fabrication and photoactivity of hollow tio2 microspheres by chemically induced self-transformation
DESCRIPTION
Jiaguo Yu, Professor of Materials Physics and Chemistry at Wuhan University of Technology (China)TRANSCRIPT
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Fabrication and Photoactivity of Hollow TiO2 Microspheres by Chemically Induced Self-tra
nsformation
Jiaguo Yu
State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology,
Luoshi Road 122#, Wuhan 430070, P.R. China. E-mail address: [email protected].
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SCI Papers on photocatalysis published in recent 10 years
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Photocatalysis of TiO2 hollow microspheres
• due to its widely potential application in water and air purification and solar energy conversion.
• Among various oxide semiconductor photocatalysts, titania has proven to be the most suitable for widespread environmental applications.
• Fabrication of TiO2 hollow microspheres has attracted a great deal of attention because of their low density, high surface area, good surface permeability, larger light-harvesting efficiencies. higher energy conversion efficiency and photocatalytic activity.
• Here, I will report fabrication and photocatalytic activity of TiO2 hollow spheres by a chemically induced self-transformation method, a environmentally friendly method.
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Preparation of TiO2 hollow microspheres • chemically induced self-transformation method
• Crystalline mesoporous TiO2 hollow microspheres are fabricated by hydrothermal treatment of acidic Ti(SO4)2 aqueous solution in the presence of NH4F at 200oC for 9 h. The molar ratio of fluoride to titanium (R) varied from 0, 0.4, 1 to 2.
• The photocatalytic activity of the samples was evaluated by measuring the photocatalytic decomposition of acetone in air under UV irradiation.
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Ti(SO4)2
+NH4F
Step 1 Step 2 Step 3 Step 4
Step 1: explosive multiplication of large numbers of metastable TiO2 nanoclusters;
Step 2: thermodynamically spontaneous organization of TiO2 nanoclusters into amorphous spherical aggregates.
Step 3: heterogeneous nucleation of a crystalline thin shell around the amorphous spherical aggregates.
Step 4: preferential dissolution of the amorphous particle interior and the continuous deposition of a porous crystalline external shell, producing intact hollow microspheres without modification in the bulk morphology.
Scheme 1 Illustration of formation mechanism of hollow TiO2 microspheres based on fluoride-induced self-transforma
tion strategy
J. Yu, et al. Adv Funct Mater, 2006, 16, 2035
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Fig. 1. TEM (a, b, c, f) and SEM (d, e) images of TiO2 samples prepared with varying R at 200oC for 9 h: (a) 0; (b) 0.4; (c, d, e) 1; (f) 2.
J. Yu, et al. J Catal, 2007, 249, 59
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Fig. 2. EDX spectrum of anatase TiO2 hollow microspheres obtained with R = 1 at 200oC for 9 h.
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R = 0 R = 0.4
R = 1 R = 2
AmorphousPrecursor
A
C
A primary nanocrystal B secondary aggregate C triple aggregate
B
R = 0 R = 0.4
R = 1 R = 2
AmorphousPrecursor
A
C
A primary nanocrystal B secondary aggregate C triple aggregate
B
Scheme 2. Illustration for the fluoride-mediated formation of hierarchical porous TiO2 hollow microspheres and their morphology variations at varying R
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0.0 0.2 0.4 0.6 0.8 1.00
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80
120
160
200
Ads
orbe
d vo
lum
e (c
m3 /g
)
Relative pressure (P/P0)
R = 0 R = 0.4 R = 1 R = 2
1 10 1000.00
0.03
0.06
0.09
Por
e vo
lum
e (c
m3 /g
)
Pore diameter (nm)
R = 0 R = 0.4 R = 1 R = 2
Fig. 3. Nitrogen adsorption-desorption isotherms and corresponding pore size distribution of TiO2 samples prepared with varying R at 200oC for 9 h.
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Fig. 4. TEM images of TiO2 samples prepared with R = 1 at 200oC for different hydrothermal time: (a) 30 min; (b) 9 h; (c) 36 h. Inset in (a) shows the corresponding XRD pattern.
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5 min10 20 30 40 50 60 70
(A)
R = 2
R = 1
R = 0.4
R = 0
Rel
ativ
e In
tens
ity (
a.u.
