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Photocatalytic activity of SBA-15 silica-supported titania photocat

alysts

王聖璋 Sheng-Chang Wang

南台科技大學Southern Taiwan University

Institute of Nanotechnology, & Department of Mechanical Engineering, Southern Taiwan University, Tainan 710, Taiwan

洪玲雅 Ling-Ya Hung 、黃肇瑞 Jow-Lay Huang

國立成功大學材料科學與工程學研究所2007/11/17

海峽兩岸工程材料研討會 新竹 - 台灣

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南台科大 Southern Taiwan UniversityLocation

Main Gate

Campus

Solar-cell car

Nanotechnology center

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Photo catalysis ehTiO h

2

*.. adsads OHOHh

*22 OOe

TiO2 :•Solar energy conversion•Catalyst•Environmental pollution remediation

Band gap of semiconductors

4

TiO2 Nanoparticle

Broader energy band gap Recombination of electron and hole was decreased. Higher adsorption surface area

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Disadvantages and strategies Problems:

• Ultrafine powders will agglomerate into larger particles • adverse effect on catalyst performance

• Separation and recovery of TiO2 powders from wastewater are difficult

• limited light transmission due to scattering

• susceptibility to sintering Strategies

• Supported TiO2 composites • High active surface area

• UV-Visible transparent, no absorption.

• Stable in chemical and thermal atmospheres

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Photocatalyst supporter activated carbon clays alumina

Zeolite, pore size < 1.5 nm Mesoporous SiO2

• MCM-41, CTABr, < 10 nm

• SBA-15, PEO20-PPO79-PEO20

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Surfactant-templated synthetic SiO2 mesoporous P123

• Well mesostructural ordering properties

• amphiphilic character

• low-cost

• commercial availability

• Biodegradability

• thick silica walls

PEO20-PPO70-PE020poly(ethylene oxide)-poly(propylene Oxide)- Poly(ethylene oxide)

organic structure-directing agents

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TiO2 synthesis by sol-gel method•Ti(OC3H7)4 + 4 H2O Ti(OH)4+ 4C3H7OH

•The high hydrolysis reactivity of TiO2 precursor, TTIP may cause uncontrolled local precipitation

•Acetic acid was added to control the hydrolysis speed

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Experimental ProcedureH2SO4

Aqueous solution

Na2SiO4 P123

Aging30C, 48 hr

Filtering &

Drying (60oC, 24hr)

Calcination600oC

SBA-15 mesoporous

TTIPAcetic acid C2H5OH

SBA-15mixing

Stiring&

Filtering

Drying

Calcination

TiO2/SBA-15

FTIR TEM XRD SAXS XPS UV-Visible N2 adsorption/desorption

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SBA-15

SBA powder: 2 m (length), 400 nm (diameter)

well-ordered hexagonal mesoporous silica structures, pore size = 6-7 nm

Wall thickness = 5 nmFFT

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SAXS of powder SBA-15

The calcined SBA-15 powder

Three resolved pe

aks (100), (110), (200)

Well-ordered hexagonal P6mm Structure

1 2 3 4 50

2000

4000

6000

8000

10000

Inte

nsity

2degree)

(100)

x5

(110)(200)

(h k l) d (Å)

(100) 95.9

(110) 55.1

(200) 47.8

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N2 adsorption/ desorption isothermsof SBA-15

•P/P0=0.68 – 0.75, Capillary condensation taking place in mesoporoes •Hysteresis loop, Type IV physisorption isotherms, => mesoporous structure•H1 type, uniform spheres in fairly regular array, narrow distributions of pore size.

desorption

0.0 0.2 0.4 0.6 0.8 1.0

100

150

200

250

300

350

400

450

500

N2 a

dso

rbe

d (

cm3 /g

,ST

P)

Relative Pressure(P/P0)

adsorption

Types of physisorption isotherms, IUPAC

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Pore size distribution

The synthesized SBA-15 with:

