Decorating Titanate Nanotubes with CeO 2 Nanoparticles Bartolomeu C. Viana, †,| Odair P. Ferreira, ‡ Antonio G. Souza Filho,* ,†,‡ Carolina M. Rodrigues, ‡ Sandra G. Moraes, § Josue Mendes Filho, † and Oswaldo L. Alves* ,‡ Departamento de Fı ´sica, UniVersidade Federal do Ceara ´ s UFC, P.O. Box 6030, 60455-900, Fortaleza-CE, Brazil, Laborato ´rio de Quı ´mica do Estado So ´lido - LQES, Instituto de Quı ´mica, UniVersidade Estadual de Campinas s UNICAMP, P.O. Box 6154, 13083-970, Campinas-SP, Brazil, Laborato ´rio de Energia e Meio Ambiente, UniVersidade Metodista de Piracicaba s UNIMEP, RodoVia SP 306 - km 24, 13450-000, Santa Ba ´rbara; d’Oeste-SP, Brazil, and Departamento de Fı ´sica, UniVersidade Federal do Piauı ´ s UFPI, 64049-550, Teresina-PI, Brazil ReceiVed: July 18, 2009; ReVised Manuscript ReceiVed: October 1, 2009 In this work, we report the synthesis, characterization, and application of Ce ion-exchanged titanate nanotubes (Ce-TiNTs). The physicochemical properties of these Ce-TiNTs are discussed in comparison with their pure titanate nanotube counterparts. The transmission electron microscope images showed that the Ce-TiNTs have the same morphology as that of pristine nanotubes and their external walls are decorated with cerium oxide nanoparticles. The mechanism of nanoparticle formation is based on the precipitation of Ce ions at the nanotube surface. We observed a red shift of the absorption band edge toward the visible region whose main contribution comes from the Ce ion intercalation. A red shift of vibrational modes associated with metal ion-oxygen interaction was observed and identified as being due to the effect of Ce addition to the lattice as well as the anchoring of CeO 2 nanoparticles to the nanotube wall. We show that this hybrid system is promising for applications in photocatalysis using the blue region of the electromagnetic spectrum. This was demonstrated for photodegradation of Reactive Blue 19 textile dye. 1. Introduction Many technological applications that make use of the energy available in the sunlight have been gaining importance because this energy is free and also environmentally friendly. The correct choice of materials with suitable properties for using this clean energy is a key point for transforming the promising potential into real world technology, and band gap engineering is an approach used for achieving this goal. Combining the size- dependent properties of nanomaterials, such as the tunability of the band gap toward the visible range and their large surface- to-volume ratio, opens up the opportunity for developing a new generation of very efficient materials for photocatalysis and related applications. TiO 2 -based materials have been intensively investigated because their physical and chemical properties are suitable for important applications in solar cells, gas sensors, photocatalysis, and other environmentally related applications. 1-7 In particular, one-dimensional or elongated TiO 2 -based nanostructures, such as nanotubes and nanoribbons, exhibit improved properties different from their bulk counterparts, and therefore, they have a great potential for many applications, especially for photocatal- ysis. 2,8 Their elongated morphology allows the lifetime of photogenerated carriers to be extended relative to other TiO 2 - based materials. 9 Titanate nanotubes have a large surface area responsible for increasing the active surface. 10,11 They have also been tested for using as catalysts in heterogeneous photocatalysis and have shown excellent performance for degrading textile dyes, which makes these titanate nanomaterials very important ecomaterials. 12,13 However, the absorption band edge of titanate nanotubes is below 400 nm, 14 which makes them not very efficient for converting the free available photon energy from the sun in the visible range. Therefore, band gap engineering of titanate nanotubes, which consists of performing chemical modifications for shifting the absorption band edge of titanate nanotubes toward the visible range, is an important issue to be addressed in the search for the nanomaterials that would make efficient photocatalysts. The optical properties of sodium titanate nano- tubes may be effectively modified and controlled via ion- exchange reactions or intercalation of other metals. Furthermore, the presence of Na + in the lattice decreases the photocatalytic activity of TiO 2 because they are efficient recombination centers. 15 Therefore, submitting the titanate nanotubes to ion- exchange reactions involving some transition metals is impor- tant, and the literature has reported that the absorption band edge experiences a red shift toward the visible range. 16-18 These exciting results make the intercalated/modified titanate nanotubes promising systems for photocatalysis. To the best of our knowledge, there are no investigations on Ce ion-intercalated titanate nanotubes. On the other hand, ceria has attracted much attention due to its technological applications as an active catalyst, as a polishing agent, for sunscreens, for use in solid oxide fuel cells, 19,20 as an electrode material for gas sensors, silicon-on-insulator structures, 21 and high-T c su- perconductors, 20 among others. The catalytic properties of ceria can also be increased when prepared as nanoparticles with high surface-to-volume ratios. 22,23 In this paper, we present the synthesis and characterization of titanate nanotubes with Ce ions incorporated in the nanotube * To whom correspondence should be addressed. Phone: +55 35213147. Fax: +55 35213023. E-mail: agsf@fisica.ufc.br (A.G.S.F.), oalves@iqm.unicamp.br (O.L.A.). † Universidade Federal do Ceara ´ s UFC. ‡ Universidade Estadual de Campinas s UNICAMP. § Universidade Metodista de Piracicaba s UNIMEP. | Universidade Federal do Piauı ´ s UFPI. J. Phys. Chem. C 2009, 113, 20234–20239 20234 10.1021/jp9068043 CCC: $40.75  2009 American Chemical Society Published on Web 10/26/2009