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Effect of Calcination Temperature and Addition of Silica, Zirconia, Alumina on the Photocatalytic Activity of Titania Kyeong Youl Jung and Seung Bin Park ~ Department of Chemical Engineering, Korea Advanced institute of Science and Technology, 373-1, Kusong-dong Yusong-gu, Daejeon 305-701, Korea (Received 3 September 2001 9 accepted 15 October 2001)

Abstraet-Nanophase titania was prepared by ~)l-gel method and spray pyrolysis. We tried to elucidate the relationship between the pN~tt~activity and the crystallite size of anatase phase, I-o better understand the changes in the bulk and the surlhce of titania a~ the calcination temperature is changed. EPR and ph~toluminescence analysis were carried out. The effect of the secondar?' metal oxide embedded into titania matrix on the photoactMty was also im,'estigated. It was lbund that the photoacti~,ity of titania has a linear relationship to the c~,stallitc size. For the analysis of EPR and phototuminescence Ibr pure titania, the incm&se of photoactivity with increasing the calcination temperature is due m the tbrm~ion of surlhee active sites such as O as well as the increase ofcls~stallini~' resulting fi'om the rcmm, al of bulk defects, l:or silica/titania mixed oxide, it was found that the improvement of the thermal stability of anatase pha~ is important to enhance the phottJactMty of titania because the prepared catalyst wa~s calcined at a higher temperature than 700 "C without lbrming mtile phase. It was also concluded that the simultaneous increase of the surtZace area and the c~5,stallinity promises m improve the photoactivi~; achieved by' increasing the content of silica up to 60%. By the analysis of EPR and photoluminescence, it was ~bund that the embedNng of silica into titania matrix supwesses the tbrmation of Ti -*- and produces a new active site of Ti-O-Si, which easily interacts with the oxygen, In the investigation of zfl'conia/titania and alumina/titania mixed oxide, it was found that the increase of the surface OI t is essential to l~sitively affect of the imN'oved thermal stability on the photoaetivity. Key words: Titania, Sol-Gel Method, Mixed Oxide. EPR. Phot~Iuminescence

such as sol-gel synthesis, the post heat treatment temperature is crucial to the photoactivity because it changes the crystallinity as well as the crystal structure offit~ania~ 1ligher crystallinity needs higher calcination temperature. But, the increase of calcination temperature to improve the crystallinity of titania prepared by a liquid phase technique is limited because anatase phase is thermally unstable and turned into futile phase which is less photoactive. "I]ms the major goal of this work is to improve the thermal stability of titania for the phase transition. The use of mixed oxide or multicomponent oxide as a photocatalyst is a novel class in recenl years. ~fhe key concept for the modification of titanium oxide with other oxides such as Fe:_O~, SiO_,, ZrO2, AI,(L, N~O,, WO~, and MoO, is to change the surface or structural properties and the photochemical property to impr