Carbon nanotubes (CNTs) have attracted wide interest in many areas of science and technology since 1991 1, To optimize the use of CNTs in various applications, it is necessary to attach functional groups or other nanostruc-tures to their surface. The combination of CNTs with other nanocrystals is expected to be useful for applications in catalysts, sensors, nanoelectronic devices, data storage/ processing deA'ices, field emission displays, and polymer, or ceramic reinforcement 2. Several metal oxide nanoparti-cles, such as A1_2O_3 3, TiO_2 4, Eu_2O_3 5, etc., have been bound to the surfaces of CNTs. CeO_2 is a technologically important rare earth material because of its wide application as a catalyst in oxygen sensors and fuel cells and for the elimination of toxic auto-exhaust gases. The hybrid of CNTs and CeO_2 shows exceptional adsorption capacity and catalytic properties, and has the potential to be widely used in the above-mentioned catalytic field. Ding et al. 6,7 reported that CNTs refiuxed in a mixture of concentrated nitric and sulfuric acids at 140 deg C could be coated with CeO_2. However, only a few studies have been reported on the fabrication of CNT/CeO_2 composites. Therefore, the preparation of CNT/CeO_2 composites still remains challenging. No reports on the synthesis of CNT/CeO_2 composites without any chemical modification of CNTs or any assisted surfactant have been published to date. Here we report the first synthesis of CNT/CeO_2 composites in a large scale by a simple ultrasonication method under ambient air.
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