Au/TiO2 photocatalysts prepared by solid grinding for artificial solar-light water splitting

Article abstract of DOI:10.1039/c5nj03053f

Here we show in an innovative way that solid grinding is a simple and alternative method for the preparation of solar-light active Au/TiO₂ photocatalysts. We use, for the first time in the solid grinding method, triphenylphosphine gold(i) chloride (AuPPh₃Cl), which has recently been used in solution-based gold catalysts preparation, and chloroauric acid (HAuCl₄), instead of dimethyl gold(iii) acetylacetonate [Me₂Au(acac)] as gold precursor. Both compounds yield Au/TiO₂ nanocomposites with interesting activity for artificial solar-light water splitting. In this paper we establish that solid grinding approach to elaborate Au/TiO₂ photocatalyst leads to better photocatalytic activity toward artificial solar light water splitting than using chemical reduction method. Effects of the gold loading, of the gold precursor and of the calcination temperature on the photocatalytic activity are described and discussed. The impact of calcination temperature is highlighted; calcination at 400 °C is found to be the optimal temperature leading to a strong interaction and intimate contact between Au and TiO₂ nanoparticles, thus allowing beneficial electronic effects.

Full text of DOI:10.1039/c5nj03053f

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ARTICLE
Au/TiO
2
photocatalysts prepared by solid grinding for artificial solar-light water
splitting
Received 00th January 20xx,
Accepted 00th January 20xx
Clément Marchal, Matthieu Behr, Fabrice Vigneron, Valérie Caps, Valérie Keller*
DOI: 10.1039/x0xx00000x
www.rsc.org/
ICPEES, Institute of Chemistry and Processes for Energy, Environment and Health, UMR 7515
CNRS/University of Strasbourg, 25 rue Becquerel, 67087 Strasbourg cedex, France
Here we show in an innovative way that solid grinding is a simple and alternative method for the preparation
of solar-light active Au/TiO2 photocatalysts. We use, for the first time in the solid grinding method,
3
triphenylphosphine gold (I) chloride (AuPPh Cl), which has recently been used in solution-based gold
catalysts preparation, and chloroauric acid (HAuCl ), instead of dimethyl gold (III) acetylacetonate
4
[
Me
artificial solar-light water splitting. In this paper we establish that solid grinding approach to elaborate
Au/TiO photocatalyst led to better photocatalytic activity toward artificial solar light water splitting than
2 2
Au(acac)] as gold precursor. Both compounds yield Au/TiO nanocomposites with interesting activity for
2
using chemical reduction method. Effects of the gold loading, of the gold precursor and of the calcination
temperature on the photocatalytic activity are described and discussed. The impact of calcination
temperature has been highlighted; calcination at 400°C has been found to be the optimal temperature
leading to a strong interaction and intimate contact between Au and TiO
beneficial electronic effects and stabilization of Au nanoparticles.
2
nanoparticles, thus allowing
2
0-23
efficiency of photocatalytic water splitting reaction.
The impact
Introduction
of the presence of a noble metal co-catalyst depends on many
factors such as the nature of the metal, its content as well as the
way of deposition. The enhancement of the photocatalytic activity
has also been attributed to the formation of a Schottky barrier at
the metal/semi-conductor interface, which leads to electron
Sustainable hydrogen production systems are of great importance
for the future. Nowadays, more than 90% of the present hydrogen
needs are covered by steam reforming of methane, a non-
renewable source. Photocatalysis, with its potential to use sunlight
for generating hydrogen, represents one of the promising
technologies for clean and environmentally friendly hydrogen
production and provides a way to use sunlight for generating
2
4
trapping and efficient charge separation.
2
0
Bamwenda et al.
compared hydrogen production from water-
ethanol solution using different kinds of Au-loaded TiO . Different
2
hydrogen as a renewable green fuel. Since the discovery of metal particle deposition methods, such as deposition–
photocatalytic water splitting on semi-conductor catalysts by precipitation, impregnation and photodeposition were also tested.
1
Fujishima and Honda, much effort has been put in the It was found that Au loading prepared by photodeposition worked
development of photocatalysts that are able to harvest solar energy better than prepared by deposition–precipitation and
and to convert it into chemical energy. More precisely, a lot of impregnation. The variations might be explained by the better
studies are dealing with TiO
efficiency toward water splitting under solar light illumination.
