a07v32n2.pdf


41

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Adsorption of hidrogen peroxide on the surface of silica – titania
mixed oxide obtained by the sol-gel processing method

J. E. Gonçalvesa*, U.P. R.Filhob, D.W. Francob and Y. Gushikemc

aCentro Universitário de Ensino Superior, CESUMAR,  Av Guedner 1610, 87050-390  , Maringá, PR, Brazil, e-
bInstituto de Química de São Carlos, USP, São Carlos, SP, Brazil

cInstituto de Química, UNICAMP, CP 6154, 13084-862 Campinas, SP, Brazil
a*mail-jegoncal@cesumar.br

Abstract: This work describes the sol-gel mixed oxide SiO
2
/TiO

2
 property, ST, as prepared, and submitted

to heat treatment a 773 K, STC. SEM and EDS images show, within magnification used, a uniform

distribution of the TiO
2
 particles in SiO

2
/TiO

2
 matrix. Both, ST and STC adsorb hydrogen peroxide on the

surface and through EPR and UV-Vis diffuse reflectance spectra, it was possible to conclude that the

species on the surface is the peroxide molecule attached to the Lewis acid site of titanium particle

surface, α Ti(H
2
O

2
)+. As the material is very porous, presumably the hydrogen peroxide molecule is

confined in the matrix pores on the surface, a reason why the adsorbed species presents an exceptional

long lived stability.

Keywords: sol-gel; silica-titania; hydrogen peroxide adsorption; porous material.

Introduction

The sol-gel process can be described as

a very convenient method to prepare binary oxides

such as SiO
2
/M

x
O

y
, with high purity and

homogeneity [1-6]. Among these, SiO
2
/TiO

2
 having

high concentration of titanium (IV) homogeneously

dispersed in the matrix can be obtained by this

process [7].  The metal oxide incorporated in the

matrix is coordinatively unsaturated and

furthermore can react with other compounds,

resulting in an immobilized solid system [8].  As an

example, the reactive α TiOH groups on the SiO
2
/

TiO
2
 surface can react with hydrogen peroxide,

resulting in the solid SiO
2
/TiO

2
/H

2
O

2
 where the

hydrogen peroxide group is adsorbed.

Several works dealing with the interaction

of H
2
O

2
 with TiO

2
 have been reported, emphasizing

the importance of the mechanism of this reaction

in biochemical and chemical processes [9-10]. The

structure of the adsorbed species has also been

investigated, but the mechanism of the radical

formation is still not well understood [11-14].

Hydrogen peroxide chemisorbed on

titanium dioxide, hereafter named peroxide-modified

titanium dioxide, is investigated as a chemical

analog to the putative soil oxidants responsible

for the chemical reactivity [15].

Supported oxide catalysts containing

transition metal ions are known to be widely used

in oxidation of organic substances with molecular

oxygen. Therefore at seems interesting to study

the state of the oxygen absorbed on their surface

[16-19].

The EPR measurements [12, 19-20] have

shown that the oxygen adsorption on n-semi-

conducting oxides and radiation chemisorptions

on dielectrics results in formation of the O
2

-

adsorbed radicals. This technique has been widely

used for the studies of supported oxide catalysts.

It has also been shown that metallic

titanium and hydrogen peroxide interacts strongly

and that a titanium-peroxide gel with pH around 4

are formed, then has been showed that hydrogen

peroxide decomposed [21-22].

The presence of such radicals may be of

considerable importance in many research areas,

such as photochemistry, solar energy conversion

Ecl. Quím., São Paulo, 32(2): 41-45, 2007

Volume 32, número 2, 2007



42

[9, 23-25], and the biochemistry of respiration and

inflammation [10-11].

This work reports the interaction of

hydrogen peroxide (H
2
O

2
) on the surface of silica-

titania (SiO
2
/TiO-

2
) mixed oxide obtained by the

sol-gel processing method. Studies have shown

that H
2
-O

2
 would form stable peroxide radicals

adduct with SiO
2
/TiO-

2
. In this study, adsorption

of H
2
O

2
 by SiO

2
/TiO-

2
 from aqueous solutions is

investigated as well as the formation of peroxide

radicals by Electron Paramagnetic Resonance

(EPR) and visible-UV spectrometry using a diffuse

reflectance technique.

Experimental details

Preparations

SiO
2
/TiO

2
 mixed oxide was prepared by

the sol-gel processing method as described

elsewhere [26], (1) 12.1 mL of 0.85 mol.L-1 HNO
3

aqueous solution were added to 250 mL of 50% (v/

v) tetraethoxysilane (TEOS)/ethanol solution, and

the mixture was stirred at 353 K for 2.5 h. (2) About

34 mL of titanium (IV) butoxyde (TBO) and 490 ml

of ethanol were then added and the mixture was

stirred for 2 h at room temperature. (3) 66 ml of 0.6

mol.L-1 HNO
3
 solution were slowly added and

allowed to rest for gelation. The formed xerogels

were ground, dried at 383 K for 24 h and sieved in

order to obtain particles size between 75 and 250

mm.

