the Room-Temperature Phosphorescence
H2O2 Sensor Based on the Room-Temperature Phosphorescence of Nano TiO2/SiO2 CompositeXiaohong Shu,† Ying Chen,† Hongyan Yuan,‡ Shangfeng Gao,‡ and Dan Xiao*,†,‡
College of Chemistry and College of Chemical Engineering, Sichuan University, Chengdu, 610065 P.R.China
A TiO2/SiO2 composite prepared by the sol-gel route can
produce highly emissive broadband room-temperature
phosphorescence at an excitation wavelength of 403 nm.
The white phosphorescence of TiO2/SiO2 could be
quenched by H2O2. The phosphorescence quenching
effect demonstrated excellent sensitivity and high selectivity
to H2O2. Furthermore, the phosphorescence of TiO2/
SiO2 can be recovered when it is dipped in a hydroxylamine
hydrochloride solution. Therefore, the TiO2/SiO2
was used to develop a reproducible phosphorescence
sensor for H2O2. It has been successfully applied to the
determination of H2O2 in the enzymatic catalytic reaction
and real samples.
Phosphors are important materials of considerable interest in
many fields including fluorescent lighting, displays, and X-ray
scintillation. Green et al.1 reported highly emissive broad and
phosphors that can be synthesized from a tetraalkoxysilane solgel
precursor and a variety of organic carboxylic acids. Here, we
report a TiO2/SiO2 composite oxide white phosphor via a solgel
route. It produces highly emissive broadband phosphorescence
from 450 to 650 nm at an excitation wavelength of 403 nm.
The material could be used for the determination of trace
hydrogen peroxide.
Hydrogen peroxide can be harmful to biological systems and
appears to be involved in the neuropathology of central nervous
system diseases.2 Hydrogen peroxide is an important trace gas
that plays a significant role in the troposphere. In addition, H2O2
has an indirect impact on the acid rain procedure that is harmful
to the atmosphere.3 Because the determination of H2O2 is also
very important in enzymatic reactions,4 the trace determination
of H2O2 is of considerable importance in clinical and environmental
applications.
For the determination of H2O2, methods such as titrimetric,5
spectrophotometric,6-8 fluorescence,9-11 electrochemical,12 and
chromatographic13-16 are usually used. The titrimetric detection
method uses simple apparatus but it is less sensitive. The
spectrophotometric methods have to react with a chromogenic
hydrogen donor in the presence of peroxides such as Eriochrome
Black T,6 a mixture of titanium(IV) and 2-((5-bromopyridyl)azo)-
5-(N-propyl-N-sulfopropylamino)phenol,7 oxoperoxopyridine-2,6-
dicarboxylic acid, and vanadate(V).8 The fluorescence methods
involve the fluorescence reaction between fluorescein hydrazide
and hydrogen peroxide,9 the oxidation of acetaminophen with
hydrogen peroxides in acidic medium,10 or Eu3+-tetracycline
complex binding H2O2 to form fluorescent complex in buffer
solution.11 This method has low detection limit, but it needs several
reagents, such as a fluorogenic precursor. Electrochemical
methods have been reported for the determination of hydrogen
peroxide using a platinum electrode in a supporting electrolyte12
or a copper electrode by direct and catalytic reduction.13 Although
the electrochemical method is very sensitive, it makes use of
enzymes as reagents that is unstable and expensive. Chromatographic
methods offer an alternative way of developing a sensor
for H2O2. For example, high-performance liquid chromatography
(HPLC) with fluorescence detection is used for the determination
of organic peroxides and hydrogen peroxide,14 HPLC
with electrochemical detection,15 with UV detection.16 The chromatography
can sensitively determine H2O2 in the presence of
organic peroxides; however, the equipment is also expensive and
depends on other detection. To the best of our knowledge, a H2O2
sensor based on room-temperature phosphorescence is seldom
reported.
