Chemoselective and highly efficient conversion of aromatic alcohols into aldehydes photo-catalyzed by Ag3PO4 in aqueous suspension under simulated sunlight

Article abstract of DOI:10.1016/j.catcom.2014.08.025

Achieving alcohol to aldehyde conversion in an energy efficient and environmentally benign way still remains a challenge. Here, we report chemoselective (> 99%) and efficient conversion (> 90%) of alcohols to corresponding aldehydes photocatalyzed by Ag

Full text of DOI:10.1016/j.catcom.2014.08.025

Catalysis Communications 58 (2015) 34–39
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Chemoselective and highly efficient conversion of aromatic alcohols into
aldehydes photo-catalyzed by Ag3PO4 in aqueous suspension under
simulated sunlight
b
b
M. Qamar a, , R.B. Elsayed , K.R. Alhooshani , M.I. Ahmed a,1, D.W. Bahnemann c
⁎
a
Center of Excellence in Nanotechnology (CENT), King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Department of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Institut fuer Technische Chemie, Leibniz Universität Hannover, Callinstrasse 3, D-30167 Hannover, Germany
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 June 2014
Received in revised form 17 August 2014
Accepted 20 August 2014
Available online 30 August 2014
Achieving alcohol to aldehyde conversion in an energy efficient and environmentally benign way still remains a
challenge. Here, we report chemoselective (N99%) and efficient conversion (N90%) of alcohols to corresponding
aldehydes photocatalyzed by Ag3PO4 in water at room temperature under simulated sunlight excitation. A plau-
sible mechanism for the observed high selectivity is proposed. The mechanism suggested that the reduction site
of the semiconductor photocatalysts is more critical to be engineered in order to obtain high chemoselectivity in
case of alcohol oxidation.
Keywords:
© 2014 Elsevier B.V. All rights reserved.
Silver orthophosphate (Ag3PO4)
Semiconductor photocatalysts
Heterogeneous catalysis
Alcohol oxidation
Sunlight
1. Introduction
On the contrary, semiconductor-mediated photocatalytic process in
context of selective oxidation is still in its infancy as new photocatalysts
Ever since the discovery of light-activated water splitting on a TiO2
electrode (the so-called Honda effect) [1], photocatalytic processes
have been widely investigated owing to their renewable attributes.
Most of the earlier studies involving photocatalysis focused on environ-
mental cleanup, H2 production, and CO2 reduction etc. [2–4]. Recently,
the utilization of the photocatalytic process for the synthesis of fine
chemicals via an environmentally benign pathway has been explored
[5–7]. Attempts have been made to achieve numerous functional
group transformations, such as amine to imine [8,9], nitro to azo [10],
aniline to azobenzene [11], hexane to hexanone and hexanol [12],
and alcohols to corresponding aldehydes, [13–17] among others. The
last one being one of the most important organic synthesis as aldehydes
are widely used in food, beverages, pharmaceutical industries and
as precursors in chemical industries [18,19]. In the conventional alcohol
oxidation approaches, many advances have been made where metal-
based selective and efficient oxidization reagents have evolved, but
the requirement of stoichiometric amounts of the metal oxidants and
accumulation of a considerable amount of waste is inevitable [18,20].
are being explored to achieve oxidation of alcohols in a green fashion.
Some of the photocatalysts investigated for alcohol oxidation include
CdS/graphene [21] and CdS/graphene/TiO2 [22]. Although selective
and complete oxidation of benzyl alcohol to benzaldehyde was achieved
in aqueous suspensions of Au/CeO2, the reaction rate was rather low
for the benzaldehyde formation (3.0 μmolh−1) [23,24]. Pristine (rutile
[13,15], anatase [17], and brookite [25]) as well as surface-modified tita-
nia (Nb2O5/TiO2 [26], Pt/TiO2 [27], transition metals/TiO2 [28]) were in-
vestigated and it was notably discerned that the rutile form was the
most selective oxidation photocatalyst [13]. Recently, chemoselective ox-
idation of alcohols was achieved using monolayer HNb3O8 2D nanosheets
under visible light irradiation [29]. In most of the previous studies, organ-
ic solvents were used to achieve high selectivity.