Parts of SiO
2
/TiO

2
samples were calcined

at 773 K under air flux. The untreated and heat-

treated silica-titania samples were designated as

ST and STC, respectively. The solid was analyzed

by using the X-ray fluorescence technique on a

Tracor Northern X-ray fluorimeter.

Adsorption of the hydrogen peroxide on SiO
2
/TiO

2

About 10 g SiO
2
/TiO

2
 (calcined, STC and

uncalcined, ST) samples were shaken for 30 min

with 100 mL of 0.5 mol.L-1 hydrogen peroxide

solution. The solutions were decanted and the

hydrogen peroxide determined by iodometric

titration in the solution phase. The solid was

submitted to high vacuum for 30 min at 298 K.

Uv-VIS Spectroscopy

Uv-Vis electronic spectrum of the

materials SiO
2
/TiO

2
 and SiO

2
/TiO

2
/H

2
O

2
 they were

obtained by diffuse reflectance technique. The

spectra were obtained in the region between  200

and 800 nm,  at ambient temperature, using a UV-

Vis-NIR Variam Cary 5G spectrophotometer

connected to a diffuse reflectance accessory using

BaSO
4
  as reference.

Electron Paramagnetic Resonance

The spectra were been obtained in a X-

band frequencies on a Bruker ESP 300E

spectrometer, operating in X band (9.77 GHz). Room

temperature measurements were obtained with

frequency modulation of 100 kHz and amplitude

modulation of 15.7 G. The measures had been

obtained in the temperature of liquid nitrogen with

microwave frequency of 9.46GHz and microwave

power of 2 x 10-1 mW. The field sweep width was

798 G with acquisition time of 671 s. The g value is

referenced to the one of DPPH.

Results and Discussion

Table 1 shows the results of the titanium

analyses in the binary oxide, ST and STC, the

results on specific surface areas and average pores

volume. For the mixed oxide SiO
2
/TiO

2
, designated

as ST, the measurements were made as prepared

and, for mixed oxide designated as STC, the

measurements were made after heat treatment at

773 K.

Table 1: Chemical titanium analysis in oxides binary,

Specific Superficial Area, S
BET

, and average volume of the

pores, Vp.

The results of specific surface area S
BET

 (Table 1)

show that  for STC a reduction of the area after is

observed under thermal treatment as consequence

of pores collapse [26-28]. However, the observed

area decrease is very small indicating that TiO
2

particles inside the SiO
2
 matrix is thermally few

mobile upon treatment at this temperature. As

consequence, the average pore volume remains

practically the same after the heat treatment.

The materials submitted to the scanning

electron microscopy  ST and STC have shown that

the titanium is distributed uniformly on the material,

Ecl. Quím., São Paulo, 32(2): 41-45, 2007



43

as can be observed by Figure 1. The thermal

treatment of STC (calcination at 773 K under air

flow) did not modify the uniform distribution of

titanium oxide particles in the material. Within the

magnification used, this fact demonstrates that not

formation of any islands in the mixed oxide [26].

Analysis by X-ray diffraction have shown that the

materials are amorphous and thermally very stable

[26].

Figure 1: (a) Scanning electron micrographs of ST and (b)

the corresponding EDS  image for Ti atoms.

(a)

Electron paramagnetic resonance

spectrum for STC/H
2
O

2
 (Figure 3),  shows three

values for g: 2.00, 2.01 and 2.03. These values are

assigned to  superoxide species on the matrix

surface [34].

Figure 3: EPR spectrum of the material STC/H
2
O

2
. The

data were obtained at    77 K.

Ecl. Quím., São Paulo, 32(2): 41-45, 2007

(b)

In solutions of low pH surface Ti(IV)

reacts with H
2
O

2
 with the formation of a complex of

yellow coloration (reaction 1). This property has

been used as procedure of analytical chemistry to

determine this metallic ion [29-30]. In this case after

the immersion of binary oxides ST and STC in a

H
2
O

2
 solution, the solid became yellow due to the

formation of the complex on the surface of the

material.

The reaction that occurs on the surface can be

represented by the following equation:

α Τι(ΟΗ) + Η+   +  Η2Ο2  →  α Τι(Η2Ο2)
+   +    Η2Ο (1)

where α Ti(OH) is the hydroxyl group attached to

titanium on the surface of the matrix and α Ti(H
2
O

2
)+

represents the complex titanium-peroxide formed

on the surface of binary oxide.

