In situ liquid phase synthesis of hydrogen peroxide from molecular oxygen using gold nanoparticle-loaded titanium(IV) dioxide photocatalyst

Article abstract of DOI:10.1021/ja102651g

Gold nanoparticle loading has led to a drastic enhancement of TiO ₂-photocatalized generation of H₂O₂ from O ₂ with a unique inversed volcano-type relation between the activity and Au particle size.

Full text of DOI:10.1021/ja102651g

Published on Web 05/20/2010
In Situ Liquid Phase Synthesis of Hydrogen Peroxide from Molecular Oxygen
Using Gold Nanoparticle-Loaded Titanium(IV) Dioxide Photocatalyst
†
†
,†,‡
Miwako Teranishi, Shin-ichi Naya, and Hiroaki Tada*
EnVironmental Research Laboratory, Kinki UniVersity, 3-4-1, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan
and Department of Applied Chemistry, School of Science and Engineering, Kinki UniVersity, 3-4-1, Kowakae,
Higashi-Osaka, Osaka 577-8502, Japan
Received March 30, 2010; E-mail: h-tada@apch.kindai.ac.jp
H
2
O
2
has attracted much attention as a clean oxidant for organic
synthesis that emits only water as a byproduct with high atom
1
efficiency while being widely used in industry and households for
pulp bleaching, effluent treatment, disinfection, etc. At present, most
H O is produced by the anthraquinone method Via multisteps
2 2
2
requiring large amounts of energy and organic solvent. In addition,
concentrated H is explosive, and the careful treatment is
indispensable for its storage and transport. Direct synthesis of H
from H and O using Au and Pd nanoparticle (NP) catalysts has
2 2
O
2 2
O
2
2
3
recently been reported. Semiconductor photocatalysis mainly
studied for the purpose of environmental remediation is also
fascinating with its application as an “ideal green” synthesis. UV
4
Figure 1. (A) Plots of [H
Au/TiO with various size d or TiO
mass%) vs t . (B) Plots of [H ] at t
2
O
2
] under UV-irradiation in the presence of
or Pt/TiO (d ) 1.6 nm, x ) 0.19
) 6 h using Au/TiO vs d.
5
2
2
2
p
2
O
2
p
2
light irradiation to TiO
the usage of H gas. However, the concentration is only on a
micromolar order, and so far, the photocatalytic formation of H O
2
2 2 2 2
in water yields H O from O in situ without
2
under aerobic conditions. The H
2
O
concentration ([H
) was determined by iodometric
titration. Figure 1A shows time courses for the H generation
in the presence of various photocatalysts. Noticeably, Au/TiO
exhibits a high level of photocatalytic activity much greater than
those for TiO and Pt/TiO . The photonic efficiency (Φ, molecules
produced/incident photons) at the light wavelength (λ) ) 355 (
3 nm was calculated to be 13% by assuming a two-electron
reduction process. O , C OH, and UV light irradiation in addition
to the photocatalyst were necessary for this reaction to proceed
Figure S1 in Supporting Information (SI)). The Au NP loading
2 2
O ]) of the
2
2
filtrate at each irradiation time (t
p
6
has been studied from the mechanistic viewpoint. Such a low yield
of H is ascribable to its degradation Via the reduction of the
surface peroxide species resulting from the reaction of H with
the surface Ti-OH groups by the excited electrons. Recently, by
6
2 2
O
2 2
O
2
2 2
O
7
2
2
8
using a surface-fluorinated TiO
2
photocatalyst, the production of
2 2
H O
on a millimolar level has been achieved as a result of the
2
9
suppression of the degradation pathway. On the other hand, Au
particles smaller than 10 nm loaded on metal oxides are currently
being revealed to exhibit high catalytic activities for many important
2
2 5
H
(
1
0
chemical reactions including the electroreduction of O
2
,
low-
whereas
photocatalysis, the loading
of Au NPs is very effective in increasing its activity, for which the
photoinduced interfacial electron transfer (IET) from TiO to Au
2
was also effective for the TiO surface-fluorinated system, and Au/
11
12
temperature CO oxidation, and hydrogenation of C
the bulk Au is inactive. Also, in the TiO
2 2
H ,
-photocatalyzed reaction with NaF addition (0.1 mol dm-3)
TiO
2
2
2 2
afforded a 1 order larger amount of H O as compared to the value
previously reported (dotted curve in Figure 1A, Figure S2 in SI).