2
-based photocatalysts with improved contact with TiO2 active sites for photodeposition method. The
2–6
2
photocatalytic activity for water splitting on Au-loaded TiO seems
The improvement of its photocatalytic water splitting performance
can be achieved by many strategies. Amongst them, we can found
to be sensitive to the preparation method. Furthermore, too much
metal particle deposition might reduce photon absorption by TiO
2
and might also become electron-hole recombination centers,
resulting in lower efficiency.
7
,8
9-11
12-14
cationic, anionic
band gap energy, addition of electron donors (hole scavengers),
and establishment of heterojunctions between TiO and a lower
in order both to photosensitize into
or co-doping
approaches to narrow the
15,16
2
1
7-19
Solid grinding (SG) is a solventless catalyst preparation method. It
has proven a quite useful alternative to wet chemistry processes for
band gap semiconductor
visible light and to reduce the charge carriers recombination.
Moreover, several research works have reported that the
deposition/loading of a precious noble metal, such as Pt, Au, Pd, Rh
on a semiconductor surface is beneficial for greatly enhance the
25-28
29
30
the preparation of a variety of metal,
alloy and mixed oxide
catalysts. In the case of supported metal catalysts, SG consists in
manually grinding and mixing for a short time, typically a few
minutes, a metal precursor with the powder support, using a
mortar and pestle. The operation is carried out at room
temperature. Despite the simplicity of the method, the metal
precursor is successfully dispersed, at the molecular scale, over the
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support. After reduction, often achieved by thermal treatments, loading in wt.% keeping in mind that a deposition yield of 85% was
supported metal nanoparticles are obtained. All the metal initially achieved.
introduced as metal complex (or metal salt) is incorporated in the
final catalyst, which is of economic significance especially in the Characterization
case of precious metals such as gold. Besides, despite the absence
X-ray Diffraction (XRD) measurements were carried out on a D8-
Advance diffractometer equipped with a LynxEye detector and
operated at 40 kV and 40 mA, in a θ - 2θ mode using the Kα1
radiation of Cu at 1.5406 Å. The datasets are acquired in step-scan
and other mode over the 2θ range 5 – 90°, using a step interval of 0.041° and
a counting time of 94.5s per step. Samples are deposited on a
round-shaped glass plate. The datasets are acquired in step-scan
of solubilization of the metal precursor, high reproducibility is
achieved. Hence, this practical method has proven convenient and
efficient in producing highly active supported gold catalysts for
heterogeneous reactions, such as e.g. the epoxidation of
2
6
27,28
propylene, the aerobic oxidation of glucose
2
5
alcohols
.
In this paper, we carried out as an innovative approach the mode over the 10-90° 2θ range. Average size of the titania
elaboration of Au/TiO photocatalyst for efficient artificial solar light crystallites is determined using the Scherrer formula from the full
2
water splitting using SG preparation method.
width at half-maximum of the TiO (101) reflection at 2θ = 25.3°.
2
Experimental
Thermo-Gravimetric Analysis (TGA) was performed using a TA
Instrument Q5000IR. Each sample was placed in a platinum crucible
and heated from room temperature to 900 °C with a heating rate of
Materials and syntheses
-1
3
-1
1
0 °C min under air flow at 100 cm min .
Titanium (IV) isopropoxide (Ti[OCH(CH
from Sigma-Aldrich. Gold (III) chloride hydrate (HAuCl
trace metals basis) and Chloro-(triphenylphosphine) gold (I) Teller (BET) and t-plot methods. The surface area measurements
AuPPh Cl) (≥ 99.9% trace metals basis) were also purchased from were performed on a Micromeritics Asap 2420 porosimeter using
Sigma-Aldrich. All the chemicals were used without further N as an adsorbent at liquid nitrogen temperature. Materials were
3
)
2
]
4
) (≥ 97%) was purchased
4
) (99.999% Specific surface areas were obtained via the Brunauer, Emett and
(
3
2
purification.
outgassed at 250 °C for 3 h in order to desorb impurities from their
surfaces.
Titania (TiO
2
) “sol-gel” was obtained via a “low temperature”
synthesis. First, an amount of titanium isopropoxide (TIP) precursor
was mixed with 40 mL of ethanol at room temperature. To this
solution, 40 mL of water (adjusted to pH = 9, by addition of
ammonia) was added dropwise. Then, the solution was evaporated
under stirring until a dry paste was obtained and dried overnight at
The diffuse-reflectance UV-Visible absorption spectra of composites
were recorded on a Cary UV 100 Scan UV/Vis spectrophotometer
(
Varian).
