In situ growth of Au@CeO2 core–shell nanoparticles and CeO2nanotubes from Ce(OH)CO3 nanorods

Abstract

Core–shell (CS) nanoparticles (NPs) have many applications in areas such as catalysis and sensing. The utilization of hollow nanostructured materials as the supports, such as nanotubes (NT), is a growing interest to anchor NPs. Generally, several steps are necessary to prepare CS NP–NT nanocomposites, including: (i) the synthesis of CS NPs; (ii) the preparation of NTs; and (iii) the combination of CS NPs and NTs. Moreover, surface modifications with organic ligands are often involved during the synthesis of CS NPs and/or the step combining CS NPs and supports. Here we report a facile method for in situ growth of Au@CeO₂ CS NPs and CeO₂ NTs by mixing HAuCl₄ and Ce(OH)CO₃ nanorods under mild conditions. The formation of Au–CeO₂ nanocomposite is due to the interfacial oxidation–reduction reaction between HAuCl₄ and Ce(OH)CO₃, where Au(III) in HAuCl₄ is reduced to Au(0) by Ce(III) in Ce(OH)CO₃, while Ce(III) is oxidized into Ce(IV), followed by hydrolysis to generate CeO₂. The slow hydrolysis rate of Ce(IV) leads to the coverage of CeO₂ on the Au NPs, and on the residual Ce(OH)CO₃ surface, developing into Au@CeO₂ and Ce(OH)CO₃@CeO₂ CS structures. Further depletion/dissolution of Ce(OH)CO₃ results in Au@CeO₂ CS NP–CeO₂ NT nanocomposite eventually. The advantages of our synthetic strategy are independent of foreign reducing agents and additional surface modification. And, such CS NP–NT nanocomposite can be obtained in one step, simplifying the synthesis procedures greatly. This method based on interfacial oxidation–reduction may be employed as a unique entry to other nanocomposites.