Supplementary Material
Template-free synthesis of single-/double-walled TiO2 nanovesicles:
potential photocatalysts for engineering application
Gongde Chen, He Cheng, Weixin Zhang*, Zeheng Yang, Maoqin Qiu, Xiao Zhu, and Min Chen
School of Chemistry and Chemical Engineering, Anhui Key Laboratory of Controllable Chemical
Reaction & Material Chemical Engineering, Hefei University of Technology, Hefei, Anhui 230009,
PR China
*
Correspondence concerning this article should be addressed to W. Zhang at wxzhang@hfut.edu.cn.
Experimental Section
Sample preparation
All chemicals used in this study were purchased from Sinopharm Chemical Reagent Co., Ltd,
China, and used as-received without further purification. Anatase TiO2 nanovesicles were prepared
by controllable hydrolysis Ti(SO4)2 in the presence of the H2O2 and urea. Typically, 5 mL of H2O2
(30 wt%) was mixed with 30 mL of Ti(SO4)2 aqueous solution (0.1 mol/L). Then, 3 g of urea (≥99.0
wt%) was dissolved into the solution above and the mixed solution was subsequently transferred into
a 60 mL Teflon-lined stainless steel autoclave. After being heated in an oven at 170 oC for 2 or 16 h,
the products were collected, washed with distilled water and ethanol for three times, respectively, and
dried in the oven at 60 oC overnight.
Characterization
The samples were characterized by X-ray powder diffraction (XRD) in a Rigaku D/max-γB X-ray
diffractometer with a Cu kα radiation source (λ= 0.154178 nm) operated at 40 kV and 80 mA. The
scanning rate was 4o/min, and the step width was 0.02o. The morphologies and structures of the
samples were characterized using field-emission scanning electron microscope (FESEM) (FEI
Sirion-200) and high resolution TEM (HRTEM) (JEM-2100F) at an accelerating voltage of 200 kV.
Photoluminescence (PL) spectra were recorded at room temperature on a fluorescence
spectrophotometer (Hitachi F-4500) with a Xenon lamp (150 W) as the excitation source. Both
entrance and exit slits were 5.0 nm and the scanning speed was 1200 nm/min. Diffuse reflectance
UV-visible spectra within a wavelength range of 200-800 nm were recorded on a Shimadzu 2550
UV-visible spectrometer and BaSO4 powder was used as the internal standard.
N2 adsorption-desorption isotherms were recorded on a Quantachrome NOVA 2200e surface area
and pore size analyzer at liquid nitrogen temperature. All samples were degassed at 120 oC for 4 h
prior to measurements. The specific surface area of the samples was calculated by following the
multi-point BET (Brunauer-Emmett-Teller) procedure, and the average pore diameter was determined
by the Barrett-Joyner-Halenda (BJH) method using the desorption isothermal.
Photocatalytic activity measurement
The photocatalytic activities of the samples with regard to RhB in aqueous solution were evaluated
under a UV light irradiation at a distance of 10 cm. A high-pressure Hg lamp (predominant
wavelength λ=365 nm, 300 W) was used as the light source. Typically, 0.05 g of samples were
dispersed in 100 mL of RhB aqueous solution with an initial concentration of 1×10-5 or 2×10-5 mol/L,
and then magnetically stirred in the dark for 4 h to reach adsorption equilibrium. The suspension was
then exposed to a 300 W of high-pressure Hg lamp. A 2 mL of solution was drawn from the system at
a certain time interval. After removal of the catalyst by centrifugation, residual RhB concentration
was determined through detecting its characteristic emission peak intensity at 586 nm on a Hitachi
F-4500 fluorescence spectrophotometer or characteristic adsorption peak intensity at 553 nm on a
Shimadzu 2550 UV-visible spectrometer.
Characterization of Hydroxyl Radicals
Hydroxyl radicals (·OH) produced on the surface of TiO2 photocatalysts were detected by a
photoluminescence (PL) technique. Terephthalic acid was used as the probe molecule due to its easy
reaction with ·OH to produce 2-hydroxyl-terephthalic acid, which has a high fluorescent signal at
around 425 nm when excited by 315 nm light23-25. The PL intensity of 2-hydroxyl-terephthalic acid
was proportional to the amount of ·OH produced on the surface of TiO2 photocatalysts. The
experimental procedure was similar to the photocatalytic experiment except that RhB solution was
replaced by the basic terephthalic acid solution (5×10-4 mol/L) with NaOH (2×10-3 mol/L). The
withdrawn solution after centrifugation was measured on a Hitachi F-4500 fluorescence
116
213
204
105
211
s2
200
a
103
112 004
Intensity (a.u.)
101
spectrophotometer with the excitation wavelength of 315 nm.
s1
20
30
70
-1
)
-1
0.04
0.03
b
3
dV/dD (cm g nm
180
3
Volume absorbed (cm g
-1
)
210
40
50
60
2Theta (degrees)
150
120
0.02
0.01
0.00
0
20 40 60 80 100
Pore diameter (nm)
90
60
s1
s2
30
0
0.0
0.2
0.4
0.6
0.8
Relative pressure (P/P0)
1.0
Figure S1. (a) XRD patterns and (b) N2 absorption-desorption isothermal curves of the samples
prepared by a hydrothermal treatment of Ti(SO4)2 with the assistance of H2O2 and urea for (s1) 2 h
and (s2) 16 h. The insets show the corresponding pore size distribution calculated by the BJH
method.
a
b
2 μm
c
200 nm
d
2 μm
200 nm
Figure S2. FESEM images of anatase TiO2 samples prepared by a hydrothermal treatment of
Ti(SO4)2 with the assistance of H2O2 and urea for (a, b) 2 h and (c, d) 16 h.
H 2 Ti 5 O 11 ·3H 2 O
Nanosheet Assembly
Nanoparticles
Ti(SO4)2
Nucleation
Growth
H2O2
15 min
Urea
30 min
Ripening
Hydrothermal Reaction 170 °C
Ripening
16 h
Double-walled
Anatase TiO 2
Nanovesicle
Ripening
2h
Single-walled
Anatase TiO 2
Nanovesicle
1h
Anatase
TiO 2 / H 2 Ti 5 O 11 ·3H 2 O
Core-shell Structure
Figure S3. Schematic illustration of the formation process for single- and double-walled anatase TiO2
nanovesicles.
Intensity (a.u.)