In this study, the phosphorescence material of TiO2/SiO2
composite oxides was synthesized and its phosphorescence was
remarkably selectively quenched by H2O2 in the presence of
common ions, acids, and bases. The phosphorescence of TiO2/
SiO2 composite oxide can be recovered in hydroxylamine hydrochloride
solution and exhibit good linear response to H2O2
concentration ranging from 7.0 10-6 to 7.0 10-2 M. This
method was successfully applied to H2O2 determination in com-
* To whom correspondence should be addressed. E-mail: [email]xiaodan@scu.edu.cn[/email].
† College of Chemistry.
‡ College of Chemical Engineering.
(1) Green, W. H.; Le, K. P.; Grey, J.; Au, T. T.; Sailor, M. J. Science 1997, 276,
1826-1828.
(2) Mazzio, E. A.; Soliman, K. F. A. J. Appl. Toxicol. 2004, 24, 99-106.
(3) Komazaki, Y.; Inoue, T.; Tanaka, S. Analyst 2001, 126, 587-593.
(4) Zayats, M.; Baron, R.; Popov, I.; Willner, I. Nano Lett. 2005, 5, 21-25.
(5) Klassen, N. V.; Marchington, D.; McGovan, H. C. E. Anal. Chem. 1994,
66, 2921-2925.
(6) Zhu, M.; Huang, X.; Liu, L.; Shen, H. Talanta 1997, 44, 1407-1412.
(7) Matsubara, C.; Kudo, K.; Kawashita, T.; Takamura, K. Anal. Chem. 1985,
57, 1107-1109.
(8) Tanner, P. A.; Wong, A. Y. S. Anal. Chim. Acta 1998, 370, 279-287.
(9) Mori, I.; Takasaki, K.; Fujita, Y.; Matsuo, T. Talanta 1998, 47, 631-637.
(10) Jie, N.; Yang, J.; Huang, X.; Zhang, R.; Song, Z. Talanta 1995, 42, 1575-
1579.
(11) Wolfbeis, O. S.; Durkop, A.; Wu, M.; Lin, Z. Angew. Chem., Int. Ed. 2002,
41, 4495-4498.
(12) Harrar, J. E. Anal. Chem. 1963, 35, 893-896.
(13) Somasundrum, M.; Kirtikara. K.; Tanticharoen, M. Anal. Chim. Acta 1996,
319, 59-70.
(14) Wang, K.; Glaze, W. H. J. Chromatogr., A 1998, 822, 207-213.
(15) Osborne, P. G.; Yamamoto, K. J. Chromatogr., B 1998, 707, 3-8.
(16) Pinkernell, U.; Effkemann, S.; Karst, U. Anal. Chem. 1997, 69, 3623-3627.
Anal. Chem. 2007, 79, 3695-3702
10.1021/ac0624142 CCC: $37.00 © 2007 American Chemical Society Analytical Chemistry, Vol. 79, No. 10, May 15, 2007 3695
Published on Web 04/20/2007
mercial samples. The primary interest of this work is to develop
the TiO2/SiO2 composite oxide to the analysis of H2O2 for the
first time.
EXPERIMENTAL SECTION
Chemicals. Tetraethoxysilane, isopropyl alcohol, and hydroxylamine
hydrochloride were obtained from Chengdu Chemicals
(Sichuan, China). Tetrabutyl titanium was purchased from Shanghai
Chemicals (Shanghai, China). A 30% H2O2 aqueous solution
was obtained from Chongqing Chemicals (Chongqing, China).
All chemicals were of analytical reagent grade and were used
without further purification. A stock solution of 1 10-2MH2O2
was prepared by 30% H2O2 solution and diluted with redistilled
water. The H2O2 standard solution was standardized by KMnO4,
which was previously standardized by sodium oxalate. Redistilled
water was used throughout all experiments.
Instrumentation. Phosphorescence measurements were performed
at room temperature using a fluorescence spectrophotometer
F-4500 (Hitachi). Infrared (IR) spectra were performed
on a FI-IR670 infrared spectrophotometer (Nicolet Corp.). The
electron spin resonance (ESR) spectra were recorded on a Bruker
ER200D-SRC. Microwave frequency was 9.44 GHz. X-ray absorption
spectra (Ti K edge at 4.996 keV) were measured at the
National Synchrotron Radiation Laboratory (NSRL). Scanning
electron microscopy (SEM) image was captured by a JSM-5900LV
scanning electron microscope (JEOL). XPS analysis was performed
on a V4105 X-ray photoelectron spectroscopy instrument
(Noran).
