ORIGINAL PAPER

Effect of Gold Particle Size and Deposition Methodon the Photodegradation of 4-Chlorophenol by Au/TiO2

S. Oros-Ruiz • J. A. Pedraza-Avella •

C. Guzman • M. Quintana • E. Moctezuma •

G. del Angel • R. Gomez • E. Perez

Published online: 19 January 2011

� Springer Science+Business Media, LLC 2011

Abstract The photoactivity of TiO2 P25 modified by

surface-deposition of gold nanoparticles was investigated

trough the photocatalytic degradation of aqueous 4-Chlo-

rophenol (4-CP). The Au/TiO2 materials were prepared by

three methods: photodeposition, deposition–precipitation

(D–P) and colloidal deposition. Each preparation yields to

different particle size, distribution and properties of gold

nanoparticles. However, the photoactivity of these systems

depends mainly on the gold particle size. All the materials

fit well to a pseudo first order rate model and a relationship

between the kinetic rate and the resulting particle sizes was

found, which shows the importance of the nanoparticle size

in the photoactivity of the TiO2 modified by gold. The

optimal load was found to be 0.5 wt% Au/TiO2 for the

material prepared by D–P, since this material increased

the photoactivity degradation of commercial TiO2 in 80%.

Keywords Titanium dioxide � Gold nanoparticles �Photocatalysis � 4-chlorophenol

1 Introduction

In photocatalysis, the most common material used for the

photodegradation of organic pollutants in aqueous solu-

tions is the titanium dioxide semiconductor, due to its low

cost, chemical and physical stability, availability and no

toxicity. Recently it has been reported that metallic nano-

particles deposited on the TiO2 support improve the

photoactivity of this material. The interaction of metallic

nanoparticles with TiO2 induces modifications in the

electronic state of the solids, leading to important

enhancement of the photocatalytic activity [1]. It has been

reported that gold nanoparticles supported on the surface of

semiconductors present a great catalytic activity for several

reactions [2, 3]. They have also been applied for different

photocatalytic reactions since they increase the separation

of the hole-electron by acting as a sink of electrons, dis-

placing the absorption of light to the visible region and

modifying the surface of the catalyst [4–7]. The use of

noble metal nanoparticles have generated a great interest in

the recent years for many purposes as for catalysis, optical

devices, detection, purification, biosensors and photovol-

taic devices [8–20].

There are several strategies to perform the deposition of

nanoparticles on the TiO2, among the most common

methods to deposit gold nanoparticles on titania are:

