Fabrication and Photoactivity of Hollow TiO2 Microspheres by Chemically Induced Self-transformation

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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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Publication Years

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97 98 99 00 01 02 03 04 05 06 07

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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

40

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


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Fabrication of CaCO3 Hollow Microspheres by Chemically Induced Self-Transformation

TEM images


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Formation Mechanism of CaCO3 Hollow Microspheres

30 min 2 h 24 h


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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


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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


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Nitrogen adsorption–desorption isotherm (inset) and corresponding pore-size distribution of TiO2 hollow spheres


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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!

Fabrication and Photoactivity of Hollow TiO2 Microspheres by Chemically Induced Self-transformation

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