Preparation of the TiO2/SiO2 Composite Oxide. The
nanometer particles of TiO2/SiO2 composite oxides were prepared
by the sol-gel method according to the literature.17-20 Tetrabutyltitanium
and tetraethoxysilane were selected as the source of
Ti and Si, respectively. Tetraethoxysilane was dissolved in isopropyl
alcohol, and then the solution was stirred continuously for
20 min. Tetrabutyltitanium was dripped into the solution. Distilled
water was injected drop by drop until a transparent sol formed
and gelled at room temperature. The molar ratio of Si and Ti was
1:4.6. Finally, calcinations were performed at 550 °C for 1 h, and
nanometer-sized TiO2/SiO2 particles were obtained. (Warning: The
isopropyl alcohol is flammable; keep fume hood closed and ensure
the system is away from flames and sparks. Isopropyl alcohol can
be volatilized during the calcinations of the gels. Therefore,
calcinations should be done in a well-ventilated fume hood.) The
composite oxide was then kept in the desiccators and triturated
before use.
Measurement Procedure. Phosphorescence measurements
of the sensor were carried out on a fluorescence-phosphorescence
spectrophotometer in the absence and presence a series of H2O2
solutions (7 10-7-7.0 10-2 M). The powder of TiO2/SiO2
composite oxides was pressed into disks of 12 mm in diameter
and 0.5 mm in thickness. The response of the sensors to H2O2
solutions of different concentrations was detected in a flow cell
(Supporting Information Figure S1). A 10.0-mL sample of H2O2
was manually injected into the flow cell before it was determined.
The time scan phosphorescence spectra were obtained at the
maximum excitation wavelength of 403 nm and the emission
wavelength of 535 nm. The wavelength scan phosphorescence
spectra were also excited at 403 nm, and the emissions ranged
from 450 to 650 nm. The excitation and emission bandwidth slits
were set at 10 and 20 nm, respectively.
RESULTS AND DISCUSSION
The nanometer particles of TiO2/SiO2 composite oxides were
prepared by a sol-gel method according to the literature.17-20 The
molar ratio of Si and Ti was 1:4.6. Calcinations were finally
performed at 550 °C for 1 h to obtain nanometer-sized TiO2/SiO2
particles.
The phosphorescence intensity and experimental condition can
be seen in Table S1 (Supporting Information). When the Ti/Si
molar ratio was equal to 1:4.6, the phosphorescence intensity of
TiO2/SiO2 was stronger than that of Ti:Si ) 1:1.5 and Ti:Si ) 1:7.5.
The phosphorescence intensity of TiO2/SiO2, which was calcined
at 550 °C for 1 h, is the strongest of all. If the calcination
temperature exceeded 600 °C, the TiO2/SiO2 composite oxides
have no phosphorescence.
A morphological study of the material was carried out by SEM.
Figure S2 (Supporting Information) shows the SEM image of the
material (Ti/Si molar ratio is 1:4.6) obtained at 550 °C for 1 h.
The particle diameter was from 20 to 50 nm. Fourier transform
infrared of composite oxides is shown in Figure 3. The IR band
observed at 910-960 cm-1 is widely accepted as the characteristic
vibration due to the formation of Ti-O-Si bonds.21,22 This
indicates that Ti substitutes for Si, which is assumed to form the
trap levels. This results in the broadband phosphorescence
(Scheme 1). When the gel is calcined at much higher temperature
(>600 °C), the “Ti-O” bond is very stable. It is difficult to produce
traps and cannot form the defect, so there is no phosphorescence
observed.
XPS analysis was performed on the TiO2/SiO2 composite oxide
sample. Figures 1 and 2 show XPS core level spectra for the TiO2/
SiO2 composite oxide sample before and after adding H2O2.