Uniform and narrow pore size distribution

Pore size: 6~7nm5 10 15 20 25 30

0

1

2

3

4

Po

re V

olu

me

(cm

3/g

)

Pore diameter(nm)

20 nm

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Pure TiO2

300 400 500 600 700 800

18

20

22

24

26

28

30

32

34

36

38

40

42

44

Gra

in s

ize(

nm)

Temperature (0C)

•XRD •Particle size

•TEM

Rutile

Anatase

20 30 40 50 60 70 80 90

8000C

7000C

6000C

5000C

4000C

3000Cuncalcined

Inte

nsi

ty

2

R

A

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XRD patterns of TiO2/SBA-15

20 30 40 50 60 70 80 90

Pure TiO2

80% TiO2

60% TiO2

30% TiO2

20% TiO2

Re

lativ

e In

ten

sity

2

R

A

TiO2/SBA-15 composites

calcined at 700oC

20 30 40 50 60 70 80 90

pure TiO2

80% TiO2

60% TiO2

30% TiO2

Rel

ativ

e In

tens

ity2

20% TiO2

R

A

TiO2/SBA-15 composites

calcined at 800oC

Anatase : all TiO2/SBA-15 composites Anatase :20%- 60% TiO2/SBA-15 A+R : 80% TiO2/SBA-15

•TiO2 grain size is decrease by supported on SBA-15•TiO2 Anatase -> Rutile transition temp. from 700 -> 800C

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SAXS spectra of TiO2/SBA-15

SBA-15 hexagonal structure still maintained after loading different amount of TiO2

Channels of SBA-15 may contain TiO2 particles

1.0 1.5 2.0 2.5 3.0

Rel

ativ

e In

tens

ity

2Theta/degree

1. SBA152. 20% TiO

2

3. 30% TiO2

4. 60% TiO2

1

2

3

4

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N2 adsorption/desorption isothermsof TiO2/SBA-15

2 4 6 8 10 12 140

1

2

3

4

Por

e vo

lum

e(cm

3/g

)

Pore size(nm)

20% TiO2/SBA-15

30% TiO2/SBA-15

60% TiO2/SBA-15

80% TiO2/SBA-15

SBA-15

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TiO2 contents vs. crystal size, pore size, pore volume

0 10 20 30 40 50 60 70 80 900

2

4

6

8

10

Por

e si

ze(n

m)

TiO2%

6000C

7000C

8000C

0 10 20 30 40 50 60 70 80 90

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Por

e V

olum

e(cm

3/g

.nm

)

TiO2%

6000C

7000C

8000C

0 10 20 30 40 50 60 70 80 900

50

100

150

200

250

300

350

400

450

500

550

600

650

700

S

peci

fic a

rea

SB

ET(c

m3/

g,S

TP

)

TiO2%

6000C

7000C

8000C

20 30 40 50 60 70 80 90 100 110

5

10

15

20

25

30

35

40

45

crys

tal s

ize

(nm

)

TiO2%

6000C

7000C

8000C

Crystalline size

Specific area

Pore size

Pore volume

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Pore shape evolution

SBA-15: H1 spherical shape

20-30 %TiO2/SBA: H1~ H2 type

60% TiO2/SBA: H2, ink bottle shape, some pores are seal with TiO2 particles

80% TiO2/SBA: H4, plate-like or slit shaped pores, pores are serious sealed with TiO2 particles

H4

H2

H1

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TiO2/SBA-15 composites

20% TiO2/SBA-15 30% TiO2/SBA-15 60% TiO2/SBA-15100 nm

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HRTEM

TiO2 nanoparticles are embedded in SBA-15 channel grain size ~ channel’s diameter

d spacing=0.357nm=>Anatase TiO2 (101)

100 nm

Ti

TEM cross-section image

EDS

DP

TiO2

SiO2

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FTIR spectra

1090 cm-1: Si-O-Si asymmetric stretching

470 cm-1: Si-O-Si bending mode 940 cm-1: Si-O-Ti vibration band TiO2 , peaks int.

