Author's Accepted Manuscript

Production Of Heterostructured Tio2/Wo3 Nanopar-ticulated Photocatalysts Through A Simple One PotMethod

Isabela Alves de Castro, Jéssica Ariane de Oliveira,Elaine Cristina Paris, Tania Regina Giraldi, CaueRibeiro

PII: S0272-8842(14)01734-9DOI: http://dx.doi.org/10.1016/j.ceramint.2014.11.001Reference: CERI9441

To appear in: Ceramics International

Cite this article as: Isabela Alves de Castro, Jéssica Ariane de Oliveira, Elaine CristinaParis, Tania Regina Giraldi, Caue Ribeiro, Production Of Heterostructured Tio2/Wo3Nanoparticulated Photocatalysts Through A Simple One Pot Method, CeramicsInternational, http://dx.doi.org/10.1016/j.ceramint.2014.11.001

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1

PRODUCTION OF HETEROSTRUCTURED TiO2/WO3

NANOPARTICULATED PHOTOCATALYSTS THROUGH A SIMPLE ONE

POT METHOD

Isabela Alves de Castroa, Jéssica Ariane de Oliveirab, Elaine Cristina Parisc, Tania

Regina Giraldib, Caue Ribeiro

c, *

a Universidade Federal de São Carlos, Rod. Washington Luiz, km 235, CEP: 13565-905, São

Carlos, SP, Brazil.

b Universidade Federal de Alfenas, Campus Avançado de Poços de Caldas, Rodovia José

Aurélio Vilela, nº 11.999, CEP: 37715-400, Poços de Caldas, MG, Brazil.

c Embrapa CNPDIA, Rua XV de Novembro, 1452, CEP: 13560-970, São Carlos, SP, Brazil.

*Corresponding author: caue.ribeiro@embrapa.br

Phone: +55 16 2107-2915 / Fax: +55 16 3372-5958

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Abstract

This paper reports a simple one-pot route to synthesize TiO2/WO3 nano-heterostructures

applied as photocatalysts to the degradation of water contaminants. The method was based on

the formation of a polymeric structure from Ti and W complexes that were evenly distributed in

the precursor to avoid phase separation during calcination steps. This strategy was shown to

effectively produce the desired heterostructures, which were well-distributed and possessed

interesting photocatalytic activities when compared with pristine oxides. Characterization of the

heterostructures showed possible doping of each oxide, which may interfere with electronic

properties. Additionally, an increase in surface area was observed according to TiO2

proportions. However, high-resolution electron microscopy confirmed that the heterostructures

were properly obtained, and photoluminescence experiments were well correlated to catalytic

activities. The results indicated higher efficiencies for heterostructures with higher contents of

WO3, although improved activity was observed for the material with 50 wt% of each oxide.

This facile synthesis, and the remarkable properties observed for this heterostructured catalytic

material, confirmed that this route is a candidate for high production, allowing its application in

solving real environmental problems.

Keywords: Calcination processes; (WO3/TiO2) composites; ceramics; photocatalytic activity.

3

Introduction

In recent years, environmental applications of semiconductor nanoparticles have been

extensively studied.[1] The light-induced charge generation in these materials may lead to

oxidizing species and subsequently promote redox reactions, which allow their use in advanced

oxidative processes.[2] Despite TiO2 being the most studied semiconductor in photocatalytic

processes, [3] some drawbacks such as its wide band gap energy – which requires UV light for

excitation – and a relative fast electron-hole recombination still need be addressed.[4,5]

Coupling TiO2 with other semiconductors has been shown to be an effective way to reduce the

recombination rate. [6,7,8] This behavior is attributed to the charge migration between the

interconnected phase, forming a heterostructure or material with distinct crystalline phases in

one particle and sharing at least one surface in a coherent manner [9,10,11,12] In any

heterostructure, because the Fermi levels should be the same at the semiconductor’s interface,

the charge separation (for different phases) will occur when the system is illuminated. This

generally improves the photocatalytic response because the recombination rate is reduced, and

in some cases, the light harvesting is improved due to the generation of other donor levels at the

interface.[12]

Focusing on this strategy, the major tasks are to define which semiconductor is adequate to

be coupled to TiO2 nanoparticles and which synthesis method is most suitable for this purpose.

