and decreases the probability
Notes and references
1
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0, 911.
Fig. 6 Schematic model for the important roles of SnO
2
for the high
photocatalytic activity and good stability in Ag PO /SnO .
2
3
4
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012
New J. Chem., 2012, 36, 1541–1544 1543