Another intriguing point is the d-dependence of the photocatalytic
9
2
is essentially responsible. This IET has the following two meanings:
one is the enhancement of the charge separation, and the other is
activity. Figure 1B shows the plots of [H
function of d. An inverse volcano-type curve with a minimum at d
3.5 nm is observed, whereas volcano-type profiles have been
2 2 p
O ] at t ) 6 h as a
the spatial separation of the oxidation sites (TiO
reduction sites (Au surface). On application of the TiO
talysis to synthesis, these are of great importance for achieving high
2
surface) and the
≈
2
photoca-
reported for the thermal catalysis of metal oxide-supported Au
11,12
NPs.
1
3
photocatalytic activity and high selectivity.
Herein we report a drastic enhancement of the TiO
lyzed generation of H from O by the Au NP loading to yield
on a 10 mM level and a unique activity-Au particle size
relation. To vary Au particle size (d) with its loading amount
maintained to be constant (x ) 0.25 mass%), Au/TiO was
synthesized by the deposition-precipitation (DP) method where
The decrease of the reaction rate with prolonging t
p
in Figure
2
-photocata-
1A suggests that the decomposition of H O occurs concurrently
2
2
2
O
2
2
with its formation. To evaluate the d-dependencies of the formation
and the decomposition, kinetic analysis was carried out. Under the
present conditions, by assuming that the formation and decomposi-
tion rates follow the zero-order and first-order kinetics toward
[H O ], respectively, one can obtain the following equation: [H O ]
2 2
H O
2
2
2
2
2
14
both heating temperature (T
photocatalyzed H synthesis was carried out as follows: Au/TiO
0.2 g) was added to H O (200 mL) containing 4% C
hole scavenger. After stirring the suspension in the dark for 1 h,
c
) and time (t
c
) were altered. Au/TiO
2
-
) (k /k ){ 1 - exp(-k t)}, where k is the formation rate constant
f
d
d
f
O
2 2
2
and k is the decomposition rate constant. As apparent from the
d
(
2
2
H
5
OH as a
calculated curves in Figure 1A, the experimental data were well
fitted with the equation, and Figure 2A shows the plots of k as a
f
-2
UV light (λ > 300 nm, I290-390 nm ) 3.0 mW cm ) was irradiated
function of d. The k values for Pt/TiO and Au/TiO are larger
f
2
2
2
than that for TiO , which can be attributed to the increase in the
†
charge separation efficiency due to the IET from TiO
NPs. It has recently been reported that the 2e reduction of O
2
to the metal
to
Environmental Research Laboratory.
Department of Applied Chemistry.
‡
-
2
7
850 9 J. AM. CHEM. SOC. 2010, 132, 7850–7851
10.1021/ja102651g  2010 American Chemical Society

C O M M U N I C A T I O N S
Scheme 1. Au/TiO
2
-Photocatalzyed H
2
O
2
Formation
f d d
Figure 2. (A) Plots of k vs d. (B) Plots of k and k -dark vs d.
formation (Figure 1B) is rationalized in terms of the d-dependences
of k and k (Scheme 1).
In summary, this study has shown that the liquid-phase Au/TiO
photocatalzyed H generation from O has a promising prospect
for in situ H synthesis. Recently, Au/TiO has also been found
to exhibit thermal catalytic activity for the chemoselective oxidation
generate H
2
O
2
preferentially proceeds on the Au surface, while the
-
15
f
d
4
e reduction to H
2
O occurs on the Pt surface. This explains the
for Au/TiO is much greater than that for Pt/TiO
Interestingly, all the k values of Au/TiO are smaller than half of
those of TiO and Pt/TiO (Figure 2B). This is probably because
the reduction of O takes place on the Au surface in the Au/TiO
system, while the TiO surface peroxides promote the H
degradation in the TiO
high catalytic activity for the H
remarkable accelerating effect of the Au NP loading on the TiO
photocatalyzed H synthesis is induced by both the enhancement
2
-
fact that the k
f
2
2
.