WO3 is a semiconductor with similar interplanar spaces to TiO2 and a wide bandgap that

depends on its crystalline phase.[13] Previous papers have reported that WO3:TiO2 may also

increase the range of light absorption, which is desirable to improve the photocatalytic

efficiency under solar light. In fact, the differences between these oxides can give a Type I

heterostructure, i.e., a coupled material where the bandgaps are not fully but partially

overlapped.[8,14,15,16]

In determining a suitable synthesis route, a one-pot synthesis is desirable, as it would

provide good homogeneity through the simultaneous crystallization of both materials. On the

other hand, these processes may lead to phase segregation or uncontrollable doping, which

4

implies that detailed synthesis studies are further necessary to propose reliable methods, assure

desirable oxide relations (% weight of each material) and demonstrate the possibility of large

scale production. An adequate method for such goals is the calcination of polymeric precursors

based on poly-carboxyl acid such as citric acid (CA), which can complex metallic ions in

aqueous solutions avoiding hydrolysis. CA complexes can be further reacted against different

alcohols, where ethylene glycol (EG) permits the reaction with two complexes per molecule and

forms a polymeric resin. This polymeric network maintains the homogeneously distributed

cations in a three-dimensional lattice, avoiding precipitation or phase segregation during the

calcination step.[17,18] Because all of the steps can be performed in industrial plants, this

procedure can easily be applied to the large scale production of these materials. However, it is

still necessary to determine the optimum conditions to produce the heterostructure instead of

doped oxides because the high cation homogeneity can favor this process. 19,20

Thus, in this paper, we studied the influence of synthesis variables in TiO2/WO3

heterostructure synthesis by the polymeric precursor method, focusing on the final

photocatalytic property of each system. Our photoactivity results show similar trends compared

with more complex synthetic methods, showing that this simple route may be adequate for the

large production of this heterostructure for environmental applications.

1. Material and methods

2.1. Particle synthesis

The polymeric precursor method consists of chelated metallic ions attached to citric acid

(CA). A metallic citrate is polymerized against ethylene glicol (EG) (High purity – Ecibra). A

solution named polymeric resin is produced by the mixing of titanium citrate and tungsten

citrate before the polymerization step in a range of mass ratios: 10 wt%, 20 wt%, 50 wt%, 80

wt% and 90 wt% of TiO2.

5

To obtain the titanium citrate, CA (99.5% - Synth) was dissolved in deionized water, and

titanium isopropoxyde (97% - Sigma Aldrich) was added to the solution in a 3:1 molar ratio

(CA:Ti). The mixture was stirred for 2 h at 70˚C. Tungsten citrate was obtained by solubilizing

tungstic acid (99% - Sigma Aldrich) in H2O2 (35% - Dinâmica), forming a stable complex. CA

was added in this complex at a 10:1 molar ratio (CA:W). The citrates were mixed in proportions

described below, followed by the addition of EG with a mass ratio of 40:60 EG:CA and stirring

for 1 h at 70˚C. The polymeric resin was annealed at 300°C for 2 h to eliminate organic residues

that remained from the CA and EG. After this first thermal treatment, the powder was annealed

at 500˚C for 2 h to promote crystallization and heterostructure formation. In addition, the

samples with different contents of TiO2 were named m wt% TiO2, m being equal to the TiO2

mass ratio in relation to WO3 mass.

2.2. Characterization

To verify the crystalline structure of the samples, X-ray diffraction (XRD) analyses were

performed on a Shimadzu XRD6000 diffractometer with Cu Kα radiation in 0.15456 nm at 30

kV and 30 mA. The conditions used in these analyses were: scanning at 2θ between 10° and

60°, an exposure time of 1 s and an angular pass of 0.02° in continuous mode. In addition to

XRD analysis, Raman spectroscopy was performed with a FT-Raman Bruker RFS 100/s, using

the 1063 nm line of a YAG laser. Specific surface areas (SA) were determined by nitrogen

physical adsorption at 77 K, using a Micromeritics ASAP 2000 particle size analyzer. The

surface areas were evaluated using the standard BET procedure.

The particles morphologies were characterized by field emission scanning electron

microscopy (FE-SEM, JEOL JSM 6701F). The characterization was done with a 200 kV high

resolution transmission electron microscope (HRTEM) (FEI Tecnai20). TEM samples were

prepared by wetting carbon-coated copper grids with a drop of the aqueous colloidal

suspensions, followed by drying in air. Semi-quantitative atomic composition was evaluated by

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energy-dispersive X-ray (EDX) spectroscopy in an EDX Link Analytical device (Isis System

Series 200) coupled to a LEO 440 SEM microscope.