The UV-vis spectrophotometry was used

to check the formation of the hydrogen peroxide

complex on the matrix. Figure 2 shows the electronic

spectra ST and ST/H
2
O

2
. It shows the LM charge

transfer oxygen to the metal, for ST, at 352 nm.

After treatment and adsorption of peroxide on the

surface, LM is observed at 400 nm for ST/H
2
O

2
, a

clear indication that on the surface the titanol group

(α Ti(OH)), was replace by hydrogen peroxide

moleculeα Ti(H
2
O

2
)+[31-33].

Figure 2: Uv-Vis electronic spectrum of diffuse reflectance

of  ST and ST(H
2
O

2
).



Stability of adsorbed peroxide

Stability of adsorbed peroxide on ST and STC, was

tested for ST/H
2
O

2
 and STC/H

2
O

2
 heated at 333 K.

In this case, for both materials, an approximate 5

wt% reduction of peroxide adsorbed was detected.

After longer time allowed to rest at room

temperature, about nine months, a loss of 50 wt%

of hydrogen peroxide was observed. A complete

and fast decomposition of peroxide is observed

when the samples, ST(H
2
O

2
) and STC(H

2
O

2
), are

heated at 373 K  for 45 min. This experiment shows

how the peroxide molecule adsorbed in the pores

of ST and STC matrices are stabilized.

Regeneration of the matrix

As the ST and STC is a matrix where the

silica framework confers an exceptional mechanical

and chemical stability to the TiO
2
 particles, linked

to matrix by Si-O-Ti bond, after treatment with

hydrogen peroxide it is not leached to the solution

phase. A complete regeneration of the matrix is

possible heating the sample at 373 K during 45 min

for a complete regeneration of the matrices

ST(H
2
O

2
) and STC(H

2
O

2
) and prompt to be reused.

Conclusions

The mixed oxide SiO
2
/TiO

2
, prepared by

the sol-gel processing method, as prepared (ST)

and submitted to heat treatment (STC) showed that

the matrix obtained is very resistant under

Ecl. Quím., São Paulo, 32(2): 41-45, 2007

The effectiveness in adsorbing H
2
O

2
 by

the material as prepared, ST, and submitted to

calcination, STC, for a fixed concentration of

peroxide and using nearly the same mass of ST or

STC, was tested by determining the amount of H
2
O

2

adsorbed at various pH. Figure 5 shows that for

both matrices, at various solutions pH, the

adsorption capacities determined are nearly the

same.  The maximum adsorption occurred at pH

between 3 and 4. A supposition that Lewis acid

sites are the reactive centers and they are generate

at lower pH by the reaction is clearly supported by

this experiment [31]. The reaction which occurs

can be represented by the reaction 2:

≡TiOH + H+ → ≡Ti+ + H
2
O           (2)

When pH is much lower, i.e.

below 3, it is presumed that an increase of anionic

counter ion of the acid, used to adjust the solution

pH, compete with peroxide at the solid-solution

interface or, peroxide molecules are protonated at

this pH, decreasing the amount of this species on

the surface.

Figure 5: Isotherm of adsorption of hydrogen peroxide

on ST and STC at various solutions pH.  [H
2
O

2
] = 1 x 10-

2 mol.l-1, mass of 0.1 g for ST and STC used and temperature

of 298 K.

44

Isotherm of adsorption

 In order to determine the matrix

adsorption capacity of hydrogen peroxide, the

isotherm of adsorption at 298 K was determined.

Figure 4 shows the isotherms obtained for STC for

solid immersed in a solution containing the solid

at pH 3.  Saturation of the STC surface by H-
2
O

2
 is

achieved for surface concentration of peroxide of

0.9 mmol.g-1 at pH 4. This adsorption of hydrogen

peroxide on the surface may occurs exclusively on

the Lewis acid sites.

Figure 4: Isotherm of adsorption of hydrogen peroxide

on STC matrix at 298 K and pH 3.



45

mechanically and chemically point of view. The

low thermal mobility of TiO
2
 particles and the

resistance of silica framework, resulted only in a

small S
BET 

decrease of STC in comparison with ST.

 The scanning electronic microscopy showed that

the titanium is uniformly distributed throughout

the matrix.

The exceptional stability of H
2
O

2
, presumably

confined in the pores of the matrix surface, as

a•Ti(H
2
O

2
)+ species, under application point of

view, represents as a new and attractive material

useful as powerful oxidant in a chemical reaction

under dynamical flow condition.

Acknowledgements

Authors acknowledge FAPESP for

financial support and JEG is indebted to CNPq for

fellowship.