One of the intrinsic prerequisites of the photocatalysts for high selec-
tivity and conversion appears to be a combination of high oxidation po-
tential of valence band holes and low reduction potential of conduction
band electrons. Recently, silver orthophosphate (Ag3PO4) is reported to
have exceptional before-mentioned electronic attributes [30,31]. Here-
in, we report Ag3PO4-mediated selective, efficient and complete conver-
sion of some representative alcohols (benzyl alcohol (BA), 4-methoxy
benzyl alcohol (4-MBA) and cinnamyl alcohol (CA) to the correspond-
ing aldehydes with high yield in aqueous suspensions under simulated
sunlight excitation at room temperature.
⁎
Corresponding author. Tel.: +966 13860 7775; fax: +966 13860 7264.
E-mail addresses: qamar@kfupm.edu.sa (M. Qamar), bahnemann@iftc.uni-hannover.de
(D.W. Bahnemann).
1
Fax: +966 13 860 7264.
http://dx.doi.org/10.1016/j.catcom.2014.08.025
1566-7367/© 2014 Elsevier B.V. All rights reserved.

M. Qamar et al. / Catalysis Communications 58 (2015) 34–39
35
2. Experimental section
samples taken out at regular time interval was carried out by UPLC to
substantiate the GC-MS analysis. An exemplified time-dependent con-
version of benzyl alcohol to benzaldehyde is shown in Fig. 2. As can be
seen, ~90% of BA was converted to benzaldehyde with ~90% yield
after ~4 h of irradiation. A quantitative analysis of BA and benzaldehyde
concentrations revealed the mole-to-mole conversion. In order to assess
the performance and selectivity of Ag3PO4 for other alcohols, oxidation
of 4-MBA and cinnamyl alcohol was also studied. The results are sum-
marized in Table 1 and compared with some significant studies docu-
mented in the literature focusing on the selective photocatalytic
oxidation of alcohols. As was the case with BA, 4-MBA also underwent
N85% oxidation forming anisaldehyde with selectivity exceeding 99%
(on mole-to-mole conversion basis). However, in the case of cinnamyl
alcohol, although the conversion was ~90%, selectivity was partially
lost as benzaldehyde and benzene acetaldehyde were also formed in ad-
dition to cinnamaldehyde, whose yield was ~81%. Time-dependent con-
version of 4-methoxybenzyl alcohol into p-anisaldehyde and cinnamyl
alcohol into cinnamaldehyde is shown in Fig. 2(b) and (c), respectively.
Although one of the overriding limitations in achieving selective
oxidation by the photocatalytic process is the overoxidation of reactants
or products during longer irradiation time, no change in aldehyde con-
centration occurred even after 8 h signifying that the Ag3PO4 was
extremely selective for BA, but not for benzaldehyde oxidation. In a re-
cent study [32], the overoxidation or simultaneous oxidation of benzyl
alcohol and benzaldehyde has been attributed to the complexation of
benzaldehydes, unlike benzyl alcohol, with the TiO2 surface. Interesting-
ly, the overoxidation was much averted when the TiO2 surface was
substantially covered with the layers of WO3 as WO3 was found to be
passive towards surface complexation with benzaldehyde. In this
study, to investigate if there is any interaction between BA or benzalde-
hyde and Ag3PO4 surface, adsorption experiments were carried out by
Ag3PO4 was prepared following the synthesis procedure document-
ed in the literature.19a In a typical synthesis, a required amount of
Na2HPO4.7H2O (0.27 g, 0.001 mol) was dissolved in double distilled
water (50 ml) followed by addition of AgNO3 (0.34 g, 0.002 mol). A
bright yellow precipitate was immediately formed and the resulting sus-
pension was kept under stirring for 2 h for a complete reaction. The prod-
uct was collected by centrifugation, washed several times with water and
ethanol and was dried at 90 °C for overnight. Details of characterizations,
photocatalytic reactions, GC-MS analysis, photoluminescence studies and
in situ ATR-FTIR study have been provided in supplementary information.
3. Results and discussion
Fig. 1 shows scanning microscopic image and XRD pattern of Ag3PO4.
The particle agglomerates have sharp-faceted features of fractured sur-
faces and fall in the range of ~0.5 to 2 μm. The XRD analysis revealed the
formation of a single phase crystalline material and the peaks could be
indexed as those belonging to Ag3PO4 in the BCC structure (JCPDS no.:
6-505); the sharpness of the peaks is representative of a polycrystalline
material. Optical properties were examined by diffuse reflectance spec-
troscopy, Fig. 1(c) & (d), which evinced that Ag3PO4 is capable of ab-
sorbing light with wavelengths shorter than 530 nm. Direct and
indirect band gaps were measured to be 2.42 and 2.34 eV, respectively.