Photocatalytic study
1
10 °C. To finish, the obtained sample was crushed in an agate
-1
mortar and calcined at 400 °C for 3 h (heating rate of 5 °C min ).
The photocatalytic activity of the prepared samples was evaluated
toward the water-splitting reaction. Hydrogen production was
carried out in a Quartz reactor containing 1 L of Milli-Q water and
equipped with a plunging quartz tube containing a 150 W CERAMIC-
Metal-Halide Lamp (light emission spectra shown in Figure 1) with a
low UV-A content and a large part in the visible light range. This
artificial light is used in our experimental conditions for simulating
Au/TiO
2
nanocomposites were prepared by solid grinding. Titania
Cl (unless
(
from the sol-gel synthesis, 500 to 1500 mg) and AuPPh
3
otherwise mentioned, 1.3 to 13 mg) were mechanically mixed with
a pestle in an agate mortar during 10 min at room temperature
(
3
about 22 °C). The amount of AuPPh Cl was adjusted in order to
tune gold loadings from 0.1 wt.% to 1 wt.%. Finally, a calcination
step was applied. Calcinations were performed at 200 °C, 400 °C,
and 600 °C in order to see the effect of the calcination temperature
on the structural and functional properties of the composites. The
resulting materials are denoted XAu/TiO
the gold loading in wt.% and Tcal stands for the calcination
temperature in °C. Three samples were also prepared with HAuCl
2
solar-light irradiation. The measured irradiance was 30 mW/cm .
The photocatalytic tests were performed with 250 mg of catalyst
-1
under 100 mL min nitrogen flow with a mechanical stirring at 700
rpm. Prior to any experiment, residual oxygen was removed by
nitrogen flushing. Pure water was used as hydrogen source and
2
[Tcal], where X stands for
4
(
5-13 mg) instead of AuPPh Cl as gold precursor. These samples are
3
denoted as XAu[HAuCl
4
]/TiO
2
[Tcal].
For comparison, two Au/TiO
2
nanocomposites were also prepared
by chemical reduction, adapting the procedure described in ref. 31.
Titania (500 mg) was dispersed into ethanol with a tip sonicator (25
-3
-1
4 0
kHz) during 30 min. A HAuCl solution (C =2.5(±0.2)×10 mol L )
was added, the volume of which (1.8 mL or 3.1 mL) was adjusted
according to the targeted gold loading (0.3 wt. % or 0.5 wt. %). The
resulting mixture was left in a bath sonicator (30 W, 35 kHz) for 1 h
-2
-1
4 0
before 5 mL of a fresh NaBH solution (C =2.5×10 mol L ) was
added. The mixture was then sonicated during 2 h. To finish,
samples were dried at 110 °C during 12 h. These samples are
Wavelenghts, nm
Figure 1: Emission spectrum of the artificial solar light (metal halide 150
W)
denoted XAu/TiO (CR), where X stands for the theoretical gold
2
methanol was added as sacrificial agent (0.1 to 1% volumetric) to
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enhance H production. The reaction products were analyzed on-
ARTICLE
2
line every 100 s by thermal conductivity detectors (TCD) on a micro-
gas chromatography Gaz Analyser R-3000 SRA Instruments. All
experiments were performed under the same conditions.
Results
2
All Au/TiO nanocomposites used in this study exhibit a purple color
indicative of the presence of gold nanoparticles (Au NP) in the
samples. For the series of composites prepared by solid grinding,
the shade of purple intensifies with increasing gold loading,
showing the presence of more gold within the composite.
Influence of the gold loading
4 2
Figure 3: Impact of the gold loading of Au[HAuCl ]/TiO [200]
nanocomposites on the amount of hydrogen produced in the water
splitting reaction carried out in the presence of 1, 5, or 10 mL of methanol.
2
Figure 2 shows the influence of the gold loading of Au/TiO [200]
nanocomposites on the amount of hydrogen evolved from water
splitting as a function of the amount of sacrificial agent. It can be
seen that, whatever the amount of methanol present, increasing
the gold loading from 0.1 to 0.2 wt.% doubles the activity of the
composite. The production of hydrogen is again nearly doubled by
further increasing the gold loading to 0.5 wt.%. Nearly 470 µmol of
(
Figure 2). Increasing the gold loading to 0.6 wt.% however leads to
a 30% loss of the photocatalytic activity of the Au[HAuCl ]/TiO [200]
4
2
composite (carrying out the reaction with 10 mL methanol).
