Mössbauer Study of Iron-Containing Carbon Nanotubes

⁵⁷Fe transmission Mössbauer at temperatures between 18 and 298 K and magnetic measurements have been used to characterize Fe-filled carbon nanotubes which were prepared by pyrolisis of Ferrocene + C₆₀ at atmospheric pressure under an Ar atmosphere at 1050°C. The Mössbauer data have shown that the Fe phases encapsulated within the carbon nanotubes are -Fe, Fe₃C and -Fe. The magnetic results are compatible with the Mössbauer data. Taken together the results allow us to propose a simple picture of the distribution of iron phases within the carbon nanotubes which would consist of an -Fe core surrounded by an -Fe shell, finally covered by an Fe₃C layer.     

Controllable and Predictable Viscoelastic Behavior of 3D Boron‐Doped Multiwalled Carbon Nanotube Sponges

3D carbon nanotube (CNT)‐based macrostructures are the subject of extensive attention because the outstanding properties of 1D and 2D nanostructures have not been fully translated into key engineering applications. Generation of 3D CNT architectures with covalent junctions could endow the new materials with extraordinary mechanical properties. In this study, detailed experimental characterization and statistical comparison are carried out on 3D boron‐doped multiwalled CNT (CB_xMWNT) sponges with covalent junctions and undoped multiwalled CNT (undoped‐MWNT) sponges without junctions. By investigating the plastic, elastic, viscoelastic, and dynamic viscoelastic properties of both sponges, as well as the dependency of these mechanical properties on material morphology, the CB_xMWNT sponge is found to be a more predictable and stable material than the undoped‐MWNT sponge. Statistical comparison proves that the excellent properties of the CB_xMWNT are attributed to its “elbow‐like” junctions inside the 3D networks, which prevent permanent buckling and bundling of the CNTs under extreme loading. Thus, by optimizing the covalent junctions in 3D CNT sponges, their functional behavior can be controlled and regulated. These findings may promote applications of 3D CNT sponges in various fields, including biomedical or high‐precision devices in which lightweight, controllable, and reliable mechanical properties are always desirable.     

Pyrolytic synthesis of long strands of large diameter single-walled carbon nanotubes at atmospheric pressure in the absence of sulphur and hydrogen

We describe the synthesis of cm-long strands consisting of single-walled carbon nanotube ropes. The method involves the thermolysis of ferrocene (FeCp₂)–alcohol solutions under an Ar atmosphere at 800–950 °C. The tubes within strands could exhibit large diameters (2–3.5 nm OD) in high yields by either increasing the ferrocene concentration in the alcohol solution or by increasing the pyrolysis temperature. We noted that the nanotube material with the highest degree of crystallinity was produced at 950 °C, and as the ferrocene concentration in the alcohol solution increases (e.g., 1.2 wt%), the tubes tend to be metallic. This method appears to be simple, safer and more efficient than others reported in the literature because it does not require vacuum, sulphur agents, relatively high temperatures or large amounts of H₂.     

The possible way to evaluate the purity of double-walled carbon nanotubes over single wall carbon nanotubes by chemical doping

Here, we carried out Raman study on chemically doped single wall carbon nanotube (SWNT)/double-walled carbon nanotube (DWNT) mixed bucky-papers. Their highly different Raman responses (e.g., a large upshift of tangential mode of SWNT and no large changes in the frequencies of tangential mode assigned to the outer tubes of the DWNT) upon doping with the sulfuric acid could be used as a qualitative indicator of the purity of the DWNT samples with the concentration of its SWNTs contents.     

Negatively curved graphite and triply periodic minimal surfaces

The Weierstrass representation has been used to construct negatively curved graphite in which atoms rest no a perfect triply periodic minimal surface. By applying the Bonnet transformation on a patch of the D surface decorated with graphite we have been able to construct the Gyroid and P minimal surfaces. Curvatures, densities and lattice parameters have been calculated. It has been found that the maximum Gaussian curvature for our negatively curved structures is less in magnitude than the Gaussian curvature ofC ₆₀. In addition, a new periodic graphitic set with the same topology as the I-WP minimal surface has been obtained by introducing pentagonal and octagonal rings.     

Hydrogen storage in nanoporous carbon materials: myth and facts

We used Grand canonical Monte Carlo simulation to model the hydrogen storage in the primitive, gyroid, diamond, and quasi-periodic icosahedral nanoporous carbon materials and in carbon nanotubes. We found that none of the investigated nanoporous carbon materials satisfy the US Department of Energy goal of volumetric density and mass storage for automotive application (6 wt% and 45 kg H(2) m(-3)) at considered storage condition. Our calculations indicate that quasi-periodic icosahedral nanoporous carbon material can reach the 6 wt% at 3.8 MPa and 77 K, but the volumetric density does not exceed 24 kg H(2) m(-3). The bundle of single-walled carbon nanotubes can store only up to 4.5 wt%, but with high volumetric density of 42 kg H(2) m(-3). All investigated nanoporous carbon materials are not effective against compression above 20 MPa at 77 K because the adsorbed density approaches the density of the bulk fluid. It follows from this work that geometry of carbon surfaces can enhance the storage capacity only to a limited extent. Only a combination of the most effective structure with appropriate additives (metals) can provide an efficient storage medium for hydrogen in the quest for a source of "clean" energy.     

Efficient anchorage of Pt clusters on N-doped carbon nanotubes and their catalytic activity

We report an efficient method for anchoring Pt clusters (e.g., 6 nm in size) on the surfaces of N-doped multi-walled carbon nanotubes (MWNTs-CN_x) using a relatively simple method consisting of a hydrothermal treatment of Na₂[PtCl₆] · 6H₂O and N-doped nanotubes dispersed in acetic acid. The catalytic properties of this material were evaluated finding that the conversion of cinnamaldehyde using Pt-coated MWNTs-CN_x could increase up to 6 times with respect to that obtained for uncoated MWNTs-CN_x and pure carbon CNTs. Therefore, we envisage this material could be either used as an efficient catalyst or as a sensor.