S. Oros-Ruiz (&)

Doctorado Institucional en Ingenierıa y Ciencia de Materiales,

Universidad Autonoma de San Luis Potosı, Av. Manuel Nava

No. 6, Zona Universitaria, San Luis Potosı, SLP, Mexico

e-mail: cocoros@dec1.ifisica.uaslp.mx

J. A. Pedraza-Avella

Centro de Investigaciones en Catalisis (CICAT), Universidad

Industrial de Santander (UIS), Sede Guatiguara, Km. 2 vıa El

Refugio, 681011 Piedecuesta (Santander), Colombia

C. Guzman � G. del Angel � R. Gomez

Departamento de Quımica, Area de Catalisis, Grupo

ECOCATAL, Universidad Autonoma Metropolitana-Iztapalapa

(UAM-I), Av. San Rafael Atlixco No. 186, 09340 Mexico, DF,

Mexico

M. Quintana � E. Perez

Instituto de Fısica, Universidad Autonoma de San Luis Potosı,

Av. Manuel Nava No.6 Zona Universitaria, San Luis Potosı,

SLP, Mexico

E. Moctezuma

Facultad de Ciencias Quımicas, Universidad Autonoma de San

Luis Potosı, Av. Manuel Nava No. 6, Zona Universitaria, San

Luis Potosı, SLP, Mexico

123

Top Catal (2011) 54:519–526

DOI 10.1007/s11244-011-9616-y

photodeposition (PD), deposition–precipitation (D–P) and

colloidal deposition (CD). PD is a method that uses UV

light to excite TiO2 and thus generate electrons that promote

the reduction of Au on the titania surface. This method does

not use stabilizing agents and the metallic particles are

formed and deposited on the surface of the TiO2 in aqueous

solution. It requires several washes to eliminate chloride

ions and calcination is not necessary [21]. The D–P method

is commonly used for producing commercial Au catalysts,

in this method the surface of the support acts as a nucleating

agent, and the metal is strongly attached to the support. This

permits the gradual and homogeneous addition of hydroxide

ions throughout the whole solution by the reduction of the

metallic precursor with urea. The D–P method requires

washing and calcination [22]. Finally, the CD method

requires a metal precursor soluble in organic solvents, the

gold nanoparticles are then stabilized by long alkyl thiols

and the TiO2 is added to the solution of these capped

nanoparticles. The metallic nanoparticles are deposited by

weak interactions with the TiO2 support. The method also

requires calcination to remove the organic capping ligands

from the surface [23].

By using these three methods, in the present work we

expect to obtain different gold particle sizes, high metallic

dispersion on the substrate, and different particle shapes.

Our main interest is to evaluate the effect of the nanopar-

ticle deposition method on the photocatalytic behavior of

TiO2. The 4-CP is a model molecule of halogenated aro-

matics; they are used as solvents or reagents in industrial

processes, therefore they are common contaminants in

industrial waste waters [24]. 4-CP is a toxic and recalci-

trant compound that can not be mineralized by traditional

waste water treatment processes, and might be totally

mineralized by advanced oxidation processes as photoca-

talysis. Furthermore 4-CP has been used as a standard for

evaluating various experimental parameters in photocata-

lytic processes [25–27].

2 Experimental Methods

TiO2 Degussa P25 was used as semiconductor in all the

reported experiments. It showed a BET specific surface

area of 56 m2/g, an average particle size of 25 nm, a purity

of 97% and an anatase/rutile ratio of 80/20.

2.1 Photodeposition (PD)

A suspension containing 1 g of TiO2 in 100 mL of Milli-Q

distilled water was prepared in a cylindrical quartz reactor

with ultrasonic agitation for 30 min. HAuCl4 (Aldrich 30

wt%) was added to the suspension to reach the desired

gold loads on the TiO2 (0.25, 0.5, 1.0 and 1.5 wt%). It is

well known that the photocatalytic process involves the

generation of a free electron and a positive hole on the

surface of the semiconductor, they induce reactions of

reduction and oxidation that proceed at the same time. In

order to start the photoreduction of the metallic source, it

is required to provide a reactant to be oxidized; in this

case we used methanol (Caledon 99.8%) in a concentra-

tion 1 M in a final volume of 400 mL [28]. The quartz

reactor was then placed in dark conditions, and deoxy-

genated for 30 min with N2 flow (100 mL/min) in con-

tinuous stirring. The gold deposition was carried out under

constant stirring with UV–Vis radiation provided by four

lamps 15 W with a primary emission at 365 nm. The

solution was filtered after 1 h of irradiation, and the col-

lected material was washed 4 times with 100 mL of

Milli-Q water. The samples were stored at room temper-

ature in dark conditions in a desiccator.

2.2 Deposition–Precipitation (D–P)

This preparation was made in the absence of light. The

deposition of gold was performed with urea (J.T. Baker

99%) following the methodology reported elsewhere [29].

TiO2 (4 g) were dispersed in 100 mL of aqueous HAuCl4(Aldrich 30 wt%) solutions with concentrations corre-

sponding to Au loads of 0.25, 0.5, 1.0, and 1.5 wt% of the

support. Urea was added in a concentration 100 times

higher than that of the HAuCl4 concentration. The sus-

pension was heated at 80 �C and stirred for 8 h. The urea

decomposition led to a gradual rise in the pH of the solu-

tion from 2 to 8. After gold deposition, the solids were

filtered and washed 4 times with 100 mL of Milli-Q water

in order to remove chloride ions which are known to cause

particle sintering. The samples were dried at 80 �C for 12 h

and calcined in air flow (100 mL/min) at 300 �C for 4 h

[29]. The samples were stored at room temperature in dark

conditions in a desiccator.

