Rotationally Restricted 1,1′-Bis­(phenylethynyl)ferrocene Subunits in Macrocycles

The synthesis of macrocycles comprising a 1,1′-bis(phenylethynyl)ferrocene subunit was developed to increase the structural control over the spatial arrangement of the two cyclopentadienyl ligands of the ferrocene junction. The target structures were obtained through a modular strategy that enables the assembly of varying ring sizes from a common precursor. In particular, macrocycles were either formed by an ether formation reaction or by ring-closing metathesis reactions. The macrocycles were obtained in reasonable isolated yields, which allowed their thorough characterization by one- and two-dimensional NMR spectroscopy experiments, and the identity of one macrocycle was corroborated by single-crystal X-ray diffraction

Carbon Nanotube Materials for Substrate Enhanced Control of Catalytic Activity

Carbon SWNTs are attractive materials for supporting electrocatalysts. The properties of SWNTs are highly tunable and controlled by the nanotube's circumferential periodicity and their surface chemistry. These unique characteristics suggest that architectures constructed from these types of carbon support materials would exhibit interesting and useful properties. Here, we expect that the structure of the carbon nanotube support will play a major role in stabilizing metal electrocatalysts under extreme operating conditions and suppress both catalyst and support degradation. Furthermore, the chemical modification of the carbon nanotube surfaces can be expected to alter the interface between the catalyst and support, thus, enhancing the activity and utilization of the electrocatalysts. We plan to incorporate discrete reaction sites into the carbon nanotube lattice to create intimate electrical contacts with the catalyst particles to increase the metal catalyst activity and utilization. The work involves materials synthesis, design of electrode architectures on the nanoscale, control of the electronic, ionic, and mass fluxes, and use of advanced optical spectroscopy techniques

Encapsulation of cadmium selenide nanocrystals in biocompatible nanotubes: DFT calculations, X-ray diffraction investigations and confocal fluorescence imaging

The encapsulation of CdSe nanocrystals within singlewalled carbon nanotubes (SWNTs) cavities of varying dimensions at elevated temperatures under strictly air-tight conditions is described for the first time. The structures of CdSe nanocrystals under confinement inside SWNTs was established in a comprehensive study, combining both experimental and DFT level theoretical investigations. The calculated binding energies show that all considered polymorphs (3, 3), (4, 4) and (4,2) may be obtained experimentally. The most thermodynamically stable structure (3:3) is directly compared to the experimentally observed CdSe structures inside carbon nanotubes. The gas-phase density functional theorycalculated energy differences between “free” 3:3 and 4:2 structures (e.g. whereby 3:3 models a novel tubular structure in which both Cd and Se form three coordination as observed experimentally for HgTe inside SWNT and 4:2 is a motif derived from the hexagonal CuI bulk structure in which both Cd and Se form 4 or 2 coordinations) are surprisingly small, only 0.06 eV per formula unit.. X-ray powder diffraction, Raman spectroscopy, High-resolution transmission electron microscopy (HRTEM) and Energy Dispersive X-ray (EDX) analyses led to the full characterization of the SWNTs filled with the CdSe nanocrystals, shedding light on the composition, structure and the electronic interactions of the new nanohybrid materials on an atomic level. A new emerging hybrid nanomaterial, simultaneously filled and beta-D-glucan coated was obtained using pristine nanotubes and bulk CdSe powder as starting materials. This displayed fluorescence in water dispersions and unexpected biocompatibility was found to be mediated by the beta-D-glucan (a biopolymer extracted from barley) with respect to that of the individual inorganic materials components. For the first time, such supramolecular nanostructures are investigated by life-sciences techniques applied to functional nanomaterials characterization opening the doors for future nano-biotechnological applications

Self-Assembly of Linear Arrays of Semiconductor Nanoparticles on Carbon Single-Walled Nanotubes †

