Effect of particle size on iron nanoparticle oxidation state

Selecting catalyst particles is a very important part of carbon nanotube growth, although the properties of these nanoscale particles are unclear. In this article iron nanoparticles are analyzed through the use of atomic force microscopy and x-ray photoelectron spectroscopy in order to understand how the size affects the chemical composition of nanoparticles and thus their physical structure. Initially, atomic force microscopy was used to confirm the presence of iron particles, and to determine the average size of the particles. Next an analytical model was developed to estimate particle size as a function of deposition time using inputs from atomic force microscopy measurement. X-ray photoelectron spectroscopy analysis was then performed with a focus on the spectra relating to the 2p Fe electrons to study the chemical state of the particles as a function of time. It was shown that as the size of nanoparticles decreased, the oxidation state of the particles changed due to a high proportion of atoms on the surface.     

Synthesis and Characterization of Niobium-doped TiO2 Nanotube Arrays by Anodization of Ti-20Nb Alloys

Well crystallized niobium-doped TiO₂ nanotube arrays（TiNbO-NT） were successfully synthesized via the anodization of titanium/niobium alloy sheets,followed with a heat treatment at 550 C for 2 h.Morphology analysis results demonstrated that both the titanium/niobium alloy microstructure and the dissolution strength of electrolyte played major roles in the formation of nanotube structure.A single-phase microstructure was more favorable to the formation of uniform nanotube arrays,while modulating the dissolution strength of electrolyte was required to obtain nanotube arrays from the alloys with multi-phase microstructures.X-ray diffraction（XRD） and X-ray photoelectron（XPS） analysis results clearly demonstrated that niobium dopants（Nb 5+） were successfully doped into TiO₂ anatase lattice by substituting Ti 4+ in this approach.     

Thermodynamic approach to enhanced dispersion and physical properties in a carbon nanotube/polypeptide nanocomposite

A high molecular weight synthetic polypeptide has been designed which exhibits favorable interactions with single wall carbon nanotubes (SWCNTs). The enthalpic and entropic penalties of mixing between these two molecules are reduced due to the polypeptide's aromatic sidechains and helical secondary structure, respectively. These enhanced interactions result in a well dispersed SWCNT/Poly (l-Leucine-ran-l-Phenylalanine) nanocomposite with enhanced mechanical and electrical properties using only shear mixing and sonication. At 0.5 wt% loading of SWCNT filler, the nanocomposite exhibits simultaneous increases in the Young's modulus, failure strain, and toughness of 8%, 120%, and 144%, respectively. At 1 kHz, the same nanotube loading level also enhances the dielectric constant from 2.95 to 22.81, while increasing the conductivity by four orders of magnitude.     

The rectifying effect of heterojunctions composed of carbon and boron nitride nanotubes

We investigate the electronic transport properties of several nanotube heterojunctions which are composed of carbon and boron nitride nanotubes (i.e., CNTs and BNNTs), using the non-equilibrium Green's function method combined with the density functional theory. The results reveal that, the pristine (n, n) and (n, 0) CNTs are metal and present the linear I–V curves, and the BNNTs are semiconductors and little current can be propagated through. While when the (n, n)CNT and (n, n)BNNT are combined into a heterojunction, it displays a perfect rectifying effect. When different types of CNTs (i.e., (n, 0) and (n, n) CNTs) are combined into a heterojunction, its I–V curve still presents a linear behavior. Interestingly, however, if the outside surface of the (n, n) CNT is fluorinated to tune its electronic structures, it will display a perfect rectifying effect. These proposed nanotube heterojunctions have a significant potential value in the field of nano rectifiers.     

Solid state nuclear magnetic resonance studies of nanocarbons

In the present article we review Nuclear Magnetic Resonance studies of different kinds of nanocarbons, such as nanodiamonds, nanographites, pure and doped fullerenes, giant carbon fullerenes and carbon nanotubes.     

The Role of Fullerene-Like Structures in Carbon Black and Their Interaction with Dienic Rubber

Abstract

The identification of fullerene-like sites on carbon black surface and in particular the pentagonal or corannulene-type sites, has permitted us to explain the chemical interaction between filler and polymer (diene rubber) occurring during mixing in terms of free radical and Diels-Alder addition of polymer chains on the fullerene-like sites of carbon black. The free radicals and diene sites are formed on rubber chains during mixing by the mechanochemical degradation, which is caused by shear stresses.

We have also noticed the curious analogy between the turbostratic morphology of carbon black particles and the onion-like graphitic particles.     

