Showing papers by "Malcolm L. H. Green published in 2002"
TL;DR: The combination of high surface area, robust immobilization and inherent nanotube electrochemical properties is of promising application in bioelectrochemistry.
Abstract: Metalloproteins and enzymes can be immobilized on SWNTs of different surface chemistry. The combination of high surface area, robust immobilization and inherent nanotube electrochemical properties is of promising application in bioelectrochemistry.
409 citations
TL;DR: In his famous 1959 address "There's Plenty of Room at the Bottom" as mentioned in this paper, Richard Feynman stated: "What could we do with layered structures with just the right layers? What would the properties of materials be if we could really arrange the atoms the way we want them? They would be very interesting to investigate theoretically. I can hardly doubt that when we have some control of the arrangement of things on a small scale, we will get an enormously greater range of possible properties that substances can have, and of different things that we can do.
185 citations
TL;DR: Carboxylate chemistry is used to covalently couple metal nanoparticles to defect sites in controllably oxidized single-walled carbon nanotube termini and side-walls, and this process monitored by atomic force microscopy as mentioned in this paper.
174 citations
TL;DR: In this article, the synthesis of high-surface-area molybdenum carbides has been studied by the temperature-programmed carburization of molybenum trioxide MoO3.
Abstract: The synthesis of high-surface-area molybdenum carbides has been studied by the temperature-programmed carburization of molybdenum trioxide MoO3. The feedstocks used were mixtures of methane and ethane with hydrogen. The solid reaction products were characterized at selected intervals using thermogravimetric analysis differential scanning calorimetry (TGA-DSC), surface area measurement (BET), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The gaseous products of the carburization process were monitored using a gas chromatograph equipped with a mass spectrometer (GC-MS). The structural properties of the product carbides are shown to depend on the conditions of synthesis. The C2H6/H2 feedstock gave the highest-surface-area material. The presence of H2 in the feed mixture reduced the amount of amorphous carbon deposited an the molybdenum carbide material. The surface area was found to increase most rapidly during the initial H2-reduction stage. Initially, the MoO3 is re...
158 citations
TL;DR: In this paper, the authors synthesize cobalt nanoparticles encapsulated in carbon shells by catalytic chemical vapor deposition (CCVD) in high yield by reducing with a H2/CH4 gas mixture a Mg0.9Co0.1O solid soluti...
Abstract: Cobalt nanoparticles encapsulated in carbon shells have been synthesized by catalytic chemical vapor deposition (CCVD) in high yield by reducing with a H2/CH4 gas mixture a Mg0.9Co0.1O solid soluti...
158 citations
TL;DR: A series of Na-W-Mn/SiO 2 catalysts with different sodium, tungsten, and manganese contents (wt.%) were prepared and their catalytic performance for the oxidative coupling of methane (OCM) was evaluated in a continuous micro-reactor as discussed by the authors.
Abstract: A series of Na-W-Mn/SiO 2 catalysts with different sodium, tungsten, and manganese contents (wt.%) were prepared and their catalytic performance for the oxidative coupling of methane (OCM) was evaluated in a continuous micro-reactor. The structural properties of the catalysts have been characterised using XPS, laser Raman spectroscopy (LRS), and X-ray diffraction (XRD). The results show that the catalysts containing Na, W, and Mn between the range of 0.4–2.3, 2.2–8.9, and 0.5–3.0 wt.%, respectively, had high CH 4 conversion and high selectivity to C 2 hydrocarbons in the OCM reaction. The addition of sodium to the catalyst is believed to bring about the migration of manganese to the catalyst surface, as both elements are found in high concentrations in this area. CH 4 conversion and the selectivity to C 2 H 4 are closely related to the surface Mn concentration of the catalysts. Both Na-O-Mn and Na-O-W act as the active centres of the catalysts for the oxidative coupling of methane. The catalyst surface is mainly covered with Na and O, while the Mn and W are present in the sub-surface of the catalyst. There is a synergic effect of sodium, tungsten, and manganese components, and the Na 2 W 2 O 7 crystalline phase is active for the oxidative coupling of methane.