)
2 Theta (degree) 0 1 25
10
15
0.08
0.16
0.2425
50
75
100
PV
(cm
3 /g)
AP
S(n
m)
R
SB
ET
(m2 /g
)
(B)
Fig. 5. (A): XRD patterns and (B): BET surface area (SBET), pore volume (PV) and average pore size (APS) of TiO2 samples with varying R at 200oC for 9 h.
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30 min
0
3
6
9
P25
R = 2R = 1R = 0.4R = 0
Rat
e co
nsta
nt (
10-3, m
in-1)
Fig. 6. The apparent rate constant of TiO2 samples prepared at 200oC for 9 h with varying R, and their comparision with that of P25.
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Conclusions
Hollow anatase-phase TiO2 microspheres with bimodel mesoporous shells can be easily fabricated on a large scale.
fluoride induces the hollowing process of TiO2 microspheres, and the rate of such a process can be readily tuned by changing R, a higher R results in a greater hollowing rate.
chemically induced self-transformation is a environmentally friendly method, can be used to produce highly active photocatalytic materials.
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the added fluoride promotes the crystallization and crystallite growth of anatase-phase TiO2 primary nanocrystals, and thus the BET surface areas decrease with increasing R. The as-prepared hollow TiO2 microspheres generally exhibit bimodal mesopore size distribution, finer intra-aggregated pores and greater inter-aggregated pores, with their maximum pore diameters in the range of 3-10 and 30-50 nm, respectively.
The positive effect of fluoride on enhancing the crystallization and increasing the pore volume at appropriate R is suggested to be the main contribution of fluoride to the improvement of photocatalytic activity of hollow TiO2 microspheres.
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Fabrication of CaCO3 Hollow Microspheres by Chemically Induced Self-Transformation
Low-magnification SEM
High-magnification SEM
J. Yu, et al. Adv Funct Mater, 2006, 16, 2035
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Fabrication of CaCO3 Hollow Microspheres by Chemically Induced Self-Transformation
TEM images
J. Yu, et al. Adv Funct Mater, 2006, 16, 2035
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Formation Mechanism of CaCO3 Hollow Microspheres
30 min 2 h 24 h
J. Yu, et al. Adv Funct Mater, 2006, 16, 2035
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Spontaneous Formation of a Tungsten Trioxide Sphere-in-Shell Superstructure by Chemically Induced Self-Transformation
J. Yu, et al. Small, 2008, 4, 87
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Formation Mechanism of a Tungsten Trioxide Sphere-in-Shell Superstructure
SrWO4WO3·nH2O
WO3·nH2O
WO3·1/3H2O
J. Yu, et al. Small, 2008, 4, 87
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Fabrication of SnO2 Hollow Structures by Chemically Induced Self-Transformation
J. Yu, et al. Adv Funct Mater, 2006, 16, 2035
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A One-Pot Approach to Hierarchically Nanoporous Titania HollowMicrospheres with High Photocatalytic Activity
J. Yu, et al. Cryst. Growth Des, 2008, 8, 930
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Formation Mechanism of Hierarchically Nanoporous Titania Hollow Microspheres
J. Yu, et al. Cryst. Growth Des, 2008, 8, 930
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Nitrogen adsorption–desorption isotherm (inset) and corresponding pore-size distribution of TiO2 hollow spheres
J. Yu, et al. Cryst. Growth Des, 2008, 8, 930
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Hydrothermal Synthesis and Photocatalytic Activity of Zinc Oxide Hollow Spheres
J. Yu, et al. Environ Sci Tech, 2008, 42, 4902
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Acknowledgment
• This work was supported by NSFC (50625208, 20773097 and 20877061) and 973 program (No. 2007CB613302).
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1 Secondary pollution and separation of nanoparticles.2 Stability of nanocatalysts in air, solution and solid.3 Thermodynamically driven self-aggregation and self-tra
nsformation of nanoparticles.4 Preparation of nanostructured hollow microspheres.5 Application of nanostructured hollow microspheres in w
ater and air purification.6 Nano-pollution and its influence on health.
Important open Questions
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Thank you
for
your attention!