Nano Res. 2011, 4(12): 1233– 1241 1233 One-Step Synthesis of Magnetically Recyclable Au/Co/Fe Triple- Layered Core–Shell Nanoparticles as Highly Efficient Catalysts for the Hydrolytic Dehydrogenation of Ammonia Borane Kengo Aranishi 1,2 , Hai-Long Jiang 1 , Tomoki Akita 1,4 , Masatake Haruta 3,4 , and Qiang Xu 1,2,4 (  ) 1 National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan 2 Graduate School of Engineering, Kobe University, Nada Ku, Kobe, Hyogo 657-8501, Japan 3 Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Minami-Osawa, Hachioji, Tokyo 192-0397, Japan 4 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan Received: 23 March 2011 / Revised: 13 August 2011 / Accepted: 1 September 2011 © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2011 ABSTRACT Magnetically recyclable Au/Co/Fe core–shell nanoparticles (NPs) have been successfully synthesized via a one-step in situ procedure. Transmission electron microscope (TEM), energy dispersive X-ray spectroscopic (EDS), and electron energy-loss spectroscopic (EELS) measurements revealed that the trimetallic Au/Co/Fe NPs have a triple-layered core–shell structure composed of a Au core, a Co-rich inter-layer, and a Fe-rich shell. The Au/Co/Fe core–shell NPs exhibit much higher catalytic activities for hydrolytic dehydrogenation of ammonia borane (NH 3 BH 3 , AB) than the monometallic (Au, Co, Fe) or bimetallic (AuCo, AuFe, CoFe) counterparts. KEYWORDS Triple-layered, core–shell nanoparticles, heterogeneous catalysis, ammonia borane, hydrogen generation 1. Introduction Heterometallic nanoparticles (NPs) have attracted growing attention in recent years owing to their unique and novel properties, which are often very different from those of the monometallic counterparts [1–16]. The incorporation of magnetic elements in NPs will expand their applications to biomedical operations, information storage, and heterogeneous catalysis [15, 16]. Therefore, studies of the synthesis and applications of magnetic alloy NPs are of great interest in terms of seeking synergistic structural and electronic effects combined with the intrinsic pro- perties of the magnetic element. There have been a considerable number of investigations of core–shell structured bimetallic magnetic NPs [16–18], whereas magnetic core–shell NPs with a triple-layered structure are, to the best of our knowledge, rare [18–20]. Triple-layered trimetallic NPs might have superior physicochemical (especially catalytic) performances to their monometallic/bimetallic counterparts because their electronic structures are more tunable [6, 21]. Toshima and coworkers have fabricated ~3 nm Au/Pt/Rh trimetallic NPs by simple mixing of bimetallic Au/Pt NPs and monometallic Rh NPs [18]. Sun and coworkers have obtained ~6 nm Pd/Au/FePt core–shell NPs via a multi-step synthetic approach [19]. Yamauchi and coworkers have reported the one-step synthesis Nano Res. 2011, 4(12): 1233– 1241 ISSN 1998-0124 DOI 10.1007/s12274-011-0174-1 CN 11-5974/O4 Research Article Address correspondence to q.xu@aist.go.jp