Effect of packing on the cluster nature of C nanotubes: An information entropy analysis

The possibility of the existence of single−wall carbon nanotubes (SWNTs) in organic solvents in the form of clusters is discussed. A theory is developed based on a bundlet model for clusters, which enables describing the distribution function of clusters by size. Comparison of the calculated values of solubility with experiments would permit obtaining energetic parameters characterizing the interaction of an SWNT with its surrounding, in a solid or solution. Fullerenes and SWNTs are unique objects, whose behaviour in many physical situations is characterized by remarkable peculiarities. Peculiarities in solutions show up first in that fullerenes and SWNTs represent the only soluble forms of carbon, what is related to the originality in the molecular structure of fullerenes and SWNTs. The fullerene molecule is a virtually uniform closed spherical or spheroidal surface, and an SWNT is a smooth cylindrical unit. Both structures give rise to the relatively weak interaction between the neighbouring molecules in a crystal and promote interaction of the molecules with those of a solvent. Another peculiarity in solutions is related to their trend to form clusters, consisting of a number of fullerene molecules or SWNTs. The energy of interaction of a fullerene molecule or SWNT with solvent molecules is proportional to the surface of the former molecule and roughly independent of the orientation of solvent molecules. All these phenomena have a unified explanation in the framework of the bundlet model of a cluster, in accordance with which the free energy of an SWNT involved in a cluster is combined from two components, viz. a volume one proportional to the number of molecules n in a cluster, and a surface one proportional to n^1/2. Algorithms for classification are proposed based on the criteria information entropy and its production. Many classification algorithms are based on information entropy. When applying these procedures to sets of moderate size, an excessive number of results appear compatible with data, and this number suffers a combinatorial explosion. However, after the equipartition conjecture, one has a selection criterion between different variants resulting from classification between hierarchical trees. According to this conjecture, for a given charge or duty, the best configuration of a flowsheet is the one in which the entropy production is most uniformly distributed. Information entropy, cluster and principal component analyses agree.     

Mineralization of flagella for nanotube formation

Flagella isolated from Salmonella typhimurium were used as a template for the formation of TiO₂ nanotubes, which was accomplished through recent advances in low temperature ceramic film processing. TiO₂ is precipitated onto or attracted to the flagellar surface in aqueous solution. The mechanism of mineral film formation is similar to that of biominerals in nacre, sea urchin spine, and sponge spicule. This process is advantageous over other mineralization processes, as no genetic modification of the flagella is necessary and the mineralization is done at low temperature in aqueous solution.     

Electrochemical synthesis of self-organized TiO2 nanotubular structures using an ionic liquid (BMIM-BF4)

We show that an ionic liquid consisting of imidazolium salt with a BF₄ counter ion (BMIM-BF₄) can directly be used to grow well-defined layers of self-organized TiO₂ nanotubes. For this a Ti metal substrate is anodized in this electrolyte for potential range between 3 V_Ag/AgCl and 10 V_Ag/AgCl without addition of free fluoride species (fluorides are used in all previous tube growth procedures). Key factors that influence the morphology and geometry of the resulting nanotubular layer are the anodic potential, the anodization time and particularly the water content in the ionic liquid. The resulting nanotubes layers have thickness in the range of approximately 300-650 nm; with individual tubes that have diameters between 27 nm and 43 nm.     

Cobalt supported on carbon nanotubes — A promising novel Fischer–Tropsch synthesis catalyst

An extensive study of Fischer–Tropsch synthesis (FTS) on carbon nanotubes (CNT) supported and γ–alumina-supported cobalt catalysts with different amounts of cobalt are reported. Up to 40 wt.% of cobalt is added to the supports by the impregnation method. The effect of the support on the reducibility of the cobalt oxide species, dispersion of the cobalt, average cobalt clusters size, water–gas shift (WGS) activity and activity and selectivity of FTS is investigated. Using carbon nanotubes as cobalt catalyst support was found to cause the reduction temperature of cobalt oxide species to shift to lower temperatures. The strong metal-support interactions are reduced to a large extent and the reducibility of the catalysts improved significantly. CNT aided in well dispersion of metal clusters and average cobalt clusters size decreased. Results are presented showing that the hydrocarbon yield obtained by inventive CNT supported cobalt catalyst is surprisingly much larger than that obtained from cobalt on alumina supports. The maximum concentration of active surface Co° sites and FTS activity for alumina and CNT supported catalysts are achieved at 34 wt.% and 40 wt.% cobalt loading respectively. CNT caused a slight decrease in the FTS product distribution to lower molecular weight hydrocarbons.