Effect of precursors on the morphology and the photocatalytic water-splitting activity of layered perovskite La 2 Ti 2 O
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Effect of Precursors on the Morphology and the Photocatalytic Water-Splitting Activity of Layered Perovskite LazTi~O~ Jindo Kim, Dong Won Hwang, Sang Won Bae, $bung Gul Kim and Jae Sung Lee* Research Center for Catalytic Technology (RCCT), Department of Chemical Engineering, School of Environmental Science & Engineering, Pohang University of Science and Technology (POSTECH), San 31 Hyoja-Dong, Pohang 790-784, Korea (Receh'ed 17 September 2001 9 accepted 5 October 200I)
Abstract-A [110] layered perovs!dte, La,Ti,Or, was a good photocatalyst under ultraviolet light in water splihing reaction. The material was synthesized with La,O~ and TiQ, as precursors by solid-state tl-oz~sformation. The morphology and photocatalytic activity of La,Ti,O~ depended on the preparation methods, as well as purity and morphology of the precursors. Wet-grincling of precursors in ethanol gave a product with higher crystallinity and phase pmity, and thus higher photocatalytic activity, than dly-grinding without solvent. It was important to reduce the particle size of LabOr, as it usually had larger initial particle sizes than TiO> Thus, the particle size of L~O~ had a strong effect on the crystallinity and surface area of the product La,Ti,O> On the other hand~ a severe chemical purity control was required for TiO,, while the effect of morphology was relatively small. In all cases, a high degree of crystallinity and purity of the prepared L a,Ti~O~ was critical to show a high photocatalytic water-splitting activity. Key words: Layered Perovs!dte, Photocatalyst, Water Splitting, La,Ti,O~, Precursor
INTRODUCTION
ll)~ [Domen et al., 1986]. These layered materials use their interlayer space as reaction sites, where electron-hole recombination process could be retarded by physical separation of electron and hole pairs generated by photo-absorption. The present investigators also found novel photocatalysts, (110) layered perovs!dte materials [Schmalle et al., 1993; Ishizawa et al., 1982; Balachandran and Eror, 1989], which showed much-improved photon yields as high as 23~ [KJrn et al., 1999]. The materials are a series of homologous s ~ c tnres with a generic Comlmsition of A_~,B~,O3~,+~(m=4, 5; A=Ca~ Sr, La; B=Nb, Ti). Fig. 1 shows the schematic feature of the layered struc~are of La~Ti~O7 [Williams et al., 1991], a member of (110) layered perovskite materials with m=4. The layers are parallel to (110) planes of perovs!dte slructure. At the moment, photon yields as high as 3(~o under UV light have been relmrted for this type of semiconductor photocatalyst. our study of these materials, it has been observed that performance of the photocatalysts varies widely with the catalyst
Photocatalytic water splitting directly produces clean and high energy-containing H~ in a CQ,-neu~al manner from abundant H~O using solar energy. If successfully developed with economic viability, this could be the ultimate technology that could solve fi,a~e energy and environmental problems. The possibility of solar energy harvesting using semiconductor-based photoele
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