H are produced per hour per gram on the 0.5Au/TiO [200] sample
in the presence of 10 mL of methanol. Further increasing the
loading of gold to 1 wt.%, on the other hand, results in a major
2
2
Hence, a gold loading of 0.5wt.% seems optimal to boost the
photocatalytic activity of titania in water splitting, whatever the
gold precursor used in solid grinding. It must be noted that, for a
2
decrease of the photocatalytic activity of about 60%. 1Au/TiO [200]
4
final calcination at 200°C, using HAuCl leads to a slightly higher
remains only 50% more active than 0.1Au/TiO2[200]. This is
attributed to enhanced recombination of the charges produced by
the semi-conductor at the possibly more numerous metal
activity than using AuPPh Cl as precursor. Any larger loading of gold
markedly reduces the catalytic enhancement.
3
22
2
nanoparticles/TiO interface. The gold loading comprised between
Influence of the atmosphere of the post-synthesis treatment of
HAuCl /TiO mechanical mixtures
0
.5 and 1 wt.% have not been investigated. Hence, amongst the
4
2
photocatalytic systems studied here, 0.5 wt.% appears to be the
optimal loading of gold for efficiently splitting water and maximizing
hydrogen production under our conditions. Similar metal loadings
have proven beneficial to enhance the photocatalytic activity of
Using hydrogen instead of air, during thermal treatment of the
mechanical mixtures of HAuCl and TiO at 200°C, does not result in
any improvement in the photocatalytic activity of the resulting
composite (Figure 4). Hydrogen treatment is actually detrimental to
4
2
2
2
titania in other studies.
4 2
the activity: 0.5Au[HAuCl ]/TiO [200] in particular loses up to 30%
of its activity if treated under hydrogen instead of air. This effect is
slightly less pronounced in the case of 0.3Au[HAuCl ]/TiO [200], but
4 2
it is still present.
2
Figure 2: Impact of the gold loading of Au/TiO [200] nanocomposites on
the amount of hydrogen produced in the water splitting reaction carried
out in the presence of 1, 5, or 10 mL of methanol.
Figure 4: Impact of the atmosphere of the thermal treatment of
Au[HAuCl ]/TiO [200] nanocomposites on the amount of hydrogen
produced in the water splitting reaction carried out in the presence of 1, 5
and 10 mL of methanol.
4
2
The same trend can be observed with the composites prepared
4
with HAuCl (Figure 3): 0.5 wt% Au appears to be the optimal
loading, although the difference between 0.3 and 0.5 wt% is less
pronounced than for the composites prepared with AuPPh
3
Cl
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Influence of the calcination temperature of AuPPh
mechanical mixtures
3
Cl/TiO
2
After grinding the TiO
2 3
“solgel” material with AuPPh Cl and calcining
the mixture at 200°C, an increase in the surface area (from 117 to
2
-1
1
40 m g ) is observed (Table 1). This was rather unexpected since
Figure 5 shows the influence of the calcination temperature of titania was already calcined at 400 °C prior to its introduction in the
Au/TiO nanocomposites on the amount of hydrogen evolved from grinding mixture. The action of mechanical grinding at room
2
water splitting. Only the most effective composites, in term of gold temperature, followed by calcination at a mild temperature, is
utilization, are presented. Besides, only the results obtained in the unlikely to reduce the intrinsic size of the anatase crystallites. This is
presence of 10 mL methanol, which allows to get the highest indeed confirmed by calculation of the average size of the titania
hydrogen productions under our conditions, are shown. It appears crystallites as derived from XRD spectra (Figure 6), using the Debye-
that, whatever the gold loading of the composite, calcining the Scherrer formula on the intense TiO
mechanical mixtures of AuPPh Cl and TiO at 400 °C yields the anatase crystallites contained in the starting TiO
largest amounts of hydrogen, as compared with the calcinations unchanged upon solid grinding with AuPPh Cl and calcination at 200
performed at 200 °C and 600 °C. It is also interesting to mention °C. To account for the non-negligible increase in surface area, we
that whatever the calcination temperature, 0.5Au/TiO remains the must thus assume that 0.5Au/TiO [200] contains a certain amount
most active composite. Its activity of about 470 ꢀmol H
of organics, which must have been introduced upon mixing with
can be boosted by about 25% by increasing the calcination AuPPh Cl. It implies that calcination at 200 °C does not lead to the
temperature from 200 to 400 °C. 0.5Au/TiO
[400] thus yields 590 complete reduction of gold and that ligands (or products of their
cata . It surpasses the composites prepared from decomposition) still persist in 0.5Au/TiO [200], as will be evidenced
mechanical mixtures of HAuCl and TiO (Figure 3).