2
O
2
2
d
2
2
O
2
2
2
2
2
2
2
1
9
of alcohols to aldehydes in the presence of H
allow us to expect the development of an ideal catalytic organic
synthetic process consisting of the Au/TiO -photocatalyzed H
formation and the subsequent Au/TiO -catalyzed oxidation of
organic substances using the H as an oxidant.
2
O
2
.
These results
2
2
O
7
2
system. Also, Pt is well-known to have a
16
2
2 2
O
2
2
O decomposition. Evidently, the
2
2
-
2 2
O
2 2
O
of the formation and the restriction of the decomposition. Further,
the high efficiency of this reaction can be explained within the
framework of the idea of “reasonable delivery photocatalytic
Acknowledgment. Authors acknowledge the financial support
of a Grant-in-Aid for Scientific Research (B) No. 20350097 from
the Ministry of Education, Science, Sport, and Culture, Japan, and
Nippon Sheet Glass Foundation for Materials Science and
Engineering.
13
reaction systems”: (1) oxidation and reduction sites are separated
to TiO and Au NP, respectively, (2) sufficient amounts of O are
supplied to the reduction sites on the surface of Au NPs with high
2
2
17
Supporting Information Available: Experimental details; time
affinity to O
removal from the catalyst surface.
The unique d-dependence in this Au/TiO
formation is discussed on the presumption that both the formation
and decomposition of H mainly occurs at the reduction sites on
the Au surface. The Au surface area of Au/TiO decreases inversely
2 2 2 2
, (3) high solubility of H O to H O causes its smooth
courses for the H
2 2 f
O generation (Figures S1, 2); d-dependency of k ′
(
Figure S3). This material is available free of charge via the Internet at
2 2 2
-photocatalzyed H O
http://pubs.acs.org.
2
O
2
References
2
(
1) Sato, K.; Aoki, M.; Noyori, R. Science 1998, 281, 1646.
as d when x is constant (dotted line in Figure 2A). We have shown
by photoelectrochemical measurements and quantum chemical
(2) Reidl, H.; Pfleirender, G. U.S. Patent 2215883, 1940.
(
3) (a) Landon, P.; Collier, P. J.; Papworth, A. J.; Kiely, C. J.; Hutchings,
G. J. Chem. Commun. 2002, 2058. (b) Liu, Q.; Bauer, J. C.; Schaak, R. E.;
Lunsford, J. H. Angew. Chem., Int. Ed. 2008, 47, 6221.
calculations that the Fermi energy of Au NPs loaded on TiO
2
at
1
8
(4) Fujishima, A.; Zhang, X.; Tryk, D. A. Surf. Sci. Rep. 2008, 63, 515.
(
the photostationary state (E
TiO with the higher E
enhance the O reduction to increase k
F
′) rises as the d value increases. Au/
5) (a) Palmisano, G.; Augugliaro, V.; Pagliaro, M.; Palmisano, L. Chem.
Commun. 2007, 3425. (b) Hoffmann, N. Chem. ReV. 2008, 108, 1052.
6) (a) Cai, R.; Kubota, Y.; Fujishima, A. J. Catal. 2003, 219, 214. (b) Goto,
H.; Hanada, Y.; Ohno, T.; Matsumura, M. J. Catal. 2004, 225, 223. (c)
Hirakawa, T.; Nosaka, Y. J. Phys. Chem. C 2008, 112, 15818.