To evaluate the activity and selectivity of Ag3PO4, the oxidation reac-
tions were carried out in water at room temperature and ambient pres-
sure using a light source that simulated sunlight. The conversion of BA
to benzaldehyde was followed by GC-MS analysis and the complete
course of evolution in BA and benzaldehyde concentration with irradia-
tion time is presented in Fig. S2. In addition, analysis of irradiated
210
1600
(b)
1400
1200
1000
800
600
211
320
321
400
421
420
222
200
310
110
400
200
0
220
411
20
30
40
50
60
70
2 (deg.)
10.5
9.0
7.5
6.0
4.5
3.0
1.5
0.0
10
9
(c)
(d)
8
7
6
5
4
3
2
1
0
Eg = 2.42 eV
300 360 420 480 540 600 660 720 780 840
Wavelength (nm)
1.5
1.8
2.1
2.4
2.7
3.0
3.3
3.6
3.9
Photon energy (eV)
Fig. 1. (a) Field emission scanning electron microscopic image, (b) powder XRD patterns, and (c) & (d) diffuse reflectance of Ag3PO4.

36
M. Qamar et al. / Catalysis Communications 58 (2015) 34–39
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0.6
(b)
0.5
(a)
0.4
0.3
4-methoxybenzyl alcohol
4-methoxybenzaldehyde
Benzyl alcohol
Benzaldehyde
Benzyl alcohol without light or Ag3PO4
0.2
0.1
0.0
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
Irradiation time (h)
Irradiation time (h)
0.6
0.5
0.4
0.3
0.2
0.1
(c)
Cinnamyl alcohol
Cinnamaldehyde
0.0
0
1
2
3
4
5
6
7
8
Irradiation time (h)
Fig. 2. Change in the concentrations of (a) benzyl alcohol, (b) 4-methoxybenzyl alcohol and (c) cinnamyl alcohol into corresponding aldehydes upon irradiation. Experimental conditions:
Ag3PO4 = 2 gl−1, initial alcohol concentration = 0.6 mM, irradiation time = 8 h, and volume (H2O) = 130 ml.
stirring the aqueous suspension of Ag3PO4 with BA or aldehyde or mix-
ture of BA and benzaldehyde (1:1 volume ratio) under dark for 24 h.
After experiment, the catalyst was separated by centrifugation and
dried under vacuum, and the change in catalyst's surface was followed
by FTIR & Raman, while any change in alcohol or aldehyde concentra-
tion was analyzed by GC-MS. The presence of any trace of alcohol or
aldehyde was not noticeable, as could be seen from FTIR spectrums
illustrated in Fig. S3. Furthermore, GC-MS analysis did not indicate any
apparent change in alcohol or aldehyde concentrations. The dearth of
noticeable physisorption of BA or benzaldehyde onto the surface of
Ag3PO4 explains, to a certain extent, the suppression of aldehyde oxida-
tion. Furthermore, controlled experiments, in the absence of catalyst or
Table 1
A comparative oxidation of selected aromatic alcohols by heterogeneous photocatalytic process.
Catalyst
Substrate
Product
Conversion
(%)
Selectivity
(%)
Yield
(%)
Conditions
Reference
TiO2
BA
4-MBA
BA
BA
BA
4-MBA
BA
BA
BA
4-MBA
BA
4-MBA
Cinnamyl alcohol
BA
BA
4-MBA
Benzaldehyde
p-Anisaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
p-Anisaldehyde
Benzaldehyde
Benzaldehyde
Benzaldehyde
p-Anisaldehyde
Benzaldehyde
p-Anisaldehyde
Cinnamaldehyde
Benzaldehyde
Benzaldehyde
p-Anisaldehyde
Benzaldehyde
Benzaldehyde
p-Anisaldehyde
Cinnamaldehyde
50
50
42
46
90
65
45
N80
N99
50
87
85
95
~9
20
63
50
38
60
95
95
95
(*)
90
N90
N99
56
68
90
71
92
N99
85
56
(*)
(*)
(*)
(*)
(*)
41.5
45
b80
N99
(*)
(*)
(*)
(*)
(*)
(*)
(*)
(*)
H2O, UV light
[13,14]
[16]
TiO2
SiO2/TiO2
SiO2/TiO2 (modified with H2SO4)
TiO2
CdS/graphene
CdS/graphene/TiO2
Au/CeO2
TiO2
Pt/TiO2
Trifluorotoluene, UV light
H2O, UV light
[17]
[21]
[22]
[23,24]
[25]
Trifluorotoluene, visible light
Trifluorotoluene, visible light
H2O, visible light
H2O, UV light
H2O, visible light
[27]
Ir/TiO2
HNb3O8
H2O, UV light
Benzotrifluoride, visible light
[28]
[29]
WO3/TiO2
Ag3PO4
BA
BA
H2O, light N350 nm
H2O, simulated sunlight
[32]
[in this study]
N85
N85
~90
N99
N99
N90(**)
~85
~85
~81
4-MBA
Cinnamyl alcohol
(*) not mentioned, (**) traces of benzaldehyde and benzene acetaldehyde were also formed. BA—benzyl alcohol; 4-MBA—4-methoxy benzyl alcohol.

