Jeremy Sloan

Graphene Oxide: Structural Analysis and Application as a Highly Transparent Support for Electron Microscopy

We report on the structural analysis of graphene oxide (GO) by transmission electron microscopy (TEM). Electron diffraction shows that on average the underlying carbon lattice maintains the order and lattice-spacings of graphene; a structure that is clearly resolved in 80 kV aberration-corrected atomic resolution TEM images. These results also reveal that single GO sheets are highly electron transparent and stable in the electron beam, and hence ideal support films for the study of nanoparticles and macromolecules by TEM. We demonstrate this through the structural analysis of physiological ferritin, an iron-storage protein.

The immobilisation of proteins in carbon nanotubes

Carbon nanotubes, fullerene-related structures, have been used for the immobilisation of proteins and enzymes. We have been able to demonstrate, for the first time, direct imaging by high resolution transmission electron microscopy of Zn2Cd5-metallothionein, cytochromes c, c, and β-lactamase 1. This was achieved, without modification, because the biomolecules encapsulated within nanotubes appear to be shielded from the consequences of exposure to the intense electron beam. The results indicate that the internal surface of the nanotubes interacts strongly with the enzymes resulting in their immobilisation. In some cases, the proteines are seen to be distorted giving a concave meniscus inside the tubes. Single protein molecules, their dimers, tetramers and higher oligomers are observed inside the central cavity. Comparison of the catalytic activities of immobilised β-lactamase 1 on or in nanotubes with the free enzyme in the hydrolysis of penicillin, however, showed a significant amount of the immobilised enzyme remained catalytically active, implying that no drastic conformational change had taken place. The carbon nanotube appears to act as a benign host in its ability to encapsulate protein molecules within an environment which offers some protection.

Double-walled carbon nanotubes fabricated by a hydrogen arc discharge method

Abstract Double walled carbon nanotubes (DWNTs) were obtained by the arc discharge technique in an atmosphere of Ar and H 2 mixture (1:1/v:v) at 350 Torr. The catalyst was prepared from a mixture of Ni, Co, Fe and S powders heated in an inert gas atmosphere at 500°C for 1 h. High resolution electron microscopy (HREM) revealed that the dominant type of obtained nanotubes were DWNTs with outer diameter in the range of 1.9–5 nm and inner tube diameters in the range 1.1–4.2 nm. As a rule, the DWNT tubes form into bundles. Occasionally single walled nanotubes (SWNTs) were observed by HREM although Raman spectroscopy did not reveal the presence of significant quantities of these tubules in the bulk product.

Inorganic fullerene-like material as additives to lubricants: structure–function relationship

Abstract Recently, inorganic fullerene-like (IF) supramolecules of metal dichalcogenide MX2 (M=Mo, W, etc.; X=S, Se), materials with structures closely related to (nested) carbon fullerenes and nanotubes have been synthesized. The main goal of the present work was to study the tribological properties of IF–WS2 in comparison to 2H–WS2 and MoS2 platelets over a wide range of loads and sliding velocities. The size and shape distributions of the nanoparticles were studied by transmission electron microscopy (TEM). The average size of the IF–WS2 particles was 120 nm, while that of 2H–WS2 and 2H–MoS2 was 0.5 μm and 4 μm. The chemical reactivity of the different powders in an oxygenated atmosphere was verified by heating the powders in ambient atmosphere. The friction experiments were performed in laboratory atmosphere (humidity ∼50%) using a ring-block tester. Complementary information on the state of wear of the powders in the lubricating fluid and on the metal surfaces of the specimens was obtained using a combination of TEM, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). It has been established that IF–WS2 nanoparticles appear to have excellent tribological properties in definite loading range in comparison to typical metal dichalcogenides. The oxidation of the IF particles and the wear track was essentially less than with solid lubricants made of platelets of the same chemical compound (WS2). The main advantages of IF nanoparticles lie in their round shape and the absence of dangling bonds.

The size distribution, imaging and obstructing properties of C60 and higher fullerenes formed within arc-grown single walled carbon nanotubes

Abstract The relative size distributions of molecules of C60 and higher fullerenes observed in single walled carbon nanotubes (SWNTs) produced by arc vaporization of carbon in the presence of a mixed Ni/Y catalyst are described. The experimental and calculated imaging properties of the fullerenes, which were observed in ca. 5–10% of SWNTs, are also described. The in situ e-beam irradiation in a 300 kV field emission gun transmission electron microscope causes rapid coalescence of the fullerenes within the SWNTs. The incorporated fullerenes also directly impede crystal growth in SWNTs when their cavities are filled by the liquid phase capillary method.