Received 16 March 2007

Accepted 22 May 2007

References
[1] R. J. P. Corriu and D. Leclercq, Angew. Chem. Int.
(Ed. Engl), 35 (1996) 1420.
[2]  L. L. Hench and J. K. West, Chem. Rev., 90 (1990)
33.
[3]  Z. Liu; J. Tabora and R. J. Davis, J. Catal., 149
(1994) 117.
[4] R. M. Almeida and E. E. Christensen, J. Sol-Gel Sci.
and Technol., 8 (1997) 409.
[5]  J. B. Miller, L. J. Mathers and  E. I. Ko, J. Mater.
Chem., 5 (1995) 1759.
[6] M. A. Cauqui, J. J. Caluino, G. Cifredo, L. Esquivias
and J. M. Rodríguez-Izquierdo, J. Non-Cryst. Solids,
147-148 (1992) 758.
[7] A. Clearfield, Inorganic Ion Exchange Materials, CRC
Press Inc., Boca Raton, FL, 1982.
[8]  S. Denofre, Y. Gushikem and C. U Davanzo, Eur. J.
Solid State Inorg. Chem., 28 (1991) 1295.
[9]  P. Tengvall, L. Bertilsson, B. Liedeberg, H. Ewing
and I. Lundstrom, J. Colloid Interface Sci., 139 (1990)
575.
[10]  G. N. Komratov, I. D. Chausskaya and L. V.
Kustova, Inorg. Mat., 28 (1992) 597.
[11]  D. Schwarzenbach, Inorg. Chem., 11 (1970) 2391.
[12]  J. R. Katzer, G. C. A. Schuit and J. H. C. Van
Hooff, J. Cat., 59 (1979) 278.
[13]  K. Takamura and B. Ranby, J. Phys. Chem., 72
(1968) 164.
[14]  M. Iwamoto and J. H. Lunsford, Chem. Phys.
Lett., 66 (1979) 48.

[15]  M. Ulmann, N. R. de Tacconi and J. Augustynski,
J. Phys. Chem., 90 (1986) 6523.
[16]  C. Guizard, A. Larbot, S. Peres and J. Rouviere, J.
Chim. Phys., 87 (1990) 1901.
[17]  J. F. Quinson, N. Tchipkam, J. Dumas, C. Bovier,
J. Serugheti, C. Guizard, A. Larbot and L. Cot, J. Non-
Cryst. Solids, 99 (1988) 151.
[18]  J. F. Quinson, M. Chatelut, C. Guizard, A. Larbot
and L. Cot., J. Non-Cryst. Solids, 121 (1990) 72.
[19]  V. A. Shvets and V. B. Kazansky, J. Cat., 25 (1972)
123.
[20]  A. H. Boonstra and C. A. H. A. Mutsaers, J. Phys.
Chem., 79 (1975) 1940.
[21]  P. Tengvall, L. Bertilsson, B. Liedberg, H. Elwing
and I. Lundstrom, J. Coll. Int. Sci., 139 (1990) 575.
[22]  P. Tengvall, H. Elwing and I. Lundstrom, J. Coll.
Int. Sci., 130 (1989) 405.
[23]  L. T. Kubota, Y. Gushikem, S. C. De Castro and J.
C. Moreira, Coloids Surf., 57 (1991) 11.
[24]  L. T. Kubota, Y. Gushikem and J. C. Moreira,
Analyst, 116 (1991) 281.
[25]  E. S. Boichinova and T. P. Tsaikov, J. Appl. Chem
URSS, 55 (1982) 46.
[26]  J. E. Gonçalves, Y. Gushikem and S. C. de Castro,
J. Non-Cryst. Solids, 260 (1999) 125.
[27]  A. A. S. Alfaya, Y. Gushikem and S. C. de Castro,
Chem. Mater, 10 (1998) 909.
[28]  M. Schneider and A. Baiker, J. Mater. Chem., 2
(1992) 587.
[29]  Y. M. Gershenzon, S. G. Zvenigonodski and V. B.
Rozenshtein, Russ. Chem. Rev., 59 (1990) 928.
[30]  L. T. Kubota, Y. Gushikem, A. M. Manzanares
and H. Vargas, J. Colloid Interface Sci., 173 (1995) 372.
[31]  P. Tengvall, B. Walevaara, J. Westerling and I.
Lundstron, J. Colloid Interface Sci., 143 (1991) 589.
[32] J. Muhlebach, K. Muller and G. Schwarzenbach,
Inorg. Chem., 11 (1970) 2381
[33]  V. A. Shvets and V. B. Kazansky, J. Catal., 25
(1972) 123.
[34]  R. Konaka, E. Kasahara, W. C. Dunlap, Y.
Yamamoto K. C. Chien and M. Inoue, Free Radical

Biology & Medicine, 27 (1999) 294.

Ecl. Quím., São Paulo, 32(2): 41-45, 2007