Photoluminescence spectra (PL) were obtained in a Perkin Elmer luminescence

spectrometer (model LS-50b). The samples were dispersed in water in 0.5 mg L-1 and excited at

254 nm. Emissions of the samples were collected at 90° to the incident beam.

2.3. Photocatalytic activity

Photocatalytic activity toward Rho-B dye oxidation was tested under UVC illumination.

Equivalent catalyst amounts (200 mg L-¹) were exposed to Rho-B solution (5.0 mg L−1)

(Contemporary Chemical Dynamics). The systems were placed in a photo-reactor at a

controlled temperature (20°C) and illuminated by four UVC lamps (TUV Philips, 15 W, at a

maximum intensity at 254 nm). The dye degradation was monitored by measuring UV–Vis

spectra (Shimadzu-UV-1601 PC spectrophotometer, λ=554 nm)[21] in different periods of light

exposure. To test the direct UV-photolysis of the dye, reference experiments were performed in

a Rho-B solution without any catalyst, showing also negligible degradation by this mechanism.

Rho-B was chosen because its degradation depends only on the photocatalyst parameters[22].

As a reference, the photocatalytic behavior of isolated TiO2 nanoparticles obtained in this

research was evaluated. Additionally, to verify the heterostructure formation, the physical

mixtures (PM) of isolated oxides at 50 wt% of TiO2 and WO3, named as PM-50 wt%, were

added into the Rho-B solution and exposed to UV radiation.

2. Results and Discussion

Figure 1 shows the XRD patterns of the as-synthesized samples. TiO2 diffracted peaks

could be indexed by means of the Joint Committee on Powder Diffraction Standards to a

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mixture of anatase (A) as a majority phase (JPDS card no: 01-089-4921) and rutile (R) (JPDS

card nº: 03-065-0192). All of the diffraction peaks of synthesized WO3 can be indexed to the

monoclinic phase (JPDS: 043-1035). For the heterostructures, a mixture of both TiO2 and WO3

crystalline phases were obtained from the 10 wt% to 50 wt% TiO2. After the 80 wt% TiO2, any

WO3 peaks were not observed, indicating the possible W doping in TiO2. It is important to

notice that identification of WO3 peaks is possible in the physical mixture of isolated powders in

the 95wt% TiO2 as shown in Supplementary Figure 1, confirming that this is not a matter of

WO3 content. Displacements were observed for anatase peaks in the 90 wt% and 80 wt% TiO2

samples (Figure 1b, at 1 region), which suggests W doping in these samples. Another observed

feature was the peak broadening, mainly for anatase peaks, at 2ϴ = 25.34º, 37.76º, 48.16º,

53.99º, 55.11º and 62.82º, as well as the suppression in the rutile peaks. Regarding the 10 wt%

and 20 wt% TiO2 samples, the relative intensity of the (200) and (220) WO3 planes were

remarkably decreased when compared with the reference WO3. This finding suggests

morphological changes in the presence of TiO2, as shown in the expanded view of Figure 1c,

region 2.

Raman spectra were obtained to confirm the WO3 and TiO2 formation (Figure 2). All

vibration modes of TiO2 spectrum can be related to the anatase phase, with characteristic

vibration modes at 144, 394, 506 and 630 cm-1. [23] The lattice vibrations between 70-100 and

approximately 267, 327, 708, 802 cm-1 are features of the monoclinic WO3 phase.[24] For

intermediate contents such as the 50 wt% and 80 wt% TiO2 samples, the heterostructure

formation is evidenced by the presence of typical shifts related to both TiO2 and WO3. However,

similarly to the XRD pattern, no WO3 vibration mode was observed for the 90 wt% TiO2,

confirming that in low amounts the synthesis method tends to form doped TiO2 instead of

heterostructures. A clear displacement in the 144 cm-1 TiO2 peak was observed in the

heterostructured samples, from 20 wt% to 90 wt% TiO2, which is also in agreement with XRD

data. This shows that the doping occurs even in conditions where W content exceeds the limit of

solid solution, i.e., W6+ may be introduced into the TiO2 lattice and replaces Ti4+ ions for W6+. A

8

detailed analysis shows that this is possible because the ionic radio of both cations is similar

(0.065 nm and 0.0600 nm, respectively).[25] Displacements of WO3 vibration modes in the 10

wt% and 20 wt% TiO2 samples were also observed at 80 cm-1 and 266 cm-1 monoclinic peaks,

which shows that the inverse (Ti doping in WO3 structure) is also possible.