145 citations
TL;DR: The structural chemistry of nanoscale materials encapsulated within single-walled carbon nanotubes (SWNTs) is reviewed, and their internal van der Waals surfaces regulate the growth behavior of encapsulated crystals in a precise fashion, leading to atomically regulated growth.
Abstract: The structural chemistry of nanoscale materials encapsulated within single-walled carbon nanotubes (SWNTs) is reviewed. SWNTs form atomically thin channels within a restricted diameter range, and their internal van der Waals surfaces regulate the growth behavior of encapsulated crystals in a precise fashion, leading to atomically regulated growth. The structural properties of these systems are largely dictated by the structural chemistry of the bulk material, although significant deviations from bulk structures are often observed, with lower surface coordinations and substantial lattice distortions.
95 citations
TL;DR: In this article, the Cationic and neutral methyl complexes of Pd(II) incorporating di-N-heterocyclic carbenes, tBuCCmeth and TBuCCeth (where tBuccmeth = 1,1′-methylene-3,3′-di-tert-butyldiimidazol-2,2′)-diylidene and TbuCCeth======
Abstract: Cationic and neutral methyl complexes of Pd(II) incorporating di-N-heterocyclic carbenes, tBuCCmeth and tBuCCeth (where tBuCCmeth
= 1,1′-methylene-3,3′-di-tert-butyldiimidazol-2,2′-diylidene and tBuCCeth
= 1,2-ethylene-3,3′-di-tert-butyldiimidazol-2,2′-diylidene), have been prepared. The complexes [Pd(tBuCCmeth)Me2] (1) and [Pd(tBuCCeth)Me2] (2) have been isolated and 2 has been characterised by single crystal X-ray diffraction. When 1 and 2 are dissolved in deuterated methanol in the presence of pyridine or bipyridine the four coordinate cations
[Pd(tBuCCmeth)Me(py)]+ (3), [Pd(tBuCCeth)Me(py)]+ (4), [Pd(tBuC(D)-η-Cmeth)Me(η2-bipy)]+ (5), and [Pd(tBuC(D)-η-Ceth)Me(η2-bipy)]+ (6), are observed spectroscopically.
84 citations
TL;DR: In this article, a series of molybdenum carbide catalysts were prepared using 10% C 2 H 2 /H 2 to carburize moly bdenum trioxide at different temperatures, and their performance was evaluated using methane partial oxidation to synthesis gas as the model reaction.
65 citations
TL;DR: High-resolution transmission electron microscopy and spatially resolved electron loss spectroscopy have revealed that a eutectic mixture of AgCl and AgI crystallizes within single walled carbon nanotubes (SWNTs) as metastable AgCl(1-)(x)I(x) 1D solid solution crystals.
Abstract: High-resolution transmission electron microscopy and spatially resolved electron loss spectroscopy have revealed that a eutectic mixture of AgCl and AgI crystallizes within single walled carbon nanotubes (SWNTs) as metastable AgCl(1-)(x)I(x) 1D solid solution crystals. The incorporated halide crystals form wurzite "tunnel" structures with locally varying Cl:I ratios and reduced Ag coordination.
63 citations
TL;DR: In this article, the performance of molybdenum carbide catalyst for partial oxidation of methane to syngas has been evaluated in a micro-reactor under various conditions.
Abstract: The performance of molybdenum carbide catalyst for partial oxidation of methane to syngas has been evaluated in a micro-reactor under various conditions. The molybdenum carbide catalyst is stable in methane partial oxidation to syngas at high reaction temperatures, high pressures and with a low space velocity of reactants. Pre-treatment has a significant effect on the catalyst activity and selectivity. The reaction mechanism over molybdenum carbide has been studied using 13C isotope exchange and in situ laser Raman. It is seen that the carbon in the lattice of the molybdenum carbide takes an active part in the reaction. The deactivation of molybdenum carbide catalyst results from the oxidation of the catalyst surface.
TL;DR: A series of nickel and tungsten bimetallic oxides have been prepared using the solid state reaction of nickel nitrate and Tungsten trioxide, which were carburised under temperature-programmed conditions with a mixture of 20% CH4/H2 and 10% C2H6/H 2 to prepare the corresponding carbides as mentioned in this paper.