and discussed below, in the TGA section. After calcination at 400 °C,
the composite retrieves the surface area of the starting TiO
solgel” and the average anatase crystallite size remains
2
(101) reflection: the size of the
3
2
2
“solgel” is
3
2
2
-
1
-1
cata
2
h g
3
2
-1
-1
ꢀmol H
2
h
g
2
4
2
2
“
unchanged. Hence, it can be concluded that calcination at 400 °C
only mildly affects the structural and morphological properties of
the composite. However, calcination at 600 °C causes a drastic
2
-1
decrease in surface area (from 121 to 38 m g ), associated with an
increase in the average size of the anatase crystallites, which is
3
2-34
typical of the behavior of oxides.
The increase in crystallite size
is however moderate compared to the loss of surface area, which
suggests that some aggregation has occurred during the process.
The rutile phase has also been formed as evidenced by XRD (Figure
6
).
Figure 5: Impact of the calcination temperature of Au/TiO
2
nanocomposites on the amount of hydrogen produced in the water
splitting reaction carried out in the presence of 10 mL of methanol.
2
In summary, 0.5Au/TiO [400] is the best composite of the study, in
terms of photocatalytic hydrogen production from water splitting.
-1
-1
2
Its activity reaches 590 ꢀmol H h gcata in the presence of 10 mL
of methanol. In the next section, we will present the structural
parameters leading to such photocatalytic performance, which will
allow us to hypothesize on the reasons for the optimal efficiency of
3 2
calcining AuPPh Cl/TiO mechanical mixtures at 400 °C.
Discussion
Effect of calcination on the physico-chemical properties of Au/TiO
2
Figure 6: (a) Diffractograms of TiO
temperatures, showing anatase TiO
reflections. The diffractogramm of the parent TiO
comparison.
2
and 0.5Au/TiO
2
calcined at different
) and gold (
2
“solgel” is shown for
2
(ꢀ
), rutile TiO
2
(
ꢁ
ꢂ)
-
1
Samples
TiO “solgel”
S
BET (m²g )
Crystallite size (nm)
Anatase
18.1
Rutile
/
2
117
Concerning the gold component of the composite, the presence of
the surface plasmon resonance (SPR) in the absorption spectra of all
Au/TiO2 composites (Figure 7) is a clear indication that gold is
present as nanoparticles. While the SPR is positioned at about 550
nm for the composites calcined at 200 °C (Figure 7a), it shifts to
about 580 nm when calcination is performed at 400 °C (Figure 7b)
0
0
0
.5Au/TiO
.5Au/TiO
.5Au/TiO
2
2
2
[200]
[400]
[600]
140
121
38
17.9
17.2
24.5
/
/
45
2
Table 1: Physico-chemical properties of 0.5Au/TiO , including surfaces
areas (SBET) and titania crystallite sizes, as derived from XRD using the and to about 600 nm (Figure 7c) when the calcination is performed
Debye-Scherrer formula.
at 600 °C. This red-shift (Figure 7d) is typical of an increase in the
refractive index of the composite. This is consistent with the
4
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increase in the crystallinity of the titania component of the
ARTICLE
c)
35
composite observed by XRD (Figure 6). Besides, the intensity of
the SPR appears only mildly affected by increasing the calcination
temperature from 200 to 400 °C. However, further increasing the
calcination temperature to 600 °C results in a clearly more intense
SPR band. This suggests that the size of the gold nanoparticles (Au
2
NP) initially present in the Au/TiO [200] composites has markedly
increased upon calcination at 600 °C. This is generally observed at
these temperatures, due to the relatively low melting point of gold
3
6
(
1064 °C) and the resulting low Tammann temperature of Au NP.