2.3 Colloidal Deposition (CD)

For this method a metallic source was firstly prepared as

follows: The corresponding to 1 g of HAuCl4 (Aldrich 30

wt%) was dissolved in 50 mL of ethanol (Caledon 95%)

and degassed with N2 for 30 min. Then, a solution of

1.364 g of phosphine (Aldrich 99%) in 50 mL of ethanol,

previously deoxygenated with N2 was added. The reaction

mixture immediately became colorless and a white pre-

cipitate appeared. The mixture was stirred for 2 min and

the product was removed by filtration, washed with diethyl

ether (Fisher 99%) and dried in vacuum. This solid was

dissolved in 10 mL of dichloromethane (Merck 99%), and

60 mL of pentane (Aldrich 99%) were added at 4 �C

resulting in the formation of white needles of

520 Top Catal (2011) 54:519–526

123

chloro(triphenylphosphine)gold that are stable in air and

soluble in organic solvents [30]. The gold nanoparticles in

colloidal suspension were prepared by mixing the

chloro(triphenylphosphine)gold with 0.125 mL of dode-

canethiol (Aldrich 98%) in 50 mL of chloroform (Caledon

98%) forming a clear solution. Tert-butylamine-borane

(Aldrich 99%) was then added in a concentration 10 times

higher than the metallic source. The color of the mixture

gradually darkened and became purple. This synthesis was

made at room temperature and was left for 6 h in constant

agitation under dark conditions. The deposition of these

colloidal metallic particles on TiO2 was made by adding

the support to the solvent containing the gold nanoparticles.

The resulting slurry was decolorated while the color of the

oxide powder was darkened. The solution was stirred for

3 h and the powder was then centrifugated and dried for

12 h at 80 �C. The metallic nanoparticles in the as-pre-

pared metal oxide composites were capped by organic

thiols, these were removed by calcination, for 4 h in air

flow (100 mL/min) at 3008. Stucky et al. reported that after

the calcination, the organic capping ligands are decom-

posed and no sulfur is detected by XPS [31]. The samples

were stored at room temperature in dark conditions in a

desiccator.

2.4 Characterization

The amount of gold deposited was determined by means

of a SpectrAA 220-FS atomic absorption spectrometer.

The XRD was used to identify the TiO2 phases with a

Bruker D-8 Diffractometer using Cu Ka radiation at a step

of 0.03 degrees/min of 2h. The specific surface area was

determined by N2 adsorption using a Quantachrome

sorptometer apparatus. The specific surface areas (BET)

were calculated from the nitrogen adsorption–desorption

isotherms. The UV–Vis spectra of the materials were

obtained in a UV–Vis Diffuse Reflectance Spectropho-

tometer Varian Cary 100. Transmission electron micros-

copy (TEM) was performed in a JEOL JEM 1230 electron

microscope operated at 100 keV. Particle size distribu-

tions were determined by counting at least 200 particles.

Carbon monoxide temperature programmed desorption

(TPD) was carried out to evaluate the dispersion of the

metallic particles using a Chembet-3000 apparatus

equipped with a TCD detector. The sample was reacti-

vated under H2 flow at 300 �C for 1 h. Afterwards the

sample was cooled at room temperature and purged with

He flow for 15 min, then a gas mixture (5%CO/95%He)

was passed through the sample for 1 h. After this time the

sample was purged with He flow for 15 min. The sample

was heated up to 300 �C at a heating rate of 10 �C/min

under a constant He flow of 10 �C/min to induce the

desorption of carbon monoxide.

2.5 Evaluation of the Photocatalytic Activity

in the 4-Chlorophenol Degradation

The evaluation of the photocatalytic activity of the result-

ing materials was made for the degradation of 4-CP, and it

was monitored for a period of 6 h taking the TiO2 P25 as

reference. The reactions were carried out in a well mixed

heterogeneous batch reactor with a UV-PC mercury lamp

of primary emission at 254 nm. The temperature was sta-

bilized at 20 �C with a water recirculation bath connected

to the outer jacket of the reactor. Air was supplied to the

reactor at a constant rate of 100 mL/min using a mass flow

controller. In a typical experiment, the reactor was loaded

with 200 mg of the photocatalyst in 200 mL of 4-CP

solution (40 ppm). To assure the adsorption/desorption

equilibrium, the system was stirred in the dark for 1 h

before turning the UV light on. The progress of the reac-

tion was followed by measuring the disappearance of

the 4-CP as a function of time with a Cary UV–Vis

spectrophotometer.

