1 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 , Republic of Korea b Research Center, TIOZ Co. Ltd., Wonsi-dong, Ansan, Kyunggi-Do, Republic of Korea c Division of Materials Chemistry, Royal Institute of Technology, SE 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

2 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.

3 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.

4 Introduction (3/3)  TiO 2 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.

5 Experimental drugs Titanium isopropoxide ( 異丙氧基鈦 ) (Ti[OCH(CH 3 ) 2 ] 4 ) (precursor) Isopropyl alcohol (solvent) AcAc:Acetylacetonate ( 乙醯丙酮 ) (chelating agent) HNO 3

6 Experimental procedure TIP H 2 O + HNO 3 dropping Stirring (90 min.) TiO 2 sol with AcAc TIP + IPA Stirring (10 min.) H 2 O + HNO 3 Dropping (30 min.) Stirring (80 ℃, 8hr) TiO 2 sol without AcAc Stirring (30 min.) IPA + AcAc

7 Results and Discussion 3400cm cm cm cm -1

8 XRD pattern : without AcAc

9 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 ℃. 10

11 Photocatalytic decomposition rate

12 Comparison of photocatalytic decomposition rates (1/2)

13 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.

14 Surface roughness

Structure  The hydrolysis between alkoxides and H 2 O is incomplete. → The monomers of (OH) x -Ti(OR) 4 −x form chain-like structures.  The hydrolysis between alkoxides and H 2 O is complete. → the monomers of (OH) x -Ti(OR) 4 −x interact with each other to establish a three-dimensional network structure. 15

Conclusion  TiO 2 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 to 3.08 nm and from 3.72 to 5.35 nm for the TiO 2 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. 16

Thanks for your attention 17