Carbon nanotubes from polyethylene precursors: Structure and structural changes caused by thermal and chemical treatment revealed by HREM

High resolution electron microscopy (HREM) reveals that carbon nanotubes obtained by heating a polyethylene precursor in the presence of catalytic Ni particles have a structure consisting of stacked conical carbon layers. Two main types of nanotube structures were identified. When the conical angle along the tubes is in the range 16–35 °, “bamboo”-shaped nanotubes are observed, characterized by open carbon edges (OEs) that were assumed to terminate in hydrogen. When the conical angle is in the range 75–85 °, a “fish-bone”-type structure is observed. Following heat treatment in the temperature range 1200–2800 °C, the catalytic Ni particles were removed and the hydrogen content reduced. As a result, the neighboring OEs were linked together, revealed in the HREM by the formation of loops along both the external tube sides and also the insides of the inner channels. Chemically, the pre-heat treated tubes could withstand bromination, but were completely destroyed by treatment with hot concentrated HNO3. Treatment of the pre-heat treated tubes with molten V2O5 revealed no penetration of this material between the OEs along the external wall or into the inner channel. The microstructure of the catalytic Ni particles, present at the tips of the pre-heat treated nanotubes, was also investigated. Outer polycrystalline layers consisting of Ni3C and probably NiO were observed near the periphery of terminal Ni particles not covered with graphitic layers and also near that of open regions of partially covered particles.

Two layer 4:4 co-ordinated KI crystals grown within single walled carbon nanotubes

The formation of ‘all surface’ 4:4 co-ordinated KI crystals within 1.4 nm diameter single walled carbon nanotubes (SWNT) is reported. KI was inserted into the SWNTs by a capillary method [J. Sloan, D.M. Wright, H.G. Woo, S. Bailey, G. Brown, A.P.E. York, K.S. Coleman, J.L. Hutchison, M.L.H. Green, J. Chem. Soc. Chem. Commun. (1999) 699], whereby the nanotubes were combined intimately with the molten halide. The crystals grew withh 001 i (relative to bulk KI) parallel to the tubule axes and were continuous tetragonally distorted bilayer crystals composed of alternating columns of K‐I and I‐K pairs when viewed along h 100 i. ” 2000 Elsevier Science B.V. All rights reserved.

Capillarity and silver nanowire formation observed in single walled carbon nanotubes

Single walled carbon nanotubes (SWNTs) exhibit similar capillarity properties to those exhibited by multiple walled carbon nanotubes (MWNTs); SWNTs, previously filled in low yield (ca. 2%) by solution chemistry techniques, can be filled in high yield (up to ca. 50%) by the liquid phase method; compositions from the KCl–UCl4 and AgCl–AgBr systems were used to fill SWNTs without causing them significant chemical or thermal damage; in the case of the latter, exposure to light or an electron beam resulted in the partial photolytic reduction of SWNT incorporated silver halides to continuous metallic silver ‘nanowires’ within the capillaries.

Synthesis of carbon nanotubes containing metal oxides and metals of the d-block and f-block transition metals and related studies

The filling of carbon nanotubes with metals and metal oxidesvia one- and two-step processes is presented. Both molten media and wet chemistry solution methods have been used to introduce foreign materials into the hollow nanotube cavities. Chemical reactions inside the tubes have been carried out, including the reduction of encapsulated materials to the metals. The nature of the crystalline filling has been found to be highly dependent on the techniques used. Wet chemical methods tend to result in filling which consists of discrete crystallites, whereas molten media methods tend to give long, continuous single crystals.

Structural reorganization of cylindrical nanoparticles triggered by polylactide stereocomplexation

Co-crystallization of polymers with different configurations/tacticities provides access to materials with enhanced performance. The stereocomplexation of isotactic poly(L-lactide) and poly(D-lactide) has led to improved properties compared with each homochiral material. Herein, we report the preparation of stereocomplex micelles from a mixture of poly(L-lactide)-b-poly(acrylic acid) and poly(D-lactide)-b-poly(acrylic acid) diblock copolymers in water via crystallization-driven self-assembly. During the formation of these stereocomplex micelles, an unexpected morphological transition results in the formation of dense crystalline spherical micelles rather than cylinders. Furthermore, mixture of cylinders with opposite homochirality in either THF/H2O mixtures or in pure water at 65 °C leads to disassembly into stereocomplexed spherical micelles. Similarly, a transition is also observed in a related PEO-b-PLLA/PEO-b-PDLA system, demonstrating wider applicability. This new mechanism for morphological reorganization, through competitive crystallization and stereocomplexation and without the requirement for an external stimulus, allows for new opportunities in controlled release and delivery applications.