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Photocatalytic behavior of TiO2 thin films prepared by sol–gel process

Ki Hyun Yoon a,b,c, , Jung Sok Noha, Chul Han Kwon a,b, Mamoun Muhammedc∗a Department of Ceramic Engineering, Yonsei University, 134 Shinchon-dong, Seodaemoon-ku, Seoul 120-749, Republic of Korea

b Research Center, TIOZ Co. Ltd., 775-4 Wonsi-dong, Ansan, Kyunggi-Do, Republic of Koreac Division of Materials Chemistry, Royal Institute of Technology, SE-10044 Stockholm, Sweden

Received 24 December 2004; received in revised form 23 May 2005; accepted 1 June 2005

報告學生：周暐祥報告日期： 2009/12/02

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Introduction (1/3)

Titania has been widely used and explored as a photocatalytic material since it is nontoxic, chemical stable, inexpensive, and has favorable optoelectronic property.

Titanium dioxide possesses three different crystal structures: rutile (tetragonal), anatase (tetragonal) and brookite (orthorhombic).

The advantages of the sol–gel method are: good homogeneity, ease of composition control, and low processing temperature, and films are easily anchored on the substrate.

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Introduction (2/3)

The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly.

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Introduction (3/3)

TiO2 solutions were prepared using alkoxide sol–gel process with and without AcAc and their physical and chemical properties were investigated.

The thin films using these two different solutions were spin-coated on the glass substrates and their comparison was made in terms of the photocatalytic decomposition rate using methylene blue solution.

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Experimental drugs Titanium isopropoxide ( 異丙氧基鈦 ) (Ti[OCH(CH3)2]4) (precursor)

Isopropyl alcohol (solvent)

AcAc:Acetylacetonate ( 乙醯丙酮 ) (chelating agent)

HNO3

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Experimental procedure

TIP

H2O + HNO3 dropping

Stirring (90 min.)

TiO2 sol with AcAc

TIP + IPA

Stirring (10 min.)

H2O + HNO3 Dropping (30 min.)

Stirring (80 , 8hr)℃

TiO2 sol without AcAc

Stirring (30 min.)

IPA + AcAc

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Results and Discussion

3400cm-1

1640cm-1

1380cm-1

500cm-1

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XRD pattern : without AcAc

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XRD pattern : with AcAc

Resultant of XRD

The addition of AcAc as a chelating agent to titanium isopropoxide leads to much less reactive titanium(acetylacetonate).

During heat treatment, pyrolysis may induce the formation of the metastable anatase phase and converts the anatase phase to the rutile phase at 500 .℃

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Photocatalytic decomposition rate

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Comparison of photocatalytic decomposition

rates (1/2)

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Comparison of photocatalytic decomposition rates

(2/2) Upon illumination of UV light for 120 min, the photocatalytic

decomposition rate of the specimen without using AcAc exceeded that of the specimen using AcAc by 10 %.

This difference can be explained in terms of the surface area.

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Surface roughness

Structure

The hydrolysis between alkoxides and H2O is incomplete.

→ The monomers of (OH)x-Ti(OR)4−x form chain-like structures.

The hydrolysis between alkoxides and H2O is complete.

→ the monomers of (OH)x-Ti(OR)4−x interact with each other to establish a three-dimensional network structure.

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Conclusion TiO2 thin films prepared using AcAc showed the anatase

phase at 300 while the anatase phase from the TiO℃ 2 thin films prepared without using AcAc began to form at 100 .℃

Surface roughness ranged from 0.414 to 3.08 nm and from 3.72 to 5.35 nm for the TiO2 thin films with and without using AcAc, respectively.

The photocatalytic decomposition activity exhibited a close dependence on the formation of the anatase phase and the surface roughness.

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Thanks for your attention

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