The interaction between the oxides is also revealed by specific surface area

measurements, as shown in Table 1. The surface area obtained for the reference TiO2 was 87

m²g-1, consistent with anatase surface area measurements obtained by the same procedure as

reported in a recent work.3 On the other hand, the WO3 surface area was below the other

samples. This result may be related to the hydrated agglomerates after synthesis, which would

reduce its available surface, and this characteristic has been already observed in previous

papers.[26] For the heterostructures, the S.A. increases as the TiO2 contents increase; for

example, a high surface area was obtained for the 50 wt% TiO2. It is noticeable that the surface

areas obtained cannot be correlated by the average of isolated powder surface areas, i.e., a

synergistic effect occurs during the synthesis and results in higher area measurements. For

example, in the 50 wt% TiO2 sample, an average surface area would mean 44.6 m2 g-1. Then, the

measured S.A. value (107.6 m2 g-1) shows that during the calcination process, the phase

segregation improved the effective surface area.

The sample’s morphologies were verified by SEM according to Figure 3. In Figure 3a,

agglomerates of TiO2 nanoparticles were observed, leading to large clusters. In Figures 3b to f,

one may identify TiO2-coated WO3 clusters following the coverage degree according to TiO2

content. TiO2 coverage over WO3 was verified for the heterostructured samples. In fact, the

agglomerates observed in the heterostructures were related to WO3 particles with micrometric

sizes, and this was verified by EDS analysis of the 20 wt% TiO2 (Figure 4) where agglomerates

revealed W intensities (region 1) higher than what was observed for Ti (region 2).

It is important to mention that the 50 wt% TiO2 sample (Figure 3d) showed

homogeneous distribution of TiO2 nanoparticles, which is consistent with the high S.A.

measured and provides a good TiO2 distribution over WO3 particles. The lower surface area

9

observed for the WO3 particles (Table 1) may be related to the morphology observed in Figure

3g, showing high agglomeration. This finding is very important because the co-synthesis with

TiO2 induced a change in WO3 morphology, probably due the phase separation during the

calcination step and its preferential growth in given directions. In fact, this behavior was

reported in a recent paper, where TiO2 played an important role in WO3 architecture. The

structure size was dependent of the temperature during the calcination step and of the TiO2

contents. [27]

HRTEM images for the 20 wt%, 50 wt% and 80 wt% TiO2 samples are shown in Figure

5. In Figure 5a, the cluster formation for 20 wt% TiO2 sample was confirmed, as observed by

SEM images. On the inset (Figure 5b), the particle size range was determined from 15 to 47 nm,

which is related to the TiO2 nanoparticles because the smaller particles were identified as this

oxide. The heterostructure formation was confirmed in the 50 wt% TiO2 by lattice parameters

approximately 0.27 and 0.24 nm, which is in good agreement with the monoclinic WO3 (022)

and anatase TiO2 (004) crystallographic planes, respectively (Figure 5c). At Figure 5d,

corresponding to the 80 wt% TiO2 sample, selected area electron diffraction (SAED) was used

to verify the crystallinity. The presence of diffraction rings, as shown, is typical of

polycrystalline samples. The first ring is indexed as the (200) plane relative to the WO3

monoclinic phase. The other rings were indexed as (103), (200) and (105) planes of anatase

TiO2. This result, contrasting to the XRD and Raman data, shows that even in smaller contents

the phase segregation took place, showing the presence of heterostructures. However, the

comparison with previous results shows that the final heterostructures are probably formed by

W-doped TiO2 and WO3. The EDS analysis for this sample confirms the presence of both

elements, as shown in the Figure 6, and helps in SAED identification.

The photocatalytic activity of the samples was evaluated by using Rho-B degradation as

a model reaction. According to Figure 7, one can observe negligible dye degradation without a

catalyst, confirming the Rho-B stability under UV light. For all of the catalyzed samples, due to

the exponential profiles observed for the kinetic degradation of Rho-B under UV light, one can

10

suggest that the reaction is first-order with respect to the dye.[28,21,2] A simple kinetic model

for this reaction can be proposed as follows:

ϴ = – d [Rho-B] / dt = k [Rho-B] [OH.] (1)

where ϴ is the reaction rate, k is the rate constant, [Rho-B] is the dye concentration and [OH.] is

the free radical concentration formed by the photocatalyst. Due to the radical formation, it is

assumed to be a steady-state reaction and to be proportional to the amount of active sites in the

photocatalyst, and it is assumed to be constant and proportional to its surface area, i.e., [OH.] =

k*.[A.S]. Therefore, we assume that the rate constant k’ = k. k*.[A.S.] and approximate this

behavior to fit a pseudo-first order reaction model, as follows:

