Supplementary Information (SI)
Solvothermal Synthesis of Designed Non-stoichiometric Strontium Titanate for Efficient
Visible-Light Photocatalysis
Uyi Sulaeman, Shu Yin and Tsugio Sato
IMRAM Tohoku University, Sendai, 980-8577, Japan
Experimental
SrTiO3 powders were synthesized by microwave-assisted solvothermal reactions using
Ti(OC3H7)4 and SrCl2.6H2O as starting materials with various molar ratios. The Sr/Ti atomic ratio
was adjusted to 0.8, 0.9, 1.0, 1.1, 1.25, 1.67 and 2.0. After dissolving 1.42 g of Ti(OC3H7)4 in 5 mL
of 2-prophanol, a desired amount of SrCl2.6H2O aqueous solution and 10 mL of 2 M KOH aqueous
solution were slowly added under stirring, respectively. After that the solution was introduced into a
Teflon vessel, and then the microwave-assisted solvothermal reaction was carried out at 200oC for 3h.
After cooling, the powder products were separated by centrifugation, washed with distilled water and
acetone three times, respectively, and dried in vacuum at 60oC overnight
1
The powder product was characterized by X-ray diffraction analysis (XRD, Shimadzu XD-D1)
using graphite-monochromized CuKα radiation. Lattice constant was determined using Si as an
internal standard. Microstructures were observed by transmission electron microscopy (TEM, JEOL
JEM-2010). The chemical compositions were analyzed by energy dispersive X-ray spectrometry
(EDX, EDX-800HS) using high precision standard curve method. The binding energies of Sr, Ti and
O were measured at room temperature using an electron spectrometer (Perkin Elmer PHI 5600). The
peak position of each element was corrected by using that of C1s (284.6 eV).
Photocatalytic activity was determined by measuring the concentration of NO gas at the outlet
of the reactor (373 cm3) during photoirradiation by a constant flow of 1 ppm NO-50 vol.% air
(balanced N2) mixed gas (200 cm3 min-1) [S.Yin, B. Liu, P. Zhang,T. Morikawa, K. Yamanaka, and T.
Sato, J. Phys. Chem. C, 112 (2008)12425]. The photocatalyst sample was placed in a hollow 20 mm
in length, 16 mm in width, and 0.5 mm in depth on a glass holder plate and set in the bottom center
of the reactor. Light wavelength was controlled by selecting various types of light emitting diode
(LED) lamps (OptiLED, SP-E27, 2.5 W) with different light wavelength distributions. Photocatalytic
characterizations were carried out using different LED lamps at the same light irradiation intensity of
2 mW/cm2 on the sample surfaces by controlling the distance between the lamps and surfaces under
continuous irradiation by monochromatic lights of 390 nm (UV LED), 445 nm (blue LED), 530 nm
(green LED), and 627 nm (red LED) in wavelength. The concentration of NOx was determined using
a NOx analyzer (Yanaco, ECL-88A).
2
Diffuse reflectance spectra, compositions and band gaps of the samples
Figure SI-1 show the diffuse reflectance spectra of the samples with various Sr/Ti atomic
ratios. It can be seen that the samples of the Sr/Ti atomic ratio of 0.9 and 1.0 showed only one
absorption edge around 400 nm corresponding to the band gap energy of SrTiO3, however, the
samples with the Sr/Ti atomic ratio of 0.8, 1.1, 1.25, 1.67 and 2 showed the visible light absorption
(400-600 nm) as well as UV light absorption (< 400 nm). The order of absorption in the visible light
region (400-600 nm) was 2.0>1.67>1.1>1.25>>0.8>1.0= 0.9, indicating that the visible light
absorption tends to increase with an increase in the amounts of both Sr and Ti deficient in the sample.
This might be due to the formation of oxygen vacancy.
The values of the band gap energies of the samples calculated from the absorption edges of the
spectra are also listed in Table SI-1.
1.2
1
Sr/Ti=0.8
Sr/Ti=0.9
Sr/Ti=1
Sr/Ti=1.1
Sr/Ti=1.25
Sr/Ti=1.67
Sr/Ti=2
Absorption
0.8
0.6
0.4
0.2
0
200
300
400
500
600
700
800
Wavelength/nm
Figure SI-1. Diffuse reflectance spectra of the samples with various Sr/Ti atomic ratios
3
Table SI-1. Compositions and band gaps of the samples
Sr/Ti
Composition of the product determined
Composition in the initial solution
Band Gap
atomic
by EDX Analysis
ratio
Sr/Ti
Ti(IV)
Sr(II)
described
Ti(IV)
(mmol)
(mass %)
1st band
2nd
atomic
gap
Band Gap
ratio
(eV)
(eV)
Sr(II)
atomic
(mmol)
Sr/Ti
Mass %)
ratio
0.80
5.01
3.999
0.798
28.19
35.23
0.807
3.23
-
0.90
4.98
4.499
0.904
26.95
36.89
0.884
3.23
-
1.00
5.01
4.996
0.997
22.42
36.54
1.053
3.20
-
1.10
4.47
4.995
1.118
22.76
40.82
1.159
3.15
2.17
1.25
3.98
4.997
1.256
22.11
41.31
1.207
3.23
2.04
4