3 Results and Discussion

The specific surface areas of the solids were obtained in

order to evaluate the modification of the surface due to the

deposition of the metal. The nitrogen adsorption/desorption

isotherms for the materials with the maximum load of gold

for the three preparations were obtained. The specific

surface area obtained for bare TiO2 was 56 m2/g. Degussa

P-25 consists of agglomerates of crystallites, and possess a

low porosity, the surface area is largely external to the

agglomerates and the pore volume measured is mainly

located between the agglomerates (interagglomerate pores)

[32]. The specific surface areas were 56, 46 and 55 m2/g

for the PD, D–P and CD materials respectively, at 1.5 wt%

of Au/TiO2. The BET areas were practically of the same

order in all the samples, which show that no significant

modification of the textural properties of the TiO2 support

were produced due to the deposition of the metal nano-

particles on its surface.

XRD spectra for the bare TiO2 and for the materials at

1.5 wt% Au were recorded. The presence of anatase and

rutile phases can be observed in the materials after gold

deposition. This indicates that no structural effect on the

substrate was made by the different treatments performed

during the gold deposition. The presence of gold is not

detected in the diffractograms since the gold load is very

low. However, the content of gold on the materials was

determined by atomic absorption obtaining a good agree-

ment with the nominal amount of gold on the substrate

(0.25, 0.50, 1.00 and 1.50%). The materials prepared by PD

reported 0.30, 0.60, 1.30 and 2.00 wt%, for the materials

Top Catal (2011) 54:519–526 521

123

prepared by D–P, 0.27, 0.54, 1.20 and 1.40 wt%, and

finally the materials prepared by CD reported 0.20, 0.55,

1.3 and 1.6 wt%.

The optical properties of TiO2 are usually modified by

the presence of gold nanoparticles on the surface. The

UV–Vis absorption spectra for the bare support and the

synthesized gold supported materials are presented in

Fig. 1. A significant enhancement of the absorption due to

plasmon surface resonance (PSR) at 550 nm is observed

due to the interaction of the metallic particles with the

incident light, when this oscillates in the electron conduc-

tion band of the metal, [33]. The band gap appears shifted

to the visible region on the Au/TiO2 samples. The forbid-

den energy levels (Eg) were determined for the TiO2 P25

and for the materials prepared with different gold contents

by diffusive reflectance spectroscopy. The obtained values

are shown in Fig. 2 where the Eg for the bare TiO2 is only

plotted as a reference with a dashed line. As expected, the

band gap is displaced to lower values for the Au/TiO2

semiconductors. The Eg values of the modified materials

are close to each other and it is difficult to establish a

general behavior. However, the Eg decreased for every case

where the deposition of gold was made, and at intermediate

Au contents (1.0 and 1.5 wt% of Au/TiO2), the materials

prepared by D–P showed the lowest Eg value while the

materials prepared by PD presented the highest value.

Kamat et al. [34] have reported that when the semicon-

ductor and metal nanoparticles are in contact the photo-

generated electrons are distributed from TiO2 to the Au

particles, and the transfer continues until the two systems

attain equilibrium. The electron accumulation increases the

Fermi level of Au to more negative potentials, and the

resultant Fermi level gets closer to the conduction band of

the semiconductor, which improves the charge distribution

of the system. Kamat also observed that small Au particles

induce larger shifts in the Fermi level than the large par-

ticles do. This might indicate that the particles obtained by

D–P are smaller than the particles obtained by the other

methods.

The size of the nanoparticles evidently an important

parameter in this discussion, but it is also important in

order to elucidate the effect of the different methods used

here on the photocatalytic activity. Figure 3 shows the

micrographs of the materials at contents of 1.5 wt% of

Au/TiO2 for each deposition method. This concentration

corresponds to the highest value of gold deposition, where a

higher contrast for the different deposition methods can be

seen. The images denote the presence of nanosized metallic

particles. The average diameters and standard deviations

were calculated after counting at least 200 of these particles.