M. Qamar et al. / Catalysis Communications 58 (2015) 34–39
37
1004
1314
1206
1697
826
1599
1012
1585
(a)
Reference-benzaldehyde/water
(b)
1655
1393
1456
924
1023
0.1
0.1
dark-120 min
dark-105 min
dark-90 min
light-120 min
dark-80 min
dark-70 min
light-105 min
light-90 min
light-80 min
light-70 min
light-60 min
dark-60 min
dark-50 min
dark-40 min
dark-30 min
light-50 min
light-40 min
light-30 min
light-20 min
light-10 min
light-0 min
dark-20 min
dark-10 min
dark-0 min
Reference-benzylalcohol/water
1000 1250 1500 1750 2000 2250 2500 2750
Wavenumber (cm-1)
1000 1250 1500 1750 2000 2250 2500 2750
Wavenumber (cm-1)
Fig. 3. Change in selected ATR-FTIR spectra of BA with time in the presence of Ag3PO4 (a) under light and (b) under dark.
light, were also performed which did not show any change in alcohol
concentration, indicating that both light and catalyst were required to
trigger and sustain the oxidation.
Absorption bands of BA modified gradually with respect to irradiation
time and started to resemble that of benzaldehyde. Notably, the absorp-
tion band corresponding to the carbonyl (C_O) stretching vibration,
which essentially differentiate BA and benzaldehyde, apparently
appeared at ~1697 cm−1. This band appeared after 20 min of irradiation
and the intensity was steadily increased with irradiation time. Whereas
under dark, with or without Ag3PO4, it did not appear even after
120 min of irradiation corroborating our earlier observation that light
and Ag3PO4 were necessary to instigate the oxidation of BA.
Unlike previous reports on the photocatalytic oxidation of alcohols
as presented in Table 1, greater selectivity was observed in this study.
Essentially, the non-selective nature of photocatalysis could be attribut-
ed to the formation of extremely reactive and short-lived radicals such
as OH•, O2−•, HO2• etc. O2 is readily reduced to O−2 • by excited conduction
The course of BA oxidation was also pursued by an in situ ATR-FTIR
analysis and this study was carried out in conditions analogous to
photocatalytic conditions. A time-dependent evolution in ATR-FTIR
spectra in the presence of Ag3PO4 under light and darkness is presented
in Fig. 3. The spectrums of BA and benzaldehyde solution prepared
in water were also recorded and included in Fig. 3 for comparison.
Aldehyde C\H stretches at ~2700 and 2800 cm−1 were not observed.
Under the light, the intensity of absorption bands at 1655 cm−1 was de-
creased while the intensity of bands at 924, 1004, 1023, 1206, 1393 and
1456 cm−1 was found to increase with increasing irradiation time. Few
new absorption bands appeared at 826, 1012, 1585 and 1599 cm−1
.
H
H
C
O
H
e
e
H
H
H
C
C
O
H
O
H
H
H
H
e
[O]
H
H
H
C
h
C
O
O
H
e
e
H
C
H
H
C
O
O
H
O
H
H
H
Scheme 1. A probable mechanism of photocatalytic oxidation of BA.

38
M. Qamar et al. / Catalysis Communications 58 (2015) 34–39
111
–
O2•
* Ag
*
O2
200
311
X
220
*
*
*
Ag**
–
– –
–
–
–
8 h
6 h
4 h
2 h
1 h
0 h
+ + + + +
H+ + OH•
20
30
40
50
60
70
80
2 (deg.)