Actually, the low intensity of the SPR band exhibited by the
composites calcined at 400 °C, associated with a broad and weak Au
(
200) reflection in the XRD spectrum (Figure 8), indicates that Au NP
are well-stabilized within the composites. Hence, the sintering,
which leads to a marked increase in Au NP size and which is often
observed at this temperature in Au/TiO
2
catalysts prepared by
3
7,38
other methods,
has also been evidenced in our case, looking at
the TEM particles size distribution (Figure 9).
d)
a)
2 2
Figure 7: UV-vis. spectra of Au/TiO [200] (a), Au/TiO [400] (b) and
Au/TiO
2
[600] (c). Impact of the calcination temperature on the
(d)
absorption spectrum of 0.5Au/TiO
2
b)
Finally, thermogravimetric analysis of 0.5Au/TiO [200] (Figure
2
1
and 450 °C. It is attributed to the reduction of AuPPh Cl into
0a) clearly shows a weight loss of about 0.7% between 350
3
2
Au NP. Given that the synthesis of 0.5Au/TiO [200] involves 6.7
mg of AuPPh Cl (i.e. 3.55 mg of PPh ) for 500 mg TiO , the
2
3
3
composite thus initially contains 0.71 wt% of PPh
ligands are thus retained in the composite calcined at 200 °C,
3
. All PPh
3
3
9
most probably located at the outer surface of the Au NP. It
thus looks like calcination at 200 °C does not lead to complete
reduction of gold, in the sense that surface gold atoms might
+
-
remains as [AuPPh ] [Cl] in 0.5Au/TiO [200]. Gold is however
3
2
reduced in the bulk of the particle in agreement with UV
evidence for the presence of Au NP (Figure 7). Besides,
considering that the decomposition of PPh
2
3
is completed by
20 °C in a dynamic calcination process (Figure 10b), and that
3
the decomposition of bulk/free AuPPh Cl is completed by 250
°
C under such conditions, it seems that AuPPh Cl/PPh3 is
3
stabilized in the composite enough to shift its full
decomposition temperature by 200 °C (under dynamic
conditions). Hence calcination at 400 °C (maintained for 4 h) is
needed in order to fully decompose the gold complex and its
ligands.
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efficient role of Au NP as co-catalyst benefits from a better impact
both (i) on the co-catalyst role of Au NP and on (ii) the
metal/semiconductor interface (Figure
1
1
1
00
a)
b)
c)
9
9
9
9
9
9
8
7
6
5
1
1
1
00
00
00
300
200
300
500
700
400
700
900
500
900
Figure 8: Diffractograms of 0.5Au/TiO
2
calcined at different temperatures,
Temperature (°C)
highlighting the Au (111) and Au (200) reflections at 38.2° and 44.5°
respectively ( ).The diffractogramm of the parent TiO “solgel” is shown
for comparison.
ꢂ
2
00
80
60
40
20
0
300
Temperature (°C)
00
9
9
9
9
9
9
8
7
6
5
Figure 9: Au mean size particles distribution of Au/TiO
2
[600] composites
The TGA profile of 0.5Au/TiO [400] (Figure 10a) is subsequently
2
similar to that of TiO
2
(Figure 9c), indicating indeed the absence of
AuPPh Cl/PPh in the material. It seems that full reduction of gold,
3
3
achieved by calcining the mechanical mixtures of AuPPh
at 400 °C, allows to maximize the photocatalytic activity of the
composite in the water splitting reaction. While PPh residues at
the proximity of Au NP are useful for stabilizing Au NP size, their
presence proves detrimental to the photocatalytic activity of
3 2
Cl and TiO
3
500
Temperature (°C)
titania. A negative impact of the presence of PPh residues has also
3
been observed in Au/silica catalysts used for the aerobic
epoxidation of stilbene. In this case, accessibility of part of the
catalytic Au surface is clearly blocked. In photocatalytic processes,
Figure 10: TGA of 0.5Au/TiO
2
2 3
[200] (---) and 0.5Au/TiO [400] (a), PPh (---)
4
0
and AuPPh Cl (b) and TiO (from the sol-gel synthesis) (c)
3
2
on the other hand, we speculate that these residues might prevent photogenerated electron transfer from activated TiO to Au NP
2
+
direct contact between Au NP and titania, thus inhibiting favorable leading to catalytic H reduction into H2 on the metal NP. The
electronic effects for photocatalytis. Direct, strong interaction enhancement of photocatalytic activity due to close contact of the
between Au NP and titania might indeed be key for Au NP to two components can also be attributed to the formation of a
enhance the activity of TiO photocatalysts. We suppose that the Schottky barrier at the metal/semi-conductor interface, which leads
2
2
intimate contact between Au NP and TiO surface has a strong to electron trapping on Au NP and thus efficient charge separation
impact both (i) on the co-catalyst role of Au NP and on (ii) the limiting recombination phenomena.