The micrographs (Fig. 3) show some important differences

between the particles synthesized by the three depositions

methods: the particles deposited by the PD and CD pre-

sented large particle size and they are not as well distributed

on the support, whereas the particles deposited by the DP

method (Fig. 3a, c) presented smaller sizes and narrow size

particles, well defined and well distributed on the substrate

(Fig. 3b). The average particle size and the corresponding

standard deviations are plotted as functions of the gold load

in Fig. 4. The D–P method produced particles with smaller

sizes and standard deviations with respect to the other

methods since this deposition method is less sensible to the

variations in the metal load. Otherwise, the particles pre-

pared by CD presented particle size values from 6.8 to

9.3 nm, while the particles prepared by PD had larger

200 300 400 500 600 700 800

Abs

orba

nce

(a.u

.)

Wavelenght (nm)

PD

D-P

CD

TiO2

Fig. 1 UV-Vis diffusive reflectance of solids for bare TiO2 and TiO2

modified with gold nanoparticles by: PD, D–P and CD. The arrowpoint up the increase in gold load 0.25, 0.5, 1.0, and 1.5 wt% of

Au/TiO2

0.25 0.50 0.75 1.00 1.25 1.502.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

Eg

(eV

)

% Au

TiO2

PD

D-P

CD

Fig. 2 Variation of the Eg as a function of Au load. Dashed linerepresents Eg for bare TiO2

522 Top Catal (2011) 54:519–526

123

particle sizes from 7.5 to 12.1 nm and larger standard

deviations.

Another important parameter in the Au deposition is the

dispersion of the metallic particles on the surface of the

TiO2. All the materials analyzed by carbon monoxide TPD

studies indicated that CO is desorbed as a single peak at

temperatures below 100 �C. The results of carbon mon-

oxide desorption also indicated that bare TiO2 adsorbs a

considerable amount of the probe molecule. The amount

adsorbed on the support was subtracted from the amount of

CO chemisorbed on the Au/TiO2 materials under identical

conditions. It has been reported that there is a good

agreement between the mean particle size estimated by

TPD and the mean particle size obtained by TEM, for gold

contents of 2% [35], however, in our case, only those

materials with gold contents of 1.5% presented a good

Fig. 3 TEM images of materials at 1.5 wt% Au/TiO2 prepared by PD (3A), D–P (3B), and CD (3C)

Top Catal (2011) 54:519–526 523

123

agreement between dispersion obtained by TPD and mean

particle size obtained by TEM, probably this technique is not

sensitive enough to determine the dispersion of metal

nanoparticles of our catalysts with gold contents below 1.5

wt%. Therefore, the average particle sizes of the gold

nanoparticles, for all the catalysts were determined by TEM.

In Table 1 are presented the parameters obtained for the

prepared materials: average particle size, constant rate, and

% of 4-CP degraded at half life time. The activities of these

materials are presented in Fig. 5: PD (5A); D–P (5B), and

CD (5C). In the case of PD the material with the highest

activity was the one prepared with 0.25% Au/TiO2, which

improving the degradation rate of the TiO2 P25 in 60%, for

higher depositions (0.5, 1.0 and 1.5% Au/TiO2) in this

method a detrimental effect on the TiO2 activity is

observed. On the other hand, D–P method shows that for

0.25, 0.5 and 1.0% of Au/TiO2, the effect of commercial

TiO2 is improved even by 80% (for the loads of 0.5 and

0.25 0.50 0.75 1.00 1.25 1.500

2

4

6

8

10

12

14

Part

icle

Siz

e (n

m)

% Au

PD

D-P

CD

Fig. 4 Particle size as a function of the Au deposited on the TiO2

Table 1 Comparative results of the Au/TiO2 photocatalysts, gold

particle size, constant rate, % of 4-CP degraded at half life time

Au/TiO2 TEM Constant rate % 4-CP degraded

Catalysts (wt%) Dav (nm) 1/K0 (min) t = 120 min

TiO2 - - 169 52

PD 0.25 7.5 ± 0.9 66 82

PD 0.50 12.2 ± 2.0 556 20

PD 1.00 10.3 ± 1.4 244 36

PD 1.50 9.2 ± 1.0 257 39

D–P 0.25 7.6 ± 1.0 161 55

D–P 0.50 6.1 ± 0.4 39 96

D–P 1.00 6.5 ± 0.4 39 91

D–P 1.50 7.6 ± 0.5 196 51

CD 0.25 6.8 ± 0.9 79 74

CD 0.50 9.3 ± 1.4 159 46

CD 1.00 7.7 ± 0.8 156 59

CD 1.50 9.3 ± 1.0 294 36

0 50 100 150 200 250 300 350 4000.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5 TiO