b

10
20
30
40
50
2Theta (degrees)
a
60
70
a
b
100 nm
Figure S4. XRD patterns and TEM images of the samples prepared by a hydrothermal treatment of
Ti(SO4)2 with the assistance of H2O2 and urea for (a) 0.5 h and (b) 1 h.
1.0
C/C0
0.8
0.6
0.4
0.2
a
b
0.0
0
30
60
90 120 150 180 210 240
Time (min)
Figure S5. The adsorption curves of RhB solution (initial concentration: 1×10-5 mol/L) over (a)
single- and (b) double-walled anatase TiO2 nanovesicles.
Detection of hydroxyl radicals
Active species ·OH radicals generated on the surface of single- and double-walled anatase TiO2
nanovesicles and commercial anatase TiO2 nanoparticles were probed by terephthalic acid solution.
As shown in Fig. S6, the PL intensity at around 425 nm increases with the irradiation time, indicating
that the amount of ·OH radicals generated on the surface of photocatalysts increases with the time.
The sequence of the samples based on the PL intensity detected from high to low is double-walled
anatase TiO2 nanovesciles, single-walled anatase TiO2 nanovesciles, and commercial anatase TiO2
nanoparticles in turn. The result indicates that double-walled anatase TiO2 nanovesciles are able to
produce more ·OH radicals than single-walled ones possibly because the former possess higher
crystallinity than the latter, which leads to lower recombination rate for electron-hole pairs on the
former than the latter. They both generate more ·OH radicals than commercial anatase TiO2
nanoparticles, which may result from their enhanced light absorption capacity.
8000
PL intensity (a.u.)
7000
a
6000
5000
3000
60 min
40 min
20 min
2000
10 min
4000
0 min
1000
0
350
400
450
500
550
Wavelength (nm)
600
8000
PL intensity (a.u.)
7000
6000
b
60 min
40 min
20 min
5000
4000
10 min
3000
0 min
2000
1000
0
350
400
8000
PL intensity (a.u.)
7000
450
500
550
Wavelength (nm)
600
c
6000
5000
4000
60 min
40 min
20 min
3000
2000
10 min
1000
0
350
0 min
400
450
500
550
Wavelength (nm)
600
Figure S6. Fluorescence spectral changes of terephthalic acid solution under UV light irradiation in
the presence of (a) single-walled anatase TiO2 nanovesicles, (b) double-walled anatase TiO2
nanovesicles, and (c) commercial anatase TiO2 nanoparticles.
Light absorption properties
1.4
a
b
c
Absorbance (a.u.)
1.2
1.0
0.8
0.6
0.4
0.2
0.0
200
300
400 500 600
Wavelength (nm)
700
800
Figure S7. Diffuse reflectance UV-vis absorption spectra of the samples: (a) single-walled anatase
TiO2 nanovesicles, (b) double-walled anatase TiO2 nanovesicles, and (c) commercial anatase TiO2
nanoparticles.
Fig. S7 shows the diffusion reflectance UV-vis absorption spectra of anatase TiO2 nanovesicles
and commercial anatase TiO2 nanoparticles. As presented, the absorption edges of the three samples
are almost the same because they have the same intrinsic energy band gap. Furthermore,
single-walled anatase TiO2 nanovesicles exhibit very similar absorption spectrum to double-walled
anatase TiO2 nanovesicles. They both exhibit superior light absorption capacity to commercial
anatase TiO2 nanoparticles within the wavelength range from 200 to 335 nm.