6
| J. Name., 2012, 00, 1-3
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NP lee wa s eJ od uo r nn oa tl aod fj uC s ht em ma ri sg it nr sy
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DOI: 10.1039/C5NJ03053F
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ARTICLE
residues. Calcination at 400°C has been found to be the optimal
temperature leading to a strong interaction and intimate contact
between Au and TiO
beneficial electronic effects. Indeed we suppose that the intimate
contact between Au and TiO nanoparticles induces
photogenerated electron transfer from TiO to Au NPs yielding
2
nanoparticles. This strong interaction helps to
2
2
enhanced co-catalyst activity and better charges separation. These
two positive effects can explain the enhanced photocatalytic
activity toward solar light water splitting to produce H .
2
Acknowledgements
The authors acknowledge the Region Alsace for financial support
and Dr. Anne Boos (IPHC Strasbourg) for ICP analyses.
2
Figure 11: Au/TiO intimate junction. Au NP act as co-catalyst and for
enhancing photogerated charges separation.
References
Comparison between solid grinding and chemical reduction
1
2
3
.
.
.
A. Fujishima and K. Honda, Nature 1972, 238, 37.
Z. Zou, J. Ye and K. Sayama, Nature 2001, 414, 625.
R. Abe, T. Takata, H. Sugihara and K. Domen, Chem. Comm., 2005,
The activity of the Au/TiO nanocomposites elaborated via the solid
grinding method was compared to that of Au/TiO photocatalysts
2
2
prepared by chemical reduction method (Figure 12). It must be
highlighted that for Au loadings ranging below 0.5 wt.%, chemical
reduction led to lower photocatalytic activity towards artificial solar
light water splitting. Hydrogen production rates indeed appear at
least 40% lower than using the composites prepared by solid
3
829.
4
.
P. Dhanasekaran and N.M. Gupta, Int. J. Hydrogen Energy, 2012,
37, 4897.
K.M. Parida, K.H. Reddy, S. Martha, D.P. Das and N. Biswal, Int. J.
Hydrogen Energy, 2010, 35, 12161.
5.
6
7
.
.
M. Ashokkumar, Int. J. Hydrogen Energy, 1998, 23, 427–38.
W.Y. Choi, A. Termin and M.R. Hoffmann, J. Phys. Chem., 1994,
grinding, whether starting from AuPPh
3 4
Cl (Figure 2) or using HAuCl
(
Figure 3). The gold loadings, on the other hand, are only 15% lower
8
4, 13669.
than those of the solid grinding samples. Given the effect of the
calcination temperature of the photocatalytic activity described
previously, the lower activity of the CR samples may come from the
8
9
1
1
.
D. Dvoranova, V. Brezova, M. Mazur and M. Malati, Appl Catal B:
Environ, 2002, 37, 91.
R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki and Y. Taga, Science,
.
2
001, 293, 269.
0.
1.
T. Ohno, M. Akiyoshi, T. Umebayashi, K. Asai, T. Mitsui and M.
Matsumura, Appl Catal A: Gen, 2004, 265,115.
M. Ni., M. K.H. Leung, D. Y. C. Leung and K. Sumathy, Renewable
and Sustainable Energy Reviews, 2007, 11, 401.
1
1
2.
3.
R. Long and N.J. English, Chem. Phys. Lett., 2009, 478.
W.-J. Yin, H. Tang, S.-H. Wei, M. M. Al-Jassim, J. Turner and Y.
Yan, Phys. Rev. B 2010, 82, 045106.
1
1
4.
5.
T. Cottineau, N. Béalu, P.-A. Gross, S.N. Pronkin, N. Keller, E.R
Savinova and V. Keller, J. Mater. Chem., 2013, 1, 2151.
A.A. Nada, M.H. Barakat, H.A. Hamed, N.R. Mohamed, T.N.
Veziroglu, Int J Hydrogen Energy, 2005, 30, 687.
1
1
6.
7.
Y.X. Li, G.X. Lu, S.B. Li, Chemosphere, 2003, 52, 843.
K. Gurunathan, P. Maruthamuthu and V.C. Sastri, Int. J. Hydrogen
Energy, 1997, 22 57.
1
1
2
2
2
2
2
2
8.
9.
0.
1.
2.
3.
4.
6.
P. Dhanasekaran and N.M. Gupta, Int. J. Hydrogen Energy, 2012,
absence of thermal treatment in the CR method.