2

0.25% Au/TiO 2

0.50% Au/TiO 2

1.00% Au/TiO 2

1.50% Au/TiO 2

- ln

(C

/C0)

time (min)

0 50 100 150 200 250 300 350 400

time (min)

0 50 100 150 200 250 300 350 400

time (min)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0 TiO2

0.25% Au/TiO 2

0.50% Au/TiO 2

1.00% Au/TiO 2

1.50% Au/TiO 2

-ln(

C/C

0)

TiO2

0.25% Au/TiO 2

0.50% Au/TiO 2

1.00% Au/TiO 2

1.50% Au/TiO 2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

-ln

(C/C

0)

A

B

C

Fig. 5 Plot of -ln(C/C0) as a function of time for materials prepared

by a PD; b D–P and c CD

524 Top Catal (2011) 54:519–526

123

1.0% Au/TiO2). These materials were the most effective in

the photodegradation of 4-CP of the three evaluated

deposition methods. The photoactivity of the materials

prepared by CD improved significantly at 0.25% Au/TiO2

(53%), and slightly modified with 0.5 and 1.0%. The load

of 1.5% Au/TiO2 was detrimental as in the other methods

used, which indicates that this amount is not effective for

photocatalytic purposes.

The straight lines in Fig. 6 indicate the fitting of the

photocatalytic degradation of 4-CP that show that it fol-

lows approximate first-order kinetics, even after the Au

nanoparticles deposition. This result can be understood in

terms of modified (for solid–liquid reactions) Langmuir–

Hinshelwood kinetics. The degradation was considered to

take place on the semiconductor surface and not on the

gold surface [36]. Gold nanoparticles deposition was very

low in all the cases, thus the mechanism of reaction is not

modified, however, the constant rate is effectively modified

as one can infer from the slope of the fitted line.

The UV light degradation of the 4-CP as a function of

the gold load on the TiO2 is plotted in Fig. 6. It is shown

the activity of TiO2 P25 as a reference, the materials pre-

pared by PD improved the activity of TiO2 only for the one

with 0.25 wt% of Au, those with higher loads produced

larger particle sizes and this conduced to a detrimental

effect. For the materials synthesized by CD, the activity

was improved for those with 0.25, 0.50 and 1.0 wt% Au.

The photoactivity of materials prepared by D–P, presented

a better growing control of the particles, and resulted in the

smaller particles at different loads of gold, which made

them the most active materials for the degradation of the

4-CP presenting a maximum in the activity for the material

at 0.5 wt of Au. It is very interesting to remark that Fig. 6

shows the same behavior that the dependence of the

nanoparticles size as function of the Au loaded (see Fig. 4).

This means that the activity of the materials depends on the

particle size of the metal.

In order to confirm the role of the gold nanoparticles

size, the graph of the inverse of the rate of degradation

(1/K0) as a function of the particle size is shown in Fig. 7.

It can be observed that the average size of the particle has a

strong effect on the degradation rate of the 4-CP. This last

holds despite the chemical modification of the TiO2 pro-

duced by the different deposition methods. It is clear that

the main parameter that rules the photodegradation by TiO2

modified with gold nanoparticles is the particle size.

4 Conclusions

From the results obtained in this work, it is clear that the

particle size exerts an effect of on the activity of the

materials in the photoactivity, beyond the deposition

method, the most important and ruling parameter is the

metal particle size. The materials prepared by D–P were

the most active in the photodegradation of 4-CP since the

particle growth is controlled and prevents the agglomera-

tion of gold, by distributing the metal along the surface and

controlling the size. The gold load on TiO2 also plays an

important role in the activity; the materials prepared by

D–P shows that 0.5 wt% of gold is the optimum to improve

the photodegradation up to 80%. All the materials with

loads of 1.5% of Au/TiO2 presented a detrimental effect on

the TiO2 photoactivity, so this load of metal is not efficient

for photocatalytical purposes. The Au/TiO2 photocatalysts

should posses gold particles with diameters below 8.6 nm

0.25 0.50 0.75 1.00 1.25 1.500

100

200

300

400

500

600

1/K

0 (m

in)

% Au

TiO2

PD D-P

CD

Fig. 6 Inverse of rate of degradation (1/K0) as a function of the Au

load on the TiO2

5 6 7 8 9 10 11 12 13 14 15

0

100

200

300

400

500

600

1/K

0 (m

in)

Particle size (nm)

Fig. 7 Inverse of rate of degradation (1/K0) of 4-CP as a function of

gold particle size. The continuous line is to guide the eye

Top Catal (2011) 54:519–526 525

123

in order to improve the photoactivity of the commonly used

TiO2.