H2O
Fig. 4. XRD patterns of Ag3PO4 collected after different irradiation time showing the forma-
tion of metallic Ag. Ag**–metallic Ag collected after dissolving the mixture of Ag and
Ag3PO4 obtained after irradiation experiments.
Scheme 2. Schematic showing involvement of O−2 •, OH• and holes in the selective photo-
catalytic oxidation of alcohols. R = aryl group.
band electrons while the holes in the valence band can oxidize water,
generating OH• radicals. These radical species are extremely reactive,
though short lived, and make the photocatalytic process somewhat
non-selective. Particularly, O2 may affect the overall photocatalytic oxi-
dation in two ways; as an oxidant (electron acceptor) or direct incorpo-
ration of molecular oxygen to yield a product. Hence, formation or the
involvement of such radicals was examined in order to understand
the operative mechanism responsible for the high selectivity. To deter-
mine the role of O−2 •, the oxidation of BA was carried out both in the ab-
sence and presence of molecular O2, by bubbling N2 or O2 through
photoreactor. Results showed that the conversion was independent of
the ambient environment, indicating that O2 seemingly did not play
any role in the oxidation of BA. This could be attributed to the lower
or more negative redox potential of O2/O2 − • (−0.16 eV, 1 M vs. NHE
at pH = 7 [33,34]) than the electrode potential of Ag3PO4 (+0.8 eV
vs. NHE at pH = 7) [30]. The findings further suggested that the oxida-
tion of alcohols via the photocatalytic process essentially proceeds
through the involvement of valence band holes, rather than direct
incorporation of molecular oxygen. Based on these observations, a plau-
sible mechanism involving 2 electrons and protons transfer process that
operates in the oxidation of alcohols to corresponding aldehydes is illus-
trated in Scheme 1. Furthermore, the path A appears to be more likely as
the formation of radical at the β-carbon may result in the delocalization
of this electron in the adjacent benzene ring, imparting additional
stability and rather thermodynamically favorable oxidation of BA. It
seemed plausible to postulate that the excited electrons were taken
up by Ag+ ions of the Ag3PO4 because the standard redox potential of
Ag (I) (Ag+/Ag0 = +0.8 eV) is higher or more positive than the conduc-
tion band potential of Ag3PO4 which implies that the Ag+ is likely to be
reduced to Ag0 by excited conduction band electrons. This assumption
was corroborated by XRD analysis of irradiated/used Ag3PO4, which
showed the presence of metallic silver in the sample. Change in the
structure of Ag3PO4 or appearance of metallic silver with respect to
irradiation time was followed by XRD and obtained diffraction patterns
are presented in Fig. 4. In addition to characteristic diffraction peaks
of Ag3PO4 which indicated the retention of basic Ag3PO4 structure,
4 new peaks (indicated with “*”) appeared which can be indexed
as the (111), (200), (220) and (311) planes of metallic silver (JCPDS
No. 04-0783). Moreover, formation of metallic silver with respect to ir-
radiation time was also analyzed quantitatively by gravimetric analysis
and the obtained values are listed in Table S1. As could be seen, the
amount of Ag0 increases with the increase in irradiation time. For com-
parison, typical XRD diffraction patterns of Ag collected after irradiation
reaction have been presented in Fig. 4. The patterns confirmed that the
collected Ag was metallic and pure (free from silver phosphate).
Additionally, the role of OH• produced through water oxidation
in the reaction media was investigated. Since terephthalic acid
tends to trap OH• radicals and gets transformed into fluorescent 2-
hydroxyterephthalic [35], photocatalytic experiments were performed
to monitor the generation of OH• via employing terephthalic acid as a
probe molecule both in the absence or presence of BA. The change
in fluorescence intensity, which is a function of OH radicals, was moni-
tored by photoluminescence. The time-dependent evolution of the
600
600
10 min
8 min
(a)
(b)
500
500
400
400
300
6 min
300
10 min
4 min
200
200
2 min
0 min
100
100
0 min
0
0
380
400
420
440
460
480
500
380
400
420
440
460
480
500
Wavelength (nm)
Wavelength (nm)
Fig. 5. Change in fluorescence intensity of terephthalic acid with respect to irradiation time in aqueous suspensions of Ag3PO4 in (a) the absence or (b) the presence of BA.