TL;DR: Ortho-carborane molecules have been inserted into single walled carbon nanotubes (SWNTs) and imaged directly by high resolution transmission electron microscopy (HRTEM); both discrete molecules and 'zig-zag' 1D chains of o- carborane 'petit pois' were observed to pack into the tubule capillaries.
TL;DR: A detailed study of step-by-step carburisation of WO3 using 20% CH4/H2 and 10% C2H6/H 2 under various conditions is described in this article.
Abstract: A detailed study of step-by-step carburisation of WO3 using 20%CH4/H2 and 10%C2H6/H2 under various conditions is described. The catalyst materials have been characterised using thermogravimetric analysis and differential scanning calorimetry (TGA-DTC), temperature programmed reaction (TPR), surface area measurement using the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and elemental X-ray micro-analysis (EDX). The structures of the product carbides were found to be functions of the conditions of synthesis. The use of C2H6/H2 gave the highest surface area materials. During the early steps in the carburisation process at lower temperatures, disorder intergrowth occurs and non-stoichiometric crystallographic shear
tungsten oxide (i.e. WO3−x), and then WO2 are formed. Three steps are identified during the conversion of WO3 to WC using 10% C2H6/H2. First WO2 is formed by the reduction with hydrogen at temperatures of 670–720 K. This is carburised to WOxCy or β-W2C between 800–870 K. Finally, a second carburisation occurs at temperatures between 870–920 K to produce α-WC.
TL;DR: In this paper, the excitation energy transfer rates between the excited states of a Tb(III) complex containing the ligand 1-phenyl-3-methyl-4-(trimethylacetyl)pyrazol-4-one, are described.
Abstract: The excitation energy transfer rates between the excited states of a Tb(III) complex containing the ligand 1-phenyl-3-methyl-4-(trimethylacetyl)pyrazol-4-one, are described. Energy transfer rate constants are derived from time-gated and time-correlated single photon counting measurements. Comparison with the analogous Gd(III) complex shows that there is efficient intramolecular energy transfer from a singlet state of the ligand to excited terbium f-electron states. There is no evidence of bi-exciton annihilation in these materials, even at very high exciton densities. The use of this complex as the active medium for electroluminescent device applications is addressed. We note the particular properties of the ligand which make it suitable for this application and suggest possible improvements.
TL;DR: Cluster-derived bimetallic nanoparticles have been deposited onto multi-wall carbon nanotubes and shown to be generally homogeneously dispersed, of uniform small sizes, of the same composition as the starting mixed-metal clusters, and have a tendency to align at the tips of the tubules as mentioned in this paper.
TL;DR: In this article, Molybdenum carbide was used as a catalyst for the partial oxidation of methane to syngas in the presence of H2S, and the structure of the carbide catalyst was unchanged, but the rate of carbon deposition over the reactor wall and in the catalyst bed increased.
Abstract: Molybdenum carbide was tested as a catalyst for the partial oxidation of methane to syngas in the presence of H2S. The fresh and used catalysts have been characterized using XRD, laser Raman and SEM-TEM. It is suggested that H2S concentration higher than 0.1 wt% in the feedstock results in conversion of the carbide phase to sulfide, and also promotes the oxidation of the carbide catalyst surface; the combined effect is catalyst deactivation. At low H2S concentration in the feedstock (<0.1 wt%) the structure of the carbide catalyst was unchanged, but the rate of carbon deposition over the reactor wall and in the catalyst bed increased, again leading to the catalyst deactivation.
TL;DR: In this paper, a series of complexes in which the keto- or amidophosphine acts as a monodentate P ligand or as a neutral or anionic P,O chelating ligand have been synthesised and characterised.
