Advances in Nanoparticles, 2013, 2, 6-10 Published Online February 2013 (
Synthesis of La/N Co-Doped SrTiO3 Using Polymerized
Complex Method for Visible Light Photocatalysis
Uyi Sulaeman1, Shu Yin2, Tsugio Sato2
1Department of Chemistry, Jenderal Soedirman University, Purwokerto, Indonesia
2Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan
Received December 16, 2012; revised January 15, 2013; accepted January 25, 2013
Lanthanum and nitrogen co-doped SrTiO3 was synthesized using polymerized complex method with Ti(OC3H7)4,
SrCl2·6H2O and La(NO3)3·6H2O as starting materials followed by calcinations in NH3. Ethylene glycol and anhydrous
citric acid were used as the precursors of synthesis. The samples were characterized using XRD, TEM, DRS, BET,
EDX and XPS. The cubic-perovskite type of La/N co-doped SrTiO3 nanoparticle could be successfully synthesized. The
photocatalytic activity of SrTiO3 for DeNOx ability in visible light region (λ > 510 nm) could be improved by co-doping
of La3+ and N3. The high visible light photocatalytic activity of this substance was caused by a narrow band gap energy
that enables to absorb visible light.
Keywords: Photocatalysis; Visible Light; SrTiO3; Polymerized Complex; La-Doping; N-Doping
1. Introduction
Recently, synthesis of strontium titanate based photo-
catalyst for converting visible light energy to photoreac-
tion has been a great attention [1-6]. Among the modify-
ing of SrTiO3, doping with nitrogen is the most effective
to enhance photoreaction in visible light. The mixing of
N 2p with O 2p states narrows the band gap energy and
enhances the photocatalytic ability in visible light. How-
ever, substituting O2 by N3 will generate residual ani-
onic vacancies which suppress the photocatalytic activity
of SrTiO3. To solve this problem, co-doping of lantha-
num and nitrogen into SrTiO3, can decrease the band gap
energy without forming lattice defect and lattice strain,
and consequently lead to generate high visible light
photocatalytic activity. The La3+ can substitute Sr2+
without large lattice strain because of the similar ionic
Many researchers had developed the synthesis of La/N
co-doped SrTiO3 catalysts. Miyauchi et al. [7] reported
that the synthesis of La/N co-doped SrTiO3 catalysts us-
ing sol-gel method decreased the ionic vacancy and then
increased the photocatalytic activity in a visible light.
Wang et al. [8] found that the synthesis of La/N co-
doped SrTiO3 catalysts using mechanochemical reaction
enhanced the photocatalytic activity in a visible light.
However, they had a large particle and low specific sur-
face area which limited the catalytic ability. To improve
the potocatalytic ability, synthesis of fine particle which
has a large specific surface area should be realized.
Polymerized complex method using citric acid and
ethylene glycol as polymeric precursors has been widely
used for metal oxide synthesis [9,10]. The polymerized
complex process has great advantages over other synthe-
sis techniques due to mixing of several components in
atomic scale, good stoichiometry control, high purity,
low cost and relatively low processing temperature [11].
The metallic ions are dispersed in the polymeric network
at the atomic scale without precipitation and phase seg-
regation [12]. Based on this consideration, the fine parti-
cles of La-doped SrTiO3 could be synthesized by the
polymerized complex process and then followed by cal-
cinations in ammonia to obtain the La/N co-doped SrTiO3
In the present paper, we report the synthesis of La/N
co-doped SrTiO3 using polymerized complex method.
The lanthanum and nitrogen co-doping effectively nar-
rowed the band-gap energy of SrTiO3. The photocatalytic
activity of SrTiO3 for NO decomposition in visible light
region (λ > 510 nm) could be enhanced. The high visible
light photocatalytic activity of this substance might be
caused by the low band gap energy and high specific
surface area.