M. Qamar et al. / Catalysis Communications 58 (2015) 34–39
39
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Acknowledgements
Cycle 0
Cycle 1st
The authors acknowledge the support provided by King Abdulaziz
City for Science and Technology (KACST) through the Science & Tech-
nology Unit at King Fahd University of Petroleum & Minerals (KFUPM)
for funding this work through project no. 10-NAN1387-04 as part of
the National Science, Technology and Innovation Plan. The support of
the Center of Excellence in Nanotechnology and Department of Chemis-
try, KFUPM is gratefully acknowledged.
Cycle 2nd
Cycle 3rd
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.catcom.2014.08.025. These data include MOL files
and InChiKeys of the most important compounds described in this
article.
0
1
2
3
4
5
Irradiation time (h)
Fig. 6. Effect of Ag3PO4 recycling on the formation of benzaldehyde from benzyl alcohol.
Experimental conditions: Ag3PO4 = 2 gl−1, initial alcohol concentration = 0.6 mM, irradi-
ation time = 4 h, and volume (H2O) = 130 ml.
References
fluorescence spectra for terephthalic or 2-hydroxyterephthalic acid in
the absence or presence of BA is shown in Fig. 5. High intensity was ob-
served when terephthalic acid was irradiated without BA, indicating
generation of OH• via oxidation of H2O. However, in the presence of
BA, the intensity was strongly suppressed revealing preferred oxidation
of BA over that of water. The observed role of O2, accompanied by Ag+
to Ag0 reduction and suppression of OH• formation, corroborates the
plausible mechanism depicted in Scheme 2 for the selective oxidation
of alcohols in the presence of Ag3PO4.
The recyclability of Ag3PO4 was investigated under the identical
experimental conditions as applied for the study of photocatalytic oxi-
dation of BA. After the completion of the reaction (each cycle), the cat-
alyst was collected by centrifugation, washed with water and ethanol,
dried at 90 °C and was utilized for the next cycle. The effect of recycla-
bility on the formation of benzaldehyde is shown in Fig. 6. As could be
seen, the benzaldehyde formation was decreased by ~12%, 28% and
48% for the cycles first, second and third, respectively. The decrease
in the photocatalytic efficiency of Ag3PO4 may be explained in terms
of silver reduction (Ag+1–Ag0) by the excited electrons during photo-
catalytic processes, as discussed above and presented in Scheme 2. As
the irradiation/exposure time of Ag3PO4 increases, more and more silver
are likely to undergo photoreduction and thus leading to the decrease in
the photocatalytic efficiency of the catalyst after every cycle.
[1] A. Fujishima, K. Honda, Nature 238 (1972) 37.
[2] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann, Chem. Rev. 95 (1995) 69.
[3] K. Maeda, K. Teramura, D. Lu, T. Takata, N. Saito, Y. Inoue, K. Domen, Nature 440
(2006) 295.
[4] O.K. Varghese, M. Paulose, T.J. LaTempa, C.A. Grimes, Nano Lett. 9 (2009) 731.
[5] T.P. Yoon, M.A. Ischay, J. Du, Nat. Chem. 2 (2010) 527.
[6] G. Palmisano, V. Augugliaro, M. Pagliaro, L. Palmisano, Chem. Commun. (2007)
3425.
[7] X. Lang, X. Chen, J. Zhao, Chem. Soc. Rev. 43 (2014) 473.
[8] X.J. Lang, H.W. Ji, C.C. Chen, W.H. Ma, J.C. Zhao, Angew. Chem. Int. Ed. 50 (2011)
3934.
[9] F.Z. Su, S.C. Mathew, L. Mohlmann, M. Antonietti, X.C. Wang, S. Blechert, Angew.
Chem. Int. Ed. 50 (2011) 657.
[10] H. Zhu, X. Ke, X. Yang, S. Sarina, H. Liu, Angew. Chem. Int. Ed. 49 (2010) 9657.
[11] S. Li, U. Diebold, J. Am. Chem. Soc. 132 (2010) 64.
[12] Y. Ide, N. Kawamoto, Y. Bando, H. Hattori, M. Sadakane, T. Sano, Chem. Commun. 49
(2013) 3652.
[13] D. Yurdakal, G. Palmisano, V. Loddo, V. Augugliaro, L. Palmisano, J. Am. Chem. Soc.
130 (2008) 1568.
[14] G. Palmisano, E. Garcia-Lopez, G. Marci, V. Loddo, S. Yurdakal, V. Augugliaro, L.