Abstract: The reactions of the ligands Ph2PCH2C(O)R (R = Ph, NPh2) with the η6-arene molybdenum complexes [Mo(η3-C3H5)(μ-Cl)(η6-C6H5R)]2 (R = H, Me) have been investigated. A series of complexes in which the keto- or amidophosphine acts as a monodentate P ligand or as a neutral or anionic P,O chelating ligand have been synthesised and characterised. The crystal structures of the compounds [Mo(η3-C3H5)Cl(η6-C6H5Me){Ph2PCH2C(O)Ph}], [Mo(η3-C3H5){Ph2PCH2C(O)NPh2-κ2P,O}(η6-C6H5Me)][PF6] and [Mo{Ph2PCHC(O)Ph-κ2P,O}2(η6-C6H5R)]
(R = H, Me) have been determined. Interesting differences in the reactivity of the ketophosphine ligand versus the amidophosphine ligand were discovered and an unprecedented hydrogen–deuterium exchange of methylene and olefinic protons has been observed for the coordinated neutral or anionic ketophosphine ligands.
01 Jan 2002
TL;DR: The reactions of amide-derived ligands Ph2PN(R)C(O)CH3 (R = H, CH3) with molybdenum arene complexes as mentioned in this paper have been investigated.
Abstract: The reactions of the amide-derived ligands Ph2PN(R)C(O)CH3 (R = H, CH3) with the molybdenum arene complexes [Mo(η3-C3H5)(μ-Cl)(η6-C6H5R)]2 (R = H, CH3) have been investigated. A series of complexes in which the functional ligand displays η1-phosphine, η2-acetamidophosphine and η2-phosphinoiminolate coordination have been synthesised and characterised. The crystal structures of the cationic compounds [Mo(η3-C3H5)(η6-C6H6){Ph2PN(R)C(O)CH3-κ2P,O}][PF6] (R = H, CH3) have been determined. The first example of a structurally characterised phosphinoiminolate complex [Mo(η3-C3H5)(η6-C6H6){Ph2PNC(O)CH3-κ2P,O}]
is also reported.
TL;DR: In this paper, the photochemical behavior of unbridged (1−6) and bridged zirconocenes (7r, 7m), whose substituents differ in both electron-donor and steric properties, was investigated.
Abstract: This paper reports the photochemical behaviour of unbridged (1−6) and bridged zirconocenes (7r, 7m), whose substituents differ in both electron-donor and steric properties. The study of the electronic spectra and EPR spin-trapping experiments showed the photogeneration of ligand- and zirconium-centred radicals at wavelengths higher than 350 nm. This feature makes these complexes suitable as photoinitiators for radical polymerisation processes. tert-Butyl acrylate polymerisation has been studied in detail and the results are particularly encouraging as far as the reaction yields and the stereochemistry are concerned. In particular, the complexes 4−6, due to the tuneability of their structure and their stability in solution, look the most promising reagents.
01 Jan 2002
TL;DR: In this article, the authors focus on methods of opening, filling, and purifying multiple and single-walled carbon nanotubes (MWTs) in the bulk by a modified Kratschmer-Huffmann procedure, where MWTs are formed in the carbon distilled on the cathode as a soft deposit covered by a hard cylindrical outer layer.
Abstract: Publisher Summary This chapter focuses on methods of opening, filling, and purifying multiple and single-walled carbon nanotubes. The multiple-walled carbon nanotubes (MWTs) can be prepared in the bulk by a modified Kratschmer–Huffmann procedure. MWTs are prepared from 1-cm-diameter graphite rods under ∼0.17 atm of helium and from an arc generated by a dc voltage of 30 V and a current of ∼180 A. The MWTs are formed in the carbon distilled on the cathode as a soft deposit covered by a hard cylindrical outer layer. The MWTs can then be removed from the soft inner core of the deposit and the outer shell is discarded. The nature of the products in the distillate obtained by this method can be radically altered by the introduction of additives to the source carbon electrode. Single-walled carbon nanotubes (SWTs) can be synthesized by coevaporating composite carbon rods mixed with certain metals, as in a modified Kratschmer–Huffmann-type experiment, and by laser vaporization of metal-doped graphite targets. Most techniques of SWT purification involve a method of isolating the undesired extraneous materials followed by some process of selective filtration.
28 Feb 2002
TL;DR: In this article, the filling of single (SWNTs) and double walled carbon nanotubes by two different p-block halides, TlCl and PbI2, was investigated.
