Rodrigo Segura del Río Non-covalent assembly of hybrid nanostructures of gold and palladium nanoparticles with carbon nanotubes Hybrid nanostructures were prepared by mixing gold and palladium nanoparticles with multi- and single-walled car- bon nanotubes. The approach to prepare these nanohybrid implies the interaction of long hydrocarbon chains chemi- sorbed at the nanoparticles surface and the graphitic walls of nanotubes. Transmission electron microscopy results show the efficiency of this simple method to assemble these nanostructures. The electron microscopy images show that nanoparticles are effectively absorbed on the nanotube sur- faces homogeneously but without any particular order. These nanostructures have proven to be stable after a mod- erate ultrasonic treatment. Keywords: Hybrid nanostructures; Nanotubes; Nanoparti- cles; Gold; Palladium 1. Introduction The design of multifunctional nanostructures has attracted the imagination and efforts of many researchers in the last few years. Combining two (or more) types of materials, such as nanotubes and nanoparticles, might add new func- tionalities or extend the practical applications of these nano-objects. Carbon nanotubes (CNTs) are extremely re- sistant to mechanical tension, are highly flexible and can exhibit semiconducting, metallic or even superconducting properties [1, 2]. In short, they are the ideal building blocks for molecular nanoelectronics and at the same time very strong materials, which have already been incorporated into light reinforced composites [3]. On the other hand, noble metal nanostructures, such as gold or palladium nanoparti- cles (AuNPs and PdNPs), are of general interest mainly due to their remarkably high catalytic activity and their spe- cial electronic and optical properties. The technological perspectives of the hybrid structures formed by these kinds of materials in fields such as catalysis [4, 5], gas sensing [6, 7], electrochemical sensing [8, 9] and solar energy con- version [10] have attracted a widespread interest in the scientific community. Several groups have successfully synthesized hybrids of AuNPs on the surface of CNTs. They have mostly used covalent linkage through bifunctional molecules [11 – 13], while others have prepared hybrids taking advantage of electrostatic interaction between a polyelectrolite layer ab- sorbed in the nanotube wall and charged gold nanoparticles [14]. Other reports include the use of functionalized poly- cyclic aromatic hydrocarbons as non-covalent interlinker between gold nanoparticles and nanotubes [15]. Our group has also reported the synthesis of Au – CNT hybrid struc- tures by using a covalent route in which AuNPs anchor the CNT surface and after a thermal treatment they are encap- sulated by the carbon [16]. These new Au – CNT structures could be employed in optoelectronic devices as well as in biomedicine, allowing the possibility to carry and selectively deliver into the body different therapeutic drugs [17], or by using them in combi- nation with electromagnetic irradiation to provoke local- ized heating which could eventually destroy surrounding cancer cells [18]. On the other hand, Pd – CNT hybrids have been less ex- plored than the Au – CNT system. The few reports dealing with the synthesis of Pd – CNT hybrid nanostructures in- clude approaches such as the electrochemical deposition [19, 20] and wet chemical reduction [21 – 23] of Pd ions. Other metals have also been used to synthesize hybrids with CNTs. For example, AgNPs have been electro-crystal- lized onto functional multi-walled carbon nanotubes sur- faces [24]. The resulting nanohybrids show a high catalytic activity to the electro-oxidation of hydrazine. Magnetic iron [25], cobalt [26], and nickel [27] NPs have also been linked to CNTs to form hybrid structures. The use of these hybrids in magnetic storage as well as in nuclear magnetic reso- nance, as contrast agents for imaging and diagnosis, has been considered [28]. Other metals such as Pt [29], Rh [30], and Ru [31] have also been incorporated into CNTs mainly with the purpose of using them as catalysts or gas sensors. In this contribution we will present results of the synth- esis and characterization of hybrid nanostructures com- posed by palladium or gold nanoparticles and carbon nano- tubes by using a simple non-covalent synthetic route. 2. Experimental 2.1. Nanotube growth and purification MWCNTs were synthesized by chemical vapor deposition (CVD), through the decomposition of acetylene at 800 8C over a Pd/c-Al 2 O 3 catalyst [32]. The raw MWCNTs were purified by standard air oxidation, alkali and acid treat- ments [33, 34] to eliminate amorphous carbon, alumina, and the catalytic particles. The commercially available sin- R. S. del Río: Non-covalent assembly of hybrid nanostructures of gold and palladium nanoparticles Int. J. Mat. Res. (formerly Z. Metallkd.) 103 (2012) 7 901 Departamento de Química y Bioquímica, Universidad de Valparaíso, Valparaíso, Chile  2012 Carl Hanser Verlag, Munich, Germany www.ijmr.de Not for use in internet or intranet sites. Not for electronic distribution.