Magnetic and microstructural analysis of palladium nanoparticles with different capping systems

Abstract

Palladium nanoparticles capped with different protective systems in a size range between 1.2 and 2.4 nm have been obtained by varying the preparation chemical method. Magnetization curves for all the samples show hysteresis loops, evidencing a ferromagnetic or a permanent magnetism in the nanoparticles. The microstructure of the nanoparticles has been analyzed by x-ray absorption and transmission electron microscopy. The nature of the magnetic behavior found for all these Pd nanoparticles ͑NPs͒ is different depending on their sizes and structural features and is explained on the basis of two different suggested mechanisms. The particles protected by means of a surfactant ͑tetralkylammonium salts͒, present a ferromagnetic order related to the factors increasing the density of states just below the Fermi level. Whereas, when the nanoparticles are stabilized by covalent bonds with protective species ͑thiol derivatized alkane chains or surface oxidized Pd NPs͒, the increase of the 4d density of holes, localized by the bonded atoms ͑S or O͒, is giving rise to the observed ferromagneticlike behavior.

Unexpected magnetism in gold nanostructures: making gold even more attractive

“…One of the more surprising recent incarnations of such novel magnetic behavior is the observation of magnetic properties in nanoscaled materials which are diamagnetic (i.e., nonmagnetic) in the bulk. This type of behavior has been observed in metal oxide nanoparticles and nanocrystalline films [16,17], as well as typically paramagnetic (e.g., Pd [18][19][20][21][22][23]) and diamagnetic (Cu, Ag, Pt [24,25]) metal nanostructures. The latter include gold-based nanostructures, which will be the topic of this review.…”

Electronic structure, magnetic properties, and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

“…Particularly, the magnetic properties of clusters of 4d elements, which are non-magnetic as bulk materials, have attracted much of the attention (e.g. Kumar and Kawazoe, 2003;Shinohara et al, 2003;Sampedro et al, 2003;Litrán et al, 2006;Hernando et al, 2006c); among these 4d transition metals, gold has been the target of many investigations either as thin films with or without an organic layer on top (Carmeli et al, 2003;Reich et al, 2006), or as nanometric particles with our without capping molecules (Hori et al, 1999;Crespo et al, 2004). Despite all the efforts in this field, the permanent magnetism shown by these systems is not yet understood (Vager and Naaman, 2004;Hernando and García, 2006;Hernando et al, 2006a;Crespo et al, 2006).…”

Solid‐State Electrochemical Method for Determining Core and Shell Size in Pd@PdO Nanoparticles

“…Here, the characteristic 3d 5/2 and 3d 3/2 peaks for Pd(0) at 333.8 and 339.2 eV, respectively, and also the corresponding peaks for Pd(II) at 335.9 and 341.4 eV appear. These results suggest that a significant part of the palladium is oxidized to palladium oxide, probably, as described by Litran et al [12], during the step of palladium nanoparticle formation, generating a small oxide shell surrounding the metal cluster. However, the presence of Pd 2þ (and Pd 4þ ) accompanying Pd(0) in XPS can also be attributed to electron deficiency in small Pd nanoparticles [40 -42].…”

“…In liquid media, organic ligands are typically used as capping agents for the synthesis of MNPs, because they are able to efficiently control the nanoparticle size by joining their surface. For those kind of organic agents, two different types of interactions are reported [12], i) strong interactions due to covalent bonding, and, ii) weak interactions produced by labile dipole molecules which interact with MNPs by means of electrostatic forces. The main advantage of this last nanostructure is the possibility to easily exchange the capping, enabling to transfer the MNP from organic to water media and vice versa [13].…”

“…The core/shell metal@metal oxide nanoparticles so generated have been subject of special interest, due to their significant characteristic properties, for instance, better catalytic ability with regard selected chemical processes, depending on the nature of oxide coatings [14 -16]. It has be reported [12] that this method allows for obtaining tetraalkylammonium-capped nanoparticles formed by a Pd core surrounded by a shell of PdO (labeled in the following as Pd@PdO), which contrast with those obtained when using a ligand strongly bound to the metal core through thiol groups or similar (see Scheme 1).…”