Abstract: The filling of carbon nanotubes (CNTs) with one-dimensional (1D) crystals can be seen as one form of doping of the nanotubes. This may contribute to a modification of their physical properties, especially when the confinement of the crystals leads to reduced coordination of their surface ions. We report here the filling of single (SWNTs) and double walled carbon nanotubes (DWNTs) by two different p-block halides, TlCl and PbI2. In the latter case, we paid special attention to the influence of the CNT diameter on the structure of the confined crystals and conclude that different structures can be found, depending on the available inner space within the nanotubes capillaries.
28 Feb 2002
TL;DR: In this article, it was shown that either 2×2 or 3×3 KI crystals can be formed in SWNTs according to their diameter, and the application of advanced HRTEM imaging techniques to these materials was also described.
Abstract: The encapsulation of halides and other materials within SWNTs makes possible the study of 1D crystal structures formed on the smallest scale possible. For example, we have shown that either 2×2 or 3×3 atomic layer thick KI crystals can be formed in SWNTs according to their diameter. Such crystals have reduced coordination (e.g. all the atoms in the 2×2 crystal are 4:4 coordinated) and exhibit lattice distortions compared to the corresponding bulk halide. With respect to more complex binary structures, such as 3D network, chain halides, layered halides, or complex 3D oxides, 1D crystals of these structures can be studied. The application of advanced HRTEM imaging techniques to these materials is also described.
TL;DR: In this article, the chiral sense of a single-walled carbon nanotube (SWNT) was identified from a phase image that was recovered via a modified object wave restoration scheme.
Abstract: The detailed inclusion crystallography of a one-dimensional valentinite Sb2O3 crystal incorporated within a helical (21, −8) single-walled carbon nanotube (SWNT) was identified from a phase image that was recovered via a modified object wave restoration scheme. A detailed analysis of asymmetric fringe contrast in the tube walls provided strong evidence for the chiral sense of the tube itself. Due to the good agreement of the observed wall periodicity with the determined absolute focus values and power spectra obtained from single-pixel line traces along both tube walls, we were able to determine the chiral sense of the SWNT and the tilt angle of the Sb2O3/SWNT composite relative to the electron beam. The angle between the optimum
$$\left\langle {10\bar 1} \right\rangle $$
viewing direction of the crystal fraction and the tube axis, which is aligned with the
$$\left\langle {4\bar 12} \right\rangle $$
direction of the Sb2O3 crystal, is 78.3°. Since small deviations from this viewing direction make an insignificant difference to the observed contrast, a tube inclination of 15° is plausible for both the Sb2O3 crystal and the assigned (21, −8) SWNT, which is the mirror image of a (13, 8) SWNT.
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: Spatially resolved electron loss spectra (EELS) have been recorded for single walled carbon nanotubes (SWNTs) filled with metastable crystalline AgCl1−xIx as discussed by the authors.
Abstract: Spatially resolved electron loss spectra (EELS) have been recorded for single walled carbon nanotubes (SWNTs) filled with metastable crystalline AgCl1−xIx. High resolution transmission electron microscopy (HRTEM) revealed that the incorporated halide crystals are derived from a 1D wurzite ‘tunnel’ structure with reduced Ag coordination with Cl and I randomly distributed over the halogen sites. High resolution EELS line scan profiles were used to probe the local composition of the nanocomposites and to distinguish between filled and unfilled tubules.
02 Oct 2002-Structural and Electronic Properties of Molecular Nanostructures. XVI International Winterschool on Electronic Properties of Novel Materials
TL;DR: Nanotubes are non‐destructively oxidized along their sidewalls and covalently functionalized with metal nanoparticles via carboxylate chemistry, and individual nanotube reaction products are characterized by atomic force microscopy.
Abstract: Nanotubes are non‐destructively oxidized along their sidewalls and covalently functionalized with metal nanoparticles via carboxylate chemistry. Proteins adsorb individually, strongly and non‐covalently along nanotube lengths. Individual nanotube reaction products are characterized by atomic force microscopy.