Palmisano, Chem. Commun. 46 (2010) 7074.
[15] V. Augugliaro, T. Caronna, V. Loddo, G. Marc, G. Palmisano, L. Palmisano, S. Yurdakal,
Chem. Eur. J. 14 (2008) 4640.
[16] Q. Wang, M. Zhang, C. Chen, W. Ma, J. Zhao, Angew. Chem. Int. Ed. 49 (2010) 7976.
[17] G. Palmisano, S. Yurdakal, V. Augugliaro, V. Loddo, L. Palmisano, Adv. Synth. Catal.
349 (2007) 964.
[18] H. Miyamura, R. Matsubara, Y. Miyazaki, S. Kobayashi, Angew. Chem. 119 (2007)
4229.
[19] M. Hundlucky, Oxidations in Organic Chemistry, American Chemical Society,
Washington, DC, 1990. 114–163.
[20] Y. Uozumi, R. Nakao, Angew. Chem. Int. Ed. 42 (2003) 194.
[21] N. Zhang, Y. Zhang, X. Pan, X. Fu, S. Liu, Y.-J. Xu, J. Phys. Chem. C 115 (2011) 23501.
[22] N. Zhang, Y. Zhang, X. Pan, M.-Q. Yang, Y.-J. Xu, J. Phys. Chem. C 116 (2012) 18023.
[23] A. Tanaka, K. Hashimoto, H. Kominami, Chem. Commun. 47 (2011) 10446.
[24] A. Tanaka, K. Hashimoto, H. Kominami, J. Am. Chem. Soc. 134 (2012) 14526.
[25] M. Addamo, V. Augugliaro, M. Bellardita, A.D. Paola, V. Loddo, G. Palmisano, L.
Palmisano, S. Yurdakal, Catal. Lett. 126 (2008) 58.
[26] S. Furukawa, T. Shishido, K. Teramura, T. Tanaka, ACS Catal. 2 (2012) 175.
[27] W. Zhai, S. Xue, A. Zhu, Y. Luo, Y. Tian, ChemCatChem 3 (2011) 127.
[28] W. Feng, G. Wu, L. Li, N. Guan, Green Chem. 13 (2011) 3265.
[29] S. Liang, L. Wen, S. Lin, J. Bi, P. Feng, X. Fu, L. Wu, Angew. Chem. Int. Ed. 53 (2014) 1.
[30] Z. Yi, J. Ye, N. Kikugawa, T. Kako, S. Ouyang, H. Stuart-Williams, H. Yang, J. Cao, W.
Luo, Z. Li, Y. Liu, R.L. Withers, Nat. Mater. 9 (2010) 559.
[31] Y. Bi, S. Ouyang, N. Umezawa, J. Cao, J. Ye, J. Am. Chem. Soc. 133 (2011) 6490.
[32] D. Tsukamoto, M. Ikeda, Y. Shiraishi, T. Hara, N. Ichikuni, S. Tanaka, T. Hirai, Chem.
Eur. J. 17 (2011) 9816.
[33] D.T. Sawyer, J.S. Valentine, Acc. Chem. Res. 14 (1981) 393.
[34] M.D. Bartberger, W. Lie, E. Ford, K.M. Miranda, C. Switzer, J.M. Fukuto, P.J. Farmer, D.A.
Wink, K.N. Houk, PNAS 99 (2002) 10958.
4. Conclusions
We have demonstrated that selective and efficient photo-conversion
of alcohols into corresponding aldehydes with high yield could be
achieved with Ag3PO4 in water under mild conditions. Enhanced activ-
ity and selectivity are attributed to the high oxidation potential of
Ag3PO4, passive behavior of O−2 •, and weak generation and ineffective-
ness of OH• radicals. It seems likely that the valence band holes are the
primary catalytic sites for the oxidation of alcohols, rather than direct ox-
idation through molecular oxygen, and chemoselectivity hinges on the
engineering of reduction site or conduction band of the photocatalyst.
Mechanistic observations may be anticipated to offer impetus to identify
or custom-tailor other potential photocatalysts for selective photocatalyt-
ic oxidations. Although oxidation of few selected alcohols only was dem-
onstrated, Ag3PO4 is likely to be active for a variety of other essential
oxidation reactions.
[35] K. Ishibashi, A. Fujishima, T. Watanabe, K. Hashimoto, Electrochem. Commun. 2
(2000) 207.