According to the literature,23 the binding energies of Ti 2P3/2 for
the different oxidation states of titanium are positioned on the
graph as follows: Ti0 at 454.1 eV; Ti2+ at 455.3 eV; Ti3+ at 457.2
eV; and Ti4+ at 459.2 eV. Hence, it can be inferred from Figure 1
(the top curve) that the titanium of TiO2/SiO2 composite oxide is
mostly confined to its highest oxidation state (IV). In addition,
according to the result of the IR spectra of TiO2/SiO2 composite
oxide (Supporting Information Figure S3), the majority of framework
Ti centers are tetrahedral surrounded by four -OSi linkages.
In Figures 2 and 3, the Ti (2p) spectrum is slightly shifted to the
higher binding energy (BE) after adding H2O2; however, the Si
(2p) spectrum shifts to lower BE. This shift in binding energy is
attributed to the change in the chemical environment of the TiO2/
SiO2 composite oxide. It was reported that the Ti-O-O-Si
peroxo moieties formatted in TiO2/SiO2 composite oxide after
adding H2O2.24
(17) Yu, J.; Zhao, X.; Yu, J. C.; Zhong, G.; Han, J.; Zhao, Q. J. Mater. Sci. Lett.
2001, 20, 1745-1748.
(18) Lee, J. H.; Choi, S. Y.; Kim, C. E.; Kim,G. D. J. Mater. Sci. 1997, 32, 3577-
3585.
(19) Zhai, J. W.; Zhang, L. Y.; Yao, X.; Shi, W. S. J. Mater. Sci. Lett. 1999, 18,
1107-1109.
(20) Samantaray, S. K.; Parida, K.; Kinet, R. Catal. Lett. 2003, 78, 381-387.
(21) Jung, M. J. Sol-Gel Sci. Technol. 2000, 19, 563-568.
(22) Bordiga, S.; Coluccia, S.; Lamberti, C.; Marchese, L.; Zecchina, A.;
Boscherini, F.; Buffa, F.; Genoni, F.; Leofanti, G.; Petrini, G.; Vlaic, G. J.
Phys. Chem. 1994, 98, 4125-4132.
(23) Mayer, J. T.; Diebold, U.; Madey, T. E.; Garfunkel, E. J. Electron Spectrosc.
1995, 73, 1-11.
3696 Analytical Chemistry, Vol. 79, No. 10, May 15, 2007
Electron spin resonance (ESR) spectroscopy was used to detect
and identify radicals formed after TiO2/SiO2 composite oxide
interaction with H2O2 solution. As shown in Figure 3, no ESR
signal was detected for the material. However, after reaction with
H2O2 solution, one signal appeared at gz ) 2.0200, gy ) 2.0094,
and gx ) 2.0034, which is assigned to superoxide O2
-.25 This
indicated that H2O2 was a prerequisite for the formation of this
radical addict.
X-ray absorption fine structure (XAFS) spectra were analyzed
by the Athena and Artemis program in the IFEFFIT computer
package.26 To obtain more detailed information about the Ti local
environment in the TiO2/SiO2 composite sample, an extended
X-ray absorption fine structure (EXAFS) spectrum was fitted to
(24) Munakata, H.; Ozumi, Y.; Miyamoto, A. J. Phys. Chem. B 2001, 105, 3493-
3501.
(25) Bonoldi, L.; Busetto, C.; Congiu, A.; Marra, G.; Ranghino, G.; Salvalaggio,
M.; Spano, G.; Giamello, E. Spectrochim. Acta A 2002, 58, 1143-1154.
(26) Rehr, J. J.; Mustre de Leon, J.; Zabinsky, S. I.; Albers, R. C. J. Am. Chem.
Soc. 1991, 113, 5135-5140.
Figure 1. XPS of the Ti (2p) of TiO2/SiO2 composite oxide sample (a) before and (b) after adding H2O2.
Figure 2. XPS of the Si (2p) of TiO2/SiO2 composite oxide sample (a) after and (b) before adding H2O2.
Figure 3. ESR spectra of Ti-Si material before (a) and after (b)
treatment with H2O2 solution.
Scheme 1. Proposed Phosphorescence
Excitation/Emission Mechanism of TiO2/SiO2
Composite Oxide
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