Figure 12: Impact of the gold loading of Au/TiO (CR) nanocomposites on
2
the amount of hydrogen produced in the water splitting reaction carried
out in the presence 1, 5, or 10 mL of methanol.
3
7, 4897.
K.M. Parida, K.H. Reddy, S. Martha, D.P. Das and N. Biswal, Int. J.
Hydrogen Energy 2010, 35, 12161.
G.R. Bamwenda, S. Tsubota, T. Nakamura and M. Haruta. J
Photochem Photobiol A: Chem 1995, 89,177.
S. Sakthivel, M.V. Shankar, M. Palanichamy, B. Arabindoo, D.W.
Bahnemann and V. Murugesan, Water Res., 2004, 38, 3001.
O. Rosseler, V.S. Muthukonda, M. Karkmaz-Le Du, L. Schmidlin, N.
Keller and V. Keller, J. Catal., 2010, 269, 179.
Conclusion
In this paper we highlighted the interest of solid grinding as simple
M.C. Blount, J.A. Buchholtz and J.L. Falconer, J. Catal., 2001, 197,
an innovative approach for the elaboration of Au/TiO
photocatalysts for H production by artificial solar light water
splitting. We used, for the first time in the solid grinding method,
triphenylphosphine gold (I) chloride (AuPPh Cl) as Au precursor.
Using this precursor, it has been shown that a final calcination step
2
3
03.
M. Ishida, M. Nagaoka, T. Akita and M. Haruta, Chem. Eur. J.,
008, 14, 8456.
2
2
3
J. Huang, T. Akita, J. Faye, T. Fujitani, T. Takei and M. Haruta,
Angew. Chem. Int. Ed., 2009, 48, 7862.
higher than 250°C is required to completely eliminate AuPPh
3
Cl
27.
H. Okatsu, N. Kinoshita, T. Akita, T. Ishida and M. Haruta, Appl.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
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Please do not adjust margins
New Journal of Chemistry
Page 8 of 9
View Article Online
DOI: 10.1039/C5NJ03053F
ARTICLE
Journal Name
Catal. A, 2009, 369, 8.
2
2
3
3
3
3
3
3
3
8.
9.
0.
1.
2.
3.
4.
5.
6.
T. Ishida, H. Watanabe, T. Bebeko, T. Akita and M. Haruta, Appl.
Catal. A, 2010, 377, 42.
J. Kugai, T. Moriya, S. Seino, T. Nakagawa, Y. Ohkubo, H. Nitani
and T. A. Yamamoto, Catal Lett., 2013, 143, 1182.
H. Zhu, D.C. Rosenfeld, D.H. Anjum, V. Caps and J.-M. Basset,
ChemSusChem, 2015, 8, 1254.
F. Vigneron, A. Piquet, W. Baaziz, P. Ronot, A. Boos, I. Janowska,
C. Pham-Huu, C. Petit and V. Caps, Catal. Today, 2014, 235, 90.
H. Zhu, S. Ould-Chikh, D. H. Anjum, M. Sun, G. Biausque, J.-M.
Basset and V. Caps, J. Catal., 2012, 285, 292.
P. Laveille, G. Biausque, H. Zhu, J.-M. Basset and V. Caps, Catal.
Today, 2013, 203, 3-9.
H. Zhu, H. Dong, P. Laveille, Y. Saih, V. Caps and J.-M. Basset,
Catal. Today, 2014, 228, 58.
P. Lignier, M. Comotti, F. Schüth, J.-L. Rousset and V. Caps, Catal.
Today, 2009, 141, 355 and references therein.
V. Caps, L’Actualité Chimique, 2010, 337, 18 and references
therein.
3
3
7.
8.
V. Mendez, V. Caps and S. Daniele, Chem. Commun., 2009, 3116.
V. Mendez, K. Guillois, S. Daniele, A. Tuel and V. Caps, Dalton
Trans., 2010, 39, 8457.
3
4
9.
0.
Y. Liu, H. Tsunoyama, T. Akita and T. Tsukuda, J. Phys. Chem. C,
2
009, 113, 13457.
K. Guillois, L. Burel, A. Tuel and V. Caps, Appl. Catal. A, 2012, 415-
16, 1.
4
8
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Page 9 of 9
New Journal of Chemistry
H2O
H2 + ½ O2
Calcining mechanical mixtures of TiO2
and AuPPh Cl generates Au/TiO
3
2
nanocomposites with strong Au-TiO2
interaction and high solar light activity.
Au/TiO2
nanocomposite
2
0 nm