2
F
′ (i.e., the greater reducing power) would
(
2
f
, and actually, the k
f
′
normalized with respect to the Au surface area (k
f
) significantly
- d
curve deviates positively from the line proportional to d- to show
a gradual decrease in k with increasing d (Figure 2A). On the other
hand, plots of k vs d show a volcano-type curve with a maximum
at d ≈ 3.5 nm (k in Figure 2B). This profile well resembles that
for the H decomposition thermally catalyzed by Au/TiO in the
dark (k -dark in Figure 2B). The k -dark at the
same d value by a factor of ca. 2.5, which is also ascribable to an
increase in the reducing power with the photoinduced E upward
Further, the steep lowering in
′ at d < 5 nm is considered to cause the decrease in k at d <
.5 nm. Density functional theory calculations indicated that the
Au-TiO interfaces and/or low-coordinated Au atoms become
active sites in the Au/TiO
in k at d > 3.5 nm can be rooted in the diminution of the number
of such catalytic active sites on the Au NP surface. Consequently,
the k value is determined by the balance between the E ′ value
and the number of catalytic active sites on the Au NP surface, and
further, the activity-d relation in the Au/TiO -photocatalzyed H
(
7) Li, X.; Chen, C.; Zhao, J. Langmuir 2001, 17, 4118.
increasing with increasing d (Figure S3 in SI). As a result, the k
f
(
8) (a) Minero, C.; Mariella, G.; Maurino, V.; Pelizzetti, E. Langmuir 2000,
16, 2632. (b) Park, H.; Choi, W. J. Phys. Chem. B 2004, 108, 4086.
9) Maurino, V.; Minero, C.; Mariella, G.; Pelizzetti, E. Chem. Commun. 2005,
1
(
f
2
627.
d
(10) Inasaki, T.; Kobayashi, S. Electrochim. Acta 2009, 54, 4893.
(
11) Valden, M.; Lai, X.; Goodman, D. W. Science 1998, 281, 1647.
12) Jia, J.; Haruki, K.; Kondo, J. N.; Domen, K.; Tamaru, K. J. Phys. Chem.
B 2000, 104, 11153.
d
(
2
O
2
2
1
9
(
(
13) Tada, H.; Kiyonaga, T.; Naya, S. Chem. Soc. ReV. 2009, 38, 1849.
14) Kiyonaga, T.; Mitsui, T.; Torikoshi, M.; Takekawa, M.; Soejima, T.; Tada,
H. J. Phys. Chem. B 2006, 110, 10771.
d
d d
is larger than k
(15) S a´ nchez-S a´ nchez, C. M.; Bard, A. J. Anal. Chem. 2009, 81, 8094.
(16) Balbuena, P. B.; Calvo, S. R.; Lamas, E. J.; Salazar, P. F.; Seminario, J. M.
J. Phys. Chem. B 2006, 110, 17452.
(17) Weiher, N.; Beesley, A. M.; Tsapatsaris, N.; Delannoy, L.; Louis, C.; van
Bokhoven, J. A.; Schroeder, S. L. M. J. Am. Chem. Soc. 2007, 129, 2240.
F
2
0
2
shift of Au NPs loaded on TiO .
1
8
E
F
d
3
(
18) Kiyonaga, T.; Fujii, M.; Akita, T.; Kobayashi, H.; Tada, H. Phys. Chem.
Chem. Phys. 2008, 10, 6553.
2
21
(19) Kiyonaga, T.; Jin, Q.; Kobayashi, H.; Tada, H. ChemPhysChem 2009, 10,
2
-catalyzed CO oxidation. The decrease
2
935.
(20) Tada, H.; Soejima, T.; Ito, S.; Kobayashi, H. J. Am. Chem. Soc. 2004,
26, 15952.
d
1
(
21) (a) Molina, L. M.; Rasmussen, M. D.; Hammer, B. J. Chem. Phys. 2004,
120, 7673. (b) Remediakis, I. N.; Ropez, N.; Nørskov, J. K. Angew. Chem.,
Int. Ed. 2005, 44, 1824.
d
F
2
O
2 2
JA102651G
J. AM. CHEM. SOC. 9 VOL. 132, NO. 23, 2010 7851