Titanium incorporating into the framework of silica

1100 1000 900 800 700 600 500 400

80%TiO2

60%TiO2

30%TiO2

Tra

nsm

itta

nce

(%)

Wavenumber/cm-1

20%TiO2

pure SBA-15

Pure TiO2

1090cm-1470cm-1

940cm-1Si-O-Ti

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XPS 532.2 eV Si-O-Ti bonding:

chemical bonding occur between TiO2-SiO2

SBA-15: Si-O tetrahedral TiO2: Ti-O octahedral More complicated oxygen

coordination states appear in TiO2-SBA-15

Imply that Si-O-Ti would inhibited the phase transition from of anatase to rutile TiO2

518 520 522 524 526 528 530 532 534 536 538 540 542-200

0

200

400

600

800

1000

1200

Co

un

ts

Binding Energy(eV)

O1s:(TiO2-SiO

2) 1-533eV (Si-O-Si)

1

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2-532.2eV(Si-O-Ti)

3-529.7eV(Ti-O-Ti)

522 524 526 528 530 532 534 536 538 540

Binding Energy(eV)

O1s(529.7eV)

Pure TiO2

520 525 530 535 540 545

Binding Energy(eV)

533eV Si-O-Si

SiO2

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UV-Visible spectra

300 – 350 nm: TiO2 particle size < 5 nm 350- 400 nm: TiO2 particle size > 5 nm Absorption edge: blue shift calcined temp , absorption edge red shift

300 400 500 600 700 8000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Ab

sorb

an

ce

Wavelength (nm)

Pure TiO2

20% TiO2

30% TiO2

60% TiO2

600oCcalcined

300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0

Ab

sorb

an

ceWavelength(nm)

Pure TiO2

20% TiO2

30% TiO2

60% TiO2

800oCcalcined

[Ti3+-O-L]* [Ti4+-O2-

L]h

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TiO2/SBA-15 formation mechanism

SBA-15

+TTIP hydrolysis

TiO2 30 % TiO2 < 60 %T 700C

TiO2 > 60 %T > 800C

Amorphous TiO2

Anatase TiO2 Rutile TiO2

calcined

TiO2 temp

Ink-like pore slit shaped pores

spherical pore

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Standard calibration curve of Methylene Blue (MB)

0.000 0.001 0.002 0.003 0.004 0.0050.0

0.1

0.2

0.3

0.4

0.5

Ab

sorb

an

ce

Concentration

y = 81.576x

Beer’s Law:A ＝ b c

A:absorption:proportionconstant b: light lengthc: concentration

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Degradation of MB Langmuir-Hinshelwood ln(C/C0)=kt C0: initial concentration of Meth

ylene Blue k: rate constant

kTiO2 : 0.004 min-1 k30%TiO2 : 0.027 min-1

k60%TiO2: 0.023 min-1

30 % TiO2/SBA15 has the similar degradation rate with 60 %TiO2/SBA15

0 2 4 6 8 100.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

30%TiO2

60%TiO2

pure TiO2 (P-25)

without catalyst

C/C

O

Time(hr)

dark

0 2 4 6 8

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Conclusions High surface area (500 m2/g), high pore volume (0.55 cm3/g) of

TiO2 supported on SBA-15 composites have been obtain. (30 %TiO2/SBA-15 calcined at 700C)

Nanosized of 5 nm TiO2 particles embedded in the channel of the mesoporous silica structures.

The SBA-15 supported TiO2 increased the formation temperature of anatase phase to rutile phase from 700C to 800 C and inhibit the TiO2 grain growth by the occurs of Si-O-Ti bonding.

The pore shape from spherical change to plate-like or slit-shaped by increasing the TiO2 content higher than 30 % in the mesoporous silica structure.

Photocatalytic activity of SBA-15 supported TiO2 composite has 3 time increase than the commercial pure TiO2 nanopowder (P25)

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Thanks for your attention

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