2. Experiment
2.1. Preparation of Catalyst
The La/N co-doped SrTiO3 with variation of lanthanum
doping was prepared by the polymerized complex method
opyright © 2013 SciRes. ANP
[9]. The Ti(OC3H7)4 and SrCl2·6H2O and La(NO3)3·6H2O
were dissolved in ethylene glycol. As amount of 38.2
gram of anhydrous citric acid and 100 mL of methanol
were added to the solution and the mixture was stirred at
130˚C until a transparent gel was formed. The polymer
was carbonized at 350˚C and calcined in air at 620˚C for
2 h to remove carbon, and the product (Sr1xLaxTiO3)
was grinded. The products of Sr1xLaxTiO3 were then
nitrogenized by heating at 700˚C for 5 h under NH3 (flow
rate 400 ml/L). The as-prepared sample of Sr1-xLax-
TiO3-yNy with x = 0, 0.25, 0.5, 0.7 and 1 are named as
STN, STN-0.25, STN-0.5, STN-0.7 and LTN, respec-
2.2. Characterization
The powder product was characterized by XRD (Shima-
dzu XD-D1) using graphite-monochromized CuKα ra-
diation. The mean crystallite size of the powders was
determined by the XRD-Scherrer equation [13]. Micro-
structure examinations were obtained by transmission
electron microscopy (TEM, JEOL JEM-2010). The band
gap energies of the products were determined using DRS
(Shimadzu UV-2000). The chemical compositions were
analyzed by EDX (Shimadzu, EDX-800HS). The spe-
cific surface area was determined by the nitrogen adsorp-
tion at 77 K (BET, Quantachrome NOVA 4200e). Bind-
ing energies of element were analyzed at room tempera-
ture by XPS (Perkin-Elmer PHI5600).
2.3. Photocatalytic Activity
The photocatalytic activities were evaluated using NOx
analyzer (Yanaco, ECL-88) [5]. A 450 W high-pressure
mercury arc was used as the light source. The wave-
length of the irradiation light was controlled by selecting
filters, i.e., Pyrex glass for λ > 290 nm, Kenko L41 Super
Pro (W) filter λ > 400 nm and Fuji, tri-acetyl cellulose
filter λ > 510 nm. The photocalyst sample was placed in
a hollow of 20 mm length × 15 mm width × 0.5 mm
depth on a glass holder plate and set in the bottom center
of the reactor. The concentration of NO gas at the outlet
of the reactor during the photoirradiation was monitored
for 10 minutes for every filter.
3. Result and Discussion
3.1. XRD Analysis
The XRD profiles of La/N co-doped SrTiO3 are shown in
Figure 1. The single phase of cubic-perovskite could be
observed at samples of STN, STN-0.25 and STN-0.5,
while the sample of LTN contains an impurity. The in-
tensity of diffraction decreased with increasing La dop-
ing, indicating that the crystalline properties was strongly
affected by La doping. The particle sizes of La/N co-
doped SrTiO3 calculated by Scherrer equation are listed
in Table 1. The particle of 52 nm could be obtained in
the sample of STN, and decreased with increasing La
doping to 39 nm, 17 nm, 23 nm and 18 nm for STN-0.25,
STN-0.5, STN-0.7 and LTN, respectively. The smallest
of particle size could be found on the sample of STN-0.5.
3.2. Morphology
Figure 2 shows the morphology of STN and STN-0.5.
The particle size of 40 - 60 nm in diameter could be ob-
served in STN and 15 - 20 nm in STN-0.5. The particle
size observed by TEM agreed with that measured by
Scherrer equation (see Table 1). The particle size of
STN-0.5 is smaller than that of STN, indicating that the
La doping affected the process of crystallization.
3.3. Uv-Vis Diffusion Reflectance Spectroscopy
Figure 3 shows the absorbance spectra of La/N co-doped
SrTiO3. The absorption edge shifted to higher of wave-
length, indicating the narrow band gap was generated by
La/N co-doping. The band-gap energies of La/N co-doped
10 20 3040 5060 70 80
Figure 1. XRD patterns of La/N co-doped SrTiO3 samples
synthesized by the polyme rized co mple x me thod.
Table 1. The crystallite sizes, specific surface areas, Sr/Ti
and La/Ti atomic ratios from EDX of La/N co-doped
SrTiO3 synthesized by the polymer i zed complex me thod.
Sample Crystallite
Size (nm)
Specific Surface
Area (m2/g)
Ratio Sr/Ti
Ratio La/Ti
STN 52 17.30 1.076 -
STN-0.2539 25.75 0.757 0.218
STN-0.517 65.43 0.467 0.443
STN-0.723 30.36 0.280 0.653
LTN 18 58.25 - -
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Figure 2. TEM images of STN (a) and STN-0.5 (b) synthe-
sized by polymeri zed comple x method.
200 300 400 500600 700 800
Figure 3. DRS of La/N co-doped SrTiO3 synthesized using
polymer complex method.
