The formation of monodisperse, tunable sized, alloyed nanoparticles of Ni, Co, or Fe with Pt and pure Pt nanoparticles attached to carbon nanotubes has been investigated. Following homogeneous nucleation, nanoparticles attach directly to non-functionalized singlewall and multiwall carbon nanotubes during nanoparticle synthesis as a function of ligand nature and the nanoparticle work function. These ligands do not only provide a way to tune the chemical composition, size and shape of the nanoparticles but also control a strong reversible interaction with carbon nanotubes and permit controlling the nanoparticle coverage. Raman spectroscopy reveals that the sp2 hybridization of the carbon lattice is not modified by the attachment. In order to better understand the interaction between the directly attached nanoparticles and the non-functionalized carbon nanotubes we employed first-principles calculations on model systems of small Pt clusters and both zig-zag and armchair singlewall carbon nanotubes. The detailed comprehension of such systems is of major importance since they find applications in catalysis and energy storage.Composites of metallic nanoparticles (NPs) and carbon nanotubes (CNTs) exhibit high catalytic activity for various chemical reactions [1][2][3][4][5][6] and have also been explored for hydrogen storage applications [7]. Recent reports include platinum [6,8,9] [19,20] and catalytic properties [21][22][23]. Beyond that, 1D alignment of NPs enables to modify the saturation magnetization and coercitivity through magnetostatic coupling [24][25][26]. A convenient way for 1D alignment is the attachment of NPs to CNTs, which is usually achieved by electrochemical deposition [27,28], the reduction of metallic salts in the presence of functionalized CNTs [15,29], or chemical vapor deposition [10], among others [30]. On the other hand, concerning the NP synthesis, the organometallic synthesis route provides nanocrystalline alloyed materials with precise size control and tunable composition in several systems [20,31,32]. Here, we report on the synthesis of alloyed N i x P t 1−x [20], Co x P t 1−x and F e x P t 1−x [32] NPs as well as pure P t [33] NPs and their attachment to non-functionalized singlewall (SWCNTs), multiwall carbon nanotubes (MWCNTs) and glassy carbon by their simple integration in the organometallic synthesis. The experimental procedure involves only a single synthetic step, whereby the crucial parameter for attachment was found in the correct balance of the ligands oleylamine (OA) and oleic acid (Oac).

The frictional properties of individual carbon nanotubes (CNTs) are studied by sliding an atomic force microscopy tip across and along its principle axis. This direction-dependent frictional behavior is found to correlate strongly with the presence of structural defects, surface chemistry, and CNT chirality. This study shows that it is experimentally possible to tune the frictional/adhesion properties of a CNT by controlling the CNT structure and surface chemistry, as well as use friction force to predict its structural and chemical properties.

Although monolithic catalysts offer distinct advantages such as low pressure drops and easy catalyst separation compared to tube bundle reactors filled with pellets and are for instance widely used for automobile exhaust treatment, the coating of the monolithic structures with the catalytically active phase is often complex and recipes need to be established empirically. In contrast to traditional methods, such as dip-coating or impregnation of the monolith, where the active nanoparticles are formed during the preparation on an oxidic washcoat usually used and deposited simultaneously or in a previous step, we demonstrate in this study that alternatively preformed colloidally synthesized nanoparticles can be employed to obtain homogeneous coatings with or without a washcoat. In this way, one can take advantage of the far-reaching possibilities of colloidal methods to control the structure and size of the nanoparticles and also to tune and optimize their binding to the monolithic surface. For cases where beneficial metal-support interactions between the nanoparticles and a washcoat improve the catalytic properties we demonstrate that colloidally prepared nanoparticles can be directly mixed with a washcoat slurry and successfully deposited on monolithic supports. Turnover frequencies comparable to the corresponding powder catalysts could be reached. In a second approach, we present here a facile method to directly coat three different monolithic supports (cordierite honeycomb, Al 2 O 3 foam and Nickel fleece) with preformed Pt nanoparticles in the presence and absence of organic ligands. In order to realize high metal loadings, the beneficial influence of a ligand ''double-layer'' (coating of nanoparticles and the support by organic ligands) enhancing the adhesion between the Pt nanoparticles and the underlying monolithic support will be discussed. In the case of the metallic Ni substrate, this approach furthermore allows to circumvent alloy formation and nanoparticle diffusion into the metallic substrate. This can greatly increase long-term stability of systems coated directly onto metallic substrates without an additional oxidic washcoat.

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