ϴ = – d [Rho-B]/dt = k’ [Rho-B] (2)

The k’ values for the samples are shown in Table 2. All of the heterostructures

showed better photoactivities compared with the isolated oxides. It is important to notice that

this catalytic effect is associated to the heterostructure formation because comparison with the

degradation profile demonstrated by a physical mixture of unreacted powders, named PM-50

wt% (in the proportion of 50 wt%, corresponding to the best results observed for the

heterostructured samples) showed a remarkable difference with the 50 wt% TiO2

heterostructure. For example, the degradation constants (k’) obtained were 2.66 and 31.05 (10-

3/min), respectively. However, all of the heterostructured samples showed good final

degradation values after 180 min, i.e., below 5% of residue. These differences may be correlated

to the surface areas, as one can see in Figure 8, where S.A. and the degradation constants (k’) of

the samples were plotted against the wt% of TiO2. The samples with high surface area showed

higher photoactivities, especially for the 50 wt% TiO2 sample. In fact, the surface area can

influence the total number of active sites and consequently in the Rho-B degradation. However,

11

one can notice that the heterostructures with higher TiO2 amounts were less effective than the

others, showing that the best conditions were attained in WO3 proportions higher than 50 wt%.

Additionally, the result from the 50 wt% TiO2 sample is very remarkable, suggesting that this

condition is ideal for the production of this material through this route.

To gain a better understanding of the photocatalytic behavior, PL spectra of the

samples were taken because photoeffects are dependent on the nanoparticles electronic features.

Possible photocatalytic changes can be related to its different donor-acceptor levels. The PL

spectra were obtained by exciting the samples at 254 nm because this wavelength is the same

used in photocatalytic tests under UV light. As shown in Figure 9, the 50 wt% TiO2 presents a

more enhanced PL peak at the expected position for WO3, indicating that the efficiency of the

band decay process for this oxide was improved. This finding also suggests that this oxide is an

active part of the photocatalytic oxidation process because its high PL spectra shows that TiO2

are modifying WO3 electronic features better than WO3 is modifying TiO2. This result is

probably correlated to the high photocatalytic activity observed for this sample. A shift in the

maximum absorption peak was also verified to the heterostructures, as seen at the Table 3,

which is probably due to the absorption product of isolated WO3 and TiO2 oxides.

3. Conclusions

Here, a one-pot method to produce heterostructured WO3/TiO2 catalysts that is simple and

capable of being extended to higher production yields was presented and discussed. The method

allowed the production of different oxide relationships by spontaneous phase separation during

the calcination step of a polymeric precursor, produced by citrate complexes of each cation. The

heterostructure formation was confirmed by XRD, Raman spectroscopy and HRTEM images,

and the photocatalytical essays showed that it is possible to obtain very active materials with

high surfaces areas. These results can support studies about facile methods to improve the

12

production of photocatalytic materials, which is needed for real applications with environmental

purposes.

Acknowledgments

We acknowledge the financial support from FAPESP (2011/07484-8 and 2011/21566-7),

CNPq, CAPES, FINEP and Embrapa. We also gratefully acknowledge the HRTEM facility at

LCE/DEMa/UFSCar São Carlos - Brazil and LIEC/UFSCAR São Carlos - Brazil for providing

Raman and PL facilities.

Supplementary Information

Electronic Supplementary Information (ESI) available: XRD data of 95wt% TiO2 physical

mixture.

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Figure captions

10 20 30 40 50 60 70 80

2 region

20wt%

80wt%

50wt%

Inte

nsity/ a

.u.

2θ/degree

222

122

220

202

022

112

120

200020

WO3

10wt%

002

90wt%

TiO2

RRA A

AAA

AAAA

RR

AAA

AA: anatase

R: rutile

1 region

(a)

18

25 30 35 40 45 50

R RR A

A

A

A

90wt%

Inte

nsity/ a

.u.

2θ/degree

80wt%

TiO2

A

1 region

24 32 40

2 region

20wt%

Inte

nsity/ a

.u.

2θ/degree

22

2

12

2

22

02

02

02

2

11

2

12

0

20

00

20

WO3

10wt%

00

2

(b) (c)

Figure 1. XRD patterns of the synthesized samples (a); expanded view of selected areas in 1

region (b) and 2 region (c).