Acknowledgments This project was partially supported by

PROMEP and CONACyT (Mexico) through grant No. 49482.

S. Oros-Ruiz thanks to CONACyT for the fellowship 213621

Granted.

References

1. Pileni MP (2005) Nanocrystals forming mesoscopic structures.

Wiley, Weinheim, Germany

2. Haruta M (2003) The chemical record 3:75–87

3. Haruta M (2004) Gold Bull 37:27–36

4. Salata OV (2004) J Nanobiotech 2:1–6

5. Alivisatos P (2004) Nat Biotech 22:47–52

6. Jakob M, Levanon H (2003) Nano Lett 3:353–358

7. Thompson D (2003) Appl Catal A: General 243:201–205

8. Sobana N, Muruganadham M, Swaminathan M (2006) J Mol

Catal A: Chem 258:124–132

9. Li XZ, Li FB (2001) Environ Sci Technol 35:2381–2387

10. Tian Y, Tatsuma T (2005) J Am Chem Soc 127:7632–7637

11. Haruta M (1997) Catal Today 36:153–166

12. Dawson A, Kamat PV (2001) J Phys Chem B 105:960–966

13. Narayanan R, El-Sayed M (2005) J Phys Chem B 109:12663–

12676

14. Wood A, Giersig M, Mulvaney P (2001) J Phys Chem B

105:8810–8815

15. Sivalingam G, Nagaveni K, Hedge MS, Madras G (2003) Appl

Catal B: Environ 45:23–38

16. Allmond CE, Oleshko VP, Howe JM, Fitz-Gerald JM (2006)

Appl Phys A 82:675–678

17. Tran H, Scott J, Chiang K, Amal R (2006) J Photochem Photobiol

A: Chem 183:41–52

18. Wang H, Wu Y, Xu BQ (2005) Appl Catal B: Environ

59:143–150

19. Orlov A, Jefferson D, Macleod N, Lambert RM (2004) Catal Lett

92:41–47

20. Rodrıguez-Gonzalez V, Zanella R, del Angel G, Gomez R (2008)

J Mol Catal A: Chem 281:93–98

21. Chan SC, Barteau MA (2005) Langmuir 21:5588–5595

22. Zanella R, Giorgio S, Henry CR, Louis C (2002) J Phys Chem B

106:7634–7642

23. Zheng N, Fan J, Stucky G (2006) J Am Chem Soc 128:6550–

6551

24. Cheng S, Tsai S, Lee Y (1995) Catal Today 26:87–96

25. Mills A, Wang J (1998) J Photochem Photobiol A: Chem

118:53–63

26. Li X, Cubbage JW, Tetzlaff TA, Jenks W (1999) J Org Chem

64:8509–8524

27. Guillard C, Disdier J, Herrmann JM, Lehaut C, Chopin T, Malato

S, Blanco J (1999) Catal Today 54:217–228

28. Bamwenda GR, Tsubota S, Nakamura T, Haruta M (1995) J

Photochem Photobiol A: Chem 89:177–189

29. Zanella R, Louis C (2005) Catal Today 107–108:768–777

30. Braunstein P, Lehner H, Matt D (1990) Inorg Synth 27:218–221

31. Zheng N, Stucky G (2006) J Am Chem Soc 128:14278–14280

32. Porter J, Li Y, Chan C (1999) J Mater Sci 34:1523–1531

33. Kamat PV (2007) J Phys Chem C 111:2834–2860

34. Kamat P (2002) J Phys Chem B 106:7729–7744

35. Guzman C, Del Angel G, Gomez R, Galindo F, Zanella R, Torres

G, Angeles-Chavez C, Fierro JLG (2009) J Nano Res 5:13–23

36. Pelizzetti E, Minero C (1993) Langmuir 9:2995–3001

526 Top Catal (2011) 54:519–526

123