  


20
30
40
50
2Theta (degree)




60


70
200 nm
-1
3
180
-1
210
)
240
dV/dD (cm g nm
3
Volume absorbed (cm g
-1
)
10
b
anatase 
rutile #
Intensity (a.u.)
a
150
120
90
c
0.0050
0.0045
0.0040
0.0035
0.0030
0.0025
0.0020
0.0015
0
60
20
40
60
80
Pore diameter (nm)
100
30
0
0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (P/P0)
Figure S8. (a) XRD pattern and (b) TEM image and (c) N2 absorption-desorption isothermal curves
of P25. The inset shows the corresponding pore size distribution calculated by the BJH method.
Life cycle assessment
Life cycle experiments were conducted to assess the durability of single- and double-walled
anatase TiO2 nanovesicles, and the corresponding results are presented in Fig. S9. The spent
photocatalysts were collected, cleaned by deionized water, and dried for use after each run. The
photocatalysts repeated to degrade RhB solution (1×10-5 mol/L, 100 mL) under UV light irradiation
for 5 times. As observed, RhB degradation ratio decreases gradually with the increase of run cycles.
After five cycles, RhB degradation ratio can still reach 81.0 and 82.8% over single- and
double-walled anatase TiO2 nanovesicles, respectively. The results indicate that they possess good
stability as photocatalysts.
1.0
a
C/C0
0.8
0.6
0.4
0.2
0.0
2nd run 3rd run
1st run
0
1.0
3
4th run
6
9
Time (h)
5th run
12
15
b
C/C0
0.8
0.6
0.4
0.2
0.0
2nd run 3rd run
1st run
0
3
4th run
6
9
Time (h)
5th run
12
15
Figure S9. Life cycle performances of (a) single- and (b) double-walled anatase TiO2 nanovesicles in
the photocatalytic degradation of RhB solution (1×10-5 mol/L) under UV light irradiation.
Table 1
Crystallite
Sample
single-walled anatase
TiO2 nanovesicles
double-walled anatase
TiO2 nanovesicles
commercial anatase
TiO2 nanoparticles15
Degussa P25-TiO2 c
size (nm)a
Particle
size (nm)
Wall Thickness
(nm)
Specific
surface
area (m2/g)
Average
pore
size (nm)
Pore
volume
(cm3/g)
10.4
400-500b
ca. 100
170.1
3.76
0.215
39.9
400-500b
ca. 30 (inner)
ca. 50 (outer)
106.2
7.59
0.290
49.8
ca. 100
N/A
8.9
4.80
0.050
22.6
ca. 30
N/A
36.4
3.19
0.341
a
: Crystallite size was calculated by Scherrer formula based on the peak width at half height of the diffraction peak
assigned to (101) plane of anatase TiO2.
b
c
: The average size of single nanovesicle unit obtained from Fig. 1 and Fig. S2.
: The textural properties of P25 was obtained from Fig. S8.