4 research outputs found
Nanostructure and Surface Composition of Pt and Ru Binary Catalysts on Polyaniline-Functionalized Carbon Nanotubes
PtâRu binary catalysts were prepared on a polyaniline-functionalized multiwalled carbon nanotube (PANi/MWCNT). PANi/MWCNT composites were synthesized by the polymerization of aniline in the presence of a carbon nanotube suspension using FeSO<sub>4</sub> and (NH<sub>4</sub>)<sub>2</sub>S<sub>2</sub>O<sub>8</sub> as the oxidants. The PtâRu/PANi/MWCNT catalysts were formed by the chemical reduction of H<sub>2</sub>PtCl<sub>6</sub> and RuCl<sub>3</sub> using NaBH<sub>4</sub> as the reducing agent. The binary component catalyst is sharply distributed, with particle sizes ranging from 2.0 to 4.0 nm, and the Pt and Ru distributions are homogeneous when supported on PANi/MWCNT. In comparison, the binary catalyst supported on bare MWCNT displayed a Pt-rich core and a Ru-rich shell nanostructure. The surface composition deduced from CO stripping potentials confirms that the Ru surface content (Ï<sub>Ru</sub>) is approximately 50% for the PtâRu alloy on PANi/MWCNT, and the catalyst on bare MWCNT shows nearly 70% Ru on the surface. PtâRu binary catalysts supported on PANi/MWCNT have higher activity, a higher Pt utilization efficiency, and much better durability when compared to other catalyst supports on bare MWCNT or on Vulcan XC-72
Spectroelectrochemical Probing of the Strong Interaction between Platinum Nanoparticles and Graphitic Domains of Carbon
This study focuses on clarifying
the strong interaction existing
between extended graphitic domains of ordered carbonaceous materials
such as multiwalled carbon nanotubes and platinum nanoparticles. This
interaction results from the heterogeneous nucleation of platinum
nanoparticles onto the carbon support. The metal clusters are chemically
synthesized by using the carbonyl route. Two different carbon supports
are used namely, homemade multiwalled carbon nanotubes, MWCNT-m, and
classical Vulcan XC-72. Physicochemical properties of these materials
are described by Raman spectroscopy, X-ray photoelectron spectroscopy
(XPS), and X-ray diffraction (XRD). The effect of the strong interaction
on the electronic properties of platinum nanoparticles is electrochemically
probed by means of CO stripping experiments coupled with <i>in
situ</i> Fourier transform infrared spectroscopy (FTIR). Density
functional theory (DFT) is used to evaluate changes to the electronic
structure of a platinum cluster interacting with a graphite substrate
and their effects on CO adsorption on the cluster. Results are correlated
with structural and electronic properties of platinum nanoparticles.
The stability of Pt/carbon catalysts under electrochemical potential
cycling is correlated with the properties of carbon substrates
Colloidal Polymers from Dipolar Assembly of Cobalt-Tipped CdSe@CdS Nanorods
The synthesis of a modular colloidal polymer system based on the dipolar assembly of CdSe@CdS nanorods functionalized with a single cobalt nanoparticle âtipâ (CoNP-tip) is reported. These heterostructured nanorods spontaneously self-assembled <i>via</i> magnetic dipolar associations of the cobalt domains. In these assemblies, CdSe@CdS nanorods were carried as densely grafted side chain groups along the dipolar NP chain to form bottlebrush-type colloidal polymers. Nanorod side chains strongly affected the conformation of individual colloidal polymer bottlebrush chains and the morphology of thin films. Dipolar CoNP-tipped nanorods were then used as âcolloidal monomersâ to form mesoscopic assemblies reminiscent of traditional copolymers possessing segmented and statistical compositions. Investigation of the phase behavior of colloidal polymer blends revealed the formation of mesoscopic phase separated morphologies from segmented colloidal copolymers. These studies demonstrated the ability to control colloidal polymer composition and morphology in a manner observed for classical polymer systems by synthetic control of heterostructured nanorod structure and harnessing interparticle dipolar associations
Directing the Deposition of Ferromagnetic Cobalt onto Pt-Tipped CdSe@CdS Nanorods: Synthetic and Mechanistic Insights
A methodology providing access to dumbbell-tipped, metalâsemiconductor and metal oxideâsemiconductor heterostructured nanorods has been developed. The synthesis and characterization of CdSe@CdS nanorods incorporating ferromagnetic cobalt nanoinclusions at both nanorod termini (<i>i</i>.<i>e</i>., dumbbell morphology) are presented. The key step in the synthesis of these heterostructured nanorods was the decoration of CdSe@CdS nanorods with platinum nanoparticle tips, which promoted the deposition of metallic CoNPs onto Pt-tipped CdSe@CdS nanorods. Cobalt nanoparticle tips were then selectively oxidized to afford CdSe@CdS nanorods with cobalt oxide domains at both termini. In the case of longer cobalt-tipped nanorods, heterostructured nanorods were observed to self-organize into complex dipolar assemblies, which formed as a consequence of magnetic associations of terminal CoNP tips. Colloidal polymerization of these cobalt-tipped nanorods afforded fused nanorod assemblies from the oxidation of cobalt nanoparticle tips at the ends of nanorods <i>via</i> the nanoscale Kirkendall effect. Wurtzite CdS nanorods survived both the deposition of metallic CoNP tips and conversion into cobalt oxide phases, as confirmed by both XRD and HRTEM analysis. A series of CdSe@CdS nanorods of four different lengths ranging from 40 to 174 nm and comparable diameters (6â7 nm) were prepared and modified with both cobalt and cobalt oxide tips. The total synthesis of these heterostructured nanorods required five steps from commercially available reagents. Key synthetic considerations are discussed, with particular emphasis on reporting isolated yields of all intermediates and products from scale up of intermediate precursors