Ligand-stabilized nanocrystals (NCs) were strongly bound to the nanotube surfaces by simple van der Waals forces. Linear arrays of CdSe and InP quantum dots were formed by self-assembly using the grooves in bundles of carbon single-walled nanotubes (SWNTs) as a one-dimensional template. A simple geometrical model explains the ordering in terms of the anisotropic properties of the nanotube surface. CdSe quantum rods were also observed to self-organize onto SWNTs with their long axis parallel to the nanotube axis. This approach offers a route to the formation of ordered NC/SWNT architectures that avoids problems associated with surface derivatization. Both semiconductor quantum dots (QDs) 1 and carbon singlewalled nanotubes (SWNTs) 2 possess interesting and potentially useful optical and electronic properties due to their nanoscale structures. In the case of QDs, quantum confinement in three dimensions produces a size-dependent modification of the electronic band structure, resulting in the formation of discrete electronic states. QDs exhibit unique behaviors such as efficient photoluminescence and photon up-conversion, slowed relaxation and cooling of hot carriers, enhanced lasing, and carrier multiplication via impact ionization. 3 SWNTs, however, consist of sp 2 -hybridized carbon atoms that form the walls of nanometer-wide, seamless cylinders. Past efforts to attach semiconductor nanocrystals (NCs) to nanotubes have focused on forming chemical attachments between the two different nanostructures. In this approach, defects in the nanotube lattice, i.e., any site where the sp 2 -bonded carbon network is broken, are used as sites for chemical bond formation. Such defects are typically present after acid-based purification methods or may be specifically introduced by chemical derivatization. In this paper, we report the formation of organized, onedimensional (1-D) arrays of semiconductor QDs by van der Waals (vdW) adsorption onto SWNTs. Two representative II-VI and the III-V semiconductor NCs, CdSe and InP, respectively, demonstrated linear ordering when adsorbed from nonaqueous colloidal solutions onto high-purity, low-defectdensity SWNTs. The tendency to form linear arrays was greatest when tube-tube alignment was relatively good within bundles and when the QDs were relatively large. The edge-to-edge (ee) separation distance between QDs in the 1-D arrays was ∼18 Å for both the InP and the CdSe QDs, indicating that QD-QD separation is governed by the thickness of the ligand shells, as is the case in two-and three-dimensional QD arrays

DOE Carbon-based Hydrogen Storage Center of Excellence: Center Highlights and NREL Activities

Presented at the 2006 DOE Hydrogen, Fuel Cells & Infrastructure Technologies Program Annual Merit Review in Washington, D.C., May 16-19, 2006

Controlled Growth of Carbon Nanotubes on Conductive Metal Substrates for Energy Storage Applications

The impressive mechanical and electronic properties of carbon nanotubes (CNTs) make them ideally suited for use in a variety of nanostructured devices, especially in the realm of energy production and storage. In particular, vertically-aligned CNT “forests” have been the focus of increasing investigation for use in supercapacitor electrodes and as hydrogen adsorption substrates. Vertically-aligned CNT growth was attempted on metal substrates by waterassisted chemical vapor deposition (CVD). CNT growth was catalyzed by iron-molybdenum (FeMo) nanoparticle catalysts synthesized by a colloidal method, which were then spin-coated onto Inconel® foils. The substrates were loaded into a custom-built CVD apparatus, where CNT growth was initiated by heating the substrates to 750 °C under the fl ow of He, H2, C2H4 and a controlled amount of water vapor. The resultant CNTs were characterized by a variety of methods including Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM), and the growth parameters were varied in an attempt to optimize the purity and growth yield of the CNTs. The surface area and hydrogen adsorption characteristics of the CNTs were quantifi ed by the Brunauer- Emmett-Teller (BET) and Sieverts methods, and their capacitance was measured via cyclic voltammetry. While vertically-aligned CNT growth could not be verifi ed, TEM and SEM analysis indicated that CNT growth was still obtained, resulting in multiwalled CNTs of a wide range in diameter along with some amorphous carbon impurities. These microscopy fi ndings were reinforced by Raman spectroscopy, which resulted in a G/D ratio ranging from 1.5 to 3 across different samples, suggestive of multiwalled CNTs. Changes in gas fl ow rates and water concentration during CNT growth were not found to have a discernable effect on the purity of the CNTs. The specifi c capacitance of a CNT/FeMo/Inconel® electrode was found to be 3.2 F/g, and the BET surface area of a characteristic CNT sample was measured to be 232 m2/g with a cryogenic (77K) hydrogen storage of 0.85 wt%. This level of hydrogen adsorption is slightly higher than that predicted by the Chahine rule, indicating that these CNTs may bind hydrogen more strongly than other carbonaceous materials. More work is needed to confi rm and determine the reason for increased hydrogen adsorption in these CNTs, and to test them for use as catalyst support networks. This study demonstrates the feasibility of producing CNTs for energy storage applications using water-assisted CVD