100 200 300 400 500 600 700 800 900 1000

630506 394

802

708

327

266 129 80

64

Norm

aliz

ed

Inte

nsity

Raman shift (cm-1)

WO3

10wt%

20wt%

50wt%

80wt%

90wt%

TiO2

144

Figure 2. Raman spectra of the samples.

19

Figure 3. SEM images: (a) TiO2, (b) 90 wt%, (c) 80 wt%, (d) 50 wt%, (e) 20 wt%, (f) 10 wt% of

TiO2 and (g) WO3.

(g)

(d)

(a) (b)

(c)

(e) (f)TiO2

WO3

(e)

0 2 4 6

0

2000

4000

6000

8000

10000

Conte

nts

keV

Ti

Cu

W

WO

PW Ti

1 region

Figure 4. EDS analysis for 20 wt% TiO

spectrum for region 1; (b) EDS sp

(a)

8 10

WCu W

0 2 4 6 8

0

2000

4000

6000

8000

Co

nte

nts

KeV

Ti

O

Cu

W

W

PW

Ti

Ti CuW

W

2 region

(b) (c)

wt% TiO2 sample: SEM image of the analyzed region (a); EDS

spectrum for region 1; (b) EDS spectrum for region 2 (c).

20

10

W

(b) (c)

sample: SEM image of the analyzed region (a); EDS

21

Figure 5. HRTEM images of 20 wt% (a-b), 50 wt% (c) and 80 wt% of TiO2 heterostructure (d).

At the inset, selected area electron diffraction (SAED) (d).

(a)

(b)

(c)(c) (d)

22

0 2000 4000 6000 8000 10000

0

2000

4000

6000

8000

Energy/keV

co

un

ts

C

O Ti

Cu

Cu

WCu

Figure 6. EDS for 80 wt% TiO2 sample, analyzed at region 1 (red dot) in Figure 5 (d). Cu

detection refers to the grid used to support the sample.

23

0 20 40 60 80 100 120 140 160 180 200 220 240

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

C/C

0

Time/min

Rho-B

TiO2

WO3

10wt%

20wt%

50wt%

80wt%

90wt%

M-50wt%

Figure 7. Rhod B photocatalytic degradation under UV light, catalyzed by different samples. M-50 wt%

refers to an unreacted oxide mixture (simple mechanical mixture), with 50 wt% of TiO2 and WO3.

24

0 10 20 30 40 50 60 70 80 90 100 110

20

40

60

80

100

120

wt% TiO2

Sp

ecific

Su

rfa

ce A

rea

/ (m

2g

-1)

5

10

15

20

25

30

35

k'/ (1

0-3. m

in-1)

Figure 8. Plot of the wt% TiO2 in the heterostructures against the Specific Surface Area and the

degradation constant (k’).

25

300 320 340 360 380 400 420 440 460 480

0.0

0.2

0.4

0.6

0.8

1.0

Norm

aliz

ed Inte

nsity

λ/nm

50wt%

20wt%

WO3

90wt%

TiO2

80wt%

10wt%

Figure 9. PL spectra of the samples. All the intensities were normalized by the most intense

spectrum (50 wt% TiO2).

26

Tables

Table 1: Specific surface area (S.A.) of the samples, determined by BET method.

Sample S.A.(m² g-1

)

TiO2 87 90 wt% TiO2 68.2 80 wt% TiO2 97.4 50 wt% TiO2 107.6 20 wt% TiO2 37.1 10 wt% TiO2 24.3

WO3 2.2

Table 2. First-order kinetic constants for Rho-B degradation under UV light (k’).

Sample k’ /(min-1

) x 103 ± error limit x 10

3

TiO2 7,24 ± 0,104 90 wt% TiO2 17,62 ± 0,792 80 wt% TiO2 20,71 ± 0,775 50 wt% TiO2 31,05 ± 6,67 20 wt% TiO2 19,74 ± 0,487 10 wt% TiO2 19,57 ± 0,721

WO3 1,52 ± 0,061 M-50 wt% 2,66 ± 0,036

Table 3. PL intensities and the maximum emission of the samples, compared with the most

intense spectrum.

Sample λ (nm) Intensity(%)

TiO2 369.99 23 90 wt% TiO2 371.01 25 80 wt% TiO2 368.99 20 50 wt% TiO2 366.65 100 20 wt% TiO2 367.33 70 10 wt% TiO2 369.05 15

WO3 366.84 60