SrTiO3 were calculated according to the equation of Eg =
1240/λ [14]. The results were 2.95, 1.87, 2.13, 2.16 and
2.08 eV for STN, STN-0.25, STN-0.5, STN-0.7 and LTN,
respectively. The variations of color could be observed in
the samples, they are grey, blue, greenish-yellow and
yellow, for STN, STN-0.25, STN-0.5, STN-0.7, respec-
tively. The highest band gap energy of 2.95 eV could be
observed for STN, indicating that the doping of nitrogen
without lanthanum did not effectively narrow the band
gap energy.
The broad absorption above 500 nm could be found in
the spectra of STN and STN-0.25. The sample of STN-
0.25 showed high broad absorption which was assigned
to the oxygen vacancy states. They were located between
0.75 and 1.18 eV below the minimum level of the con-
duction band [15]. The similar results were also found in
the samples prepared with different methods [7]. The
strontium titanate with oxygen vacancies can absorb a
broad range of visible light above 500 nm. The lower
broad absorption above 500 nm could be found in the
sample of STN-0.5, STN-0.7 and LTN, indicating that
the samples have lower oxygen vacancy.
3.4. XPS Analys is
Figure 4 shows XPS profiles of the STN-0.5 after sput-
tering at 3 kV for 3 minutes. The peak N1s could be ob-
served at 396.0 eV shown in Figure 4(a), indicating the
formation of nitrogen doped SrTiO3 [7]. This result
proves that nitrogen was incorporated in the lattice. The
lanthanum ion could be identified at 833.7 eV and 850.5
eV (Figure 4(b)), which correspond to La 3d5/2 and La
3d3/2, respectively [16]. The spectrum for titanium ex-
hibits two different signals corresponding to the Ti 2p3/2
and 2p1/2 with binding energies of 457.5 and 463.2 eV,
respectively. The peak position of Ti 2p3/2 agreed with
that of the Ti4+ [17-19]. The peak of O1s was observed at
529.1 eV which is the characteristic of metal oxides [20].
3.5. Photocatalytic Activity
Figure 5 shows the photocatalytic activity of La/N
co-doped SrTiO3 for the NO elimination under visible
light irradiation (λ > 510 nm, λ > 400 nm), and UV light
irradiation (λ > 290 nm). It took about 10 min to reach
the steady state after light irradiation. There is no sig-
nificant activity in visible light (λ > 510) for STN, pre-
sumably due to higher band gap energy of 2.95 eV. The
sample of STN-0.25 exhibits low photocatalytic activity
both in visible light and UV light. It showed the highest
broad absorption above 500 nm which is assigned to the
oxygen vacancy states. The existences of oxygen va-
cancy increase recombination of hole-electron pairs and
then decrease the photocatalytic ability [7]. The sample
of STN-0.5 showed the highest activity under the visible
light irradiation (λ > 510 nm), i.e. , 28.8% NO could be
destructed. Moreover, the photocatalytic ability of STN-
0.5 was also higher than TiO2 (P-25) in the ultraviolet
light, i.e., 42.3% of NO could be destructed. The excel-
lent photocatalytic was attributed to both narrow band
gap energy and high specific surface area (see Table 1).
The photocatalytic activity decreased with increasing
lanthanum doping (STN-0.7 and LTN). It may be attrib-
uted to low crystallinity of the sample.
4. Conclusion
Cubic perovskite of La/N co-doped SrTiO3 nanoparticles,
Sr1xLaxTiO3yNy (x = 0, 0.25, 0.5, 0.7 and 1), could be
Copyright © 2013 SciRes. ANP
Copyright © 2013 SciRes. ANP
(a) (b)
(c) (d)
Figure 4. XPS profiles of La/N co-doped SrTiO3 (STN-0.5) synthesized using the polymerized complex method.
0510 15 20 2530
Time / min.
NO Concentration / ppm
λ>510nm λ>400n λ>290nm
Figure 5. The photocatalytic NO destruction activities of
La/N co-doped SrTiO3.
synthesized by the polymer complex (PC) method using
Ti(OC3H7)4, SrCl2·6H2O, and La(NO3)2·6H2O as starting
materials followed by calcinations in ammonia. Ethylene
glycol and anhydrous citric acid could be used as the
precursors of synthesis. The catalytic degradation of NO
over La/N co-doped SrTiO3 is significantly improved in
the presence of visible-light irradiation. The sample with
x = 0.5 is the highest photocatalytic activity for NO deg-
radation under visible light irradiation (λ > 510 nm).
5. Acknowledgements
This research was partly supported by the Management
Expenses Grants for National Universities Corporations
from the Ministry of Education, Culture, Sports, Science
for Technology of Japan (MEXT).
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