Stephen C. Hawkins

Recent Developments in Carbon Nanotube Membranes for Water Purification and Gas Separation

Carbon nanotubes (CNTs) are nanoscale cylinders of graphene with exceptional properties such as high mechanical strength, high aspect ratio and large specific surface area. To exploit these properties for membranes, macroscopic structures need to be designed with controlled porosity and pore size. This manuscript reviews recent progress on two such structures: (i) CNT Bucky-papers, a non-woven, paper like structure of randomly entangled CNTs, and (ii) isoporous CNT membranes, where the hollow CNT interior acts as a membrane pore. The construction of these two types of membranes will be discussed, characterization and permeance results compared, and some promising applications presented.

Durability and inflammogenic impact of carbon nanotubes compared with asbestos fibres

BackgroundIt has been suggested that carbon nanotubes might conform to the fibre pathogenicity paradigm that explains the toxicities of asbestos and other fibres on a continuum based on length, aspect ratio and biopersistence. Some types of carbon nanotubes satisfy the first two aspects of the fibre paradigm but only recently has their biopersistence begun to be investigated. Biopersistence is complex and requires in vivo testing and analysis. However durability, the chemical mimicking of the process of fibre dissolution using in vitro treatment, is closely related to biopersistence and more readily determined. Here, we describe an experimental process to determine the durability of four types of carbon nanotubes in simulated biological fluid (Gambles solution), and their subsequent pathogenicity in vivo using a mouse model sensitive to inflammogenic effects of fibres. The in vitro and in vivo results were compared with well-characterised glass wool and asbestos fibre controls.ResultsAfter incubation for up to 24 weeks in Gambles solution, our control fibres were recovered at percentages consistent with their known in vitro durabilities and/or in vivo persistence, and three out of the four types of carbon nanotubes tested (single-walled (CNTSW) and multi-walled (CNTTANG2, CNTSPIN)) showed no, or minimal, loss of mass or change in fibre length or morphology when examined by electron microscopy. However, the fourth type [multi-walled (CNTLONG1)] lost 30% of its original mass within the first three weeks of incubation, after which there was no further loss. Electron microscopy of CNTLONG1 samples incubated for 10 weeks confirmed that the proportion of long fibres had decreased compared to samples briefly exposed to the Gambles solution. This loss of mass and fibre shortening was accompanied by a loss of pathogenicity when injected into the peritoneal cavities of C57Bl/6 mice compared to fibres incubated briefly. CNTSW did not elicit an inflammogenic effect in the peritoneal cavity assay used here.ConclusionsThese results support the view that carbon nanotubes are generally durable but may be subject to bio-modification in a sample-specific manner. They also suggest that pristine carbon nanotubes, either individually or in rope-like aggregates of sufficient length and aspect ratio, can induce asbestos-like responses in mice, but that the effect may be mitigated for certain types that are less durable in biological systems. Results indicate that durable carbon nanotubes that are either short or form tightly bundled aggregates with no isolated long fibres are less inflammogenic in fibre-specific assays.

Carbon nanotube modified carbon composite monoliths as superior adsorbents for carbon dioxide capture

Carbon composite monoliths were prepared from a commercial phenolic resin mixed with just 1 wt% of carbon nanotubes (CNTs) followed by carbonization and physical activation with CO2. The products possess a hierarchical macroporous–microporous structure and superior CO2 adsorption properties. In particular, they show the top-ranked CO2 capacity (52 mg CO2 per g adsorbent at 25 °C and 114 mmHg) under low CO2 partial pressures, which is of more relevance for flue gas applications. This matches or exceeds those of carbons produced by complex chemical activation and functionalization. Our study demonstrates an effective way to create narrow micropores through structural modification of carbon composites by CNTs.

Carbon Nanotube Webs: A Novel Material for Sensor Applications

Since their discovery in 1991 by Iijima, [ 1 ] carbon nanotubes (CNTs) have attracted intensive research and investigation due to their unique electrical, mechanical, structural, and chemical properties. [ 2 , 3 ] Their novel properties make them attractive for fabricating electrochemical sensors and biosensors. Several compounds have been reported to undergo improved electrochemical reactions at the CNT surface, such as cytochrome c, [ 4 ]

Aligned silane-treated MWCNT/liquid crystal polymer films

We report on a method to preferentially align multiwall carbon nanotubes (MWCNTs) in a liquid crystalline matrix to form stable composite thin films. The liquid crystalline monomeric chains can be crosslinked to form acrylate bridges, thereby retaining the nanotube alignment. Further post-treatment by ozone etching of the composite films leads to an increase in bulk conductivity, leading to higher emission currents when examined under conducting scanning probe microscopy. The described methodology may facilitate device manufacture where electron emission from nanosized tips is important in the creation of new display devices.

Enhanced mechanical performance of CNT/Polymer composite yarns by γ -irradiation

Multiwall carbon nanotube (CNT) spun yarns were subjected to γ-irradiation in an oxygen rich environment, followed by the application of epoxy to form CNT/epoxy composite yarns with a high CNT fraction. The method for fabrication of the CNT/polymer composite yarns was presented, and the effect of γ-irradiation on the mechanical performance of the pure CNT spun yarns and their epoxy composite yarns were studied. The γ-irradiated CNT yarns were also characterized by X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results of this study have demonstrated that the γ-irradiation is an effective micro-engineering tool to improve mechanical properties of the CNT spun yarn and its epoxy composite yarn.

Dry Drawn Multiwall Carbon Nanotube Sheet as a Counter Electrode for Dye-Sensitized Solar Cells: Multilayer Optimization

We demonstrate the fabrication of dye sensitized solar cells using multiwall carbon nanotube (MWNT) sheets as a counter electrode with catalytic activity optimized by layering as an alternative to platinum deposited on fluorinated tin oxide (FTO). The sheets are drawn directly from a highly aligned forest of MWNTs grown on silicon by chemical vapor deposition. We used different number of MWNT layers on the FTO and pure glass. Cell performance was found to vary with the number of MWNT sheets. When using of 10 or more layers we can substitute the FTO with platinum catalytic particles.

Introduction to Fiber Materials

Abstract The nature of fiber materials and the differences between conventional fibers and nanoscale fibers are discussed in this chapter. The challenge of carbon nanotube (CNT) yarn fiber fabrication is provided from the perspective of conventional yarn fiber fabrication. Prospects for large-scale manufacturing and the physical properties of yarn are also discussed. This chapter sets the stage for presentation of a compendium of techniques working toward producing superfiber materials.

Impact of Carbon Nanotube Aspect Ratio and Dispersion on Epoxy Nanocomposite Performance

This paper compared the effect of aspect ratios and dispersions of carbon nanotubes (CNT) made in CSIRO, with a broad range of aspect ratios with similar dimensions in diameter, on the electric conductivity, rheology and dynamic mechanical thermal analysis of multi-wall nanotubes (MWNT)/epoxy nanocomposites. A medium aspect ratio seems to be the most effective in conductive network formation in epoxy matrix and also provide best storage modulus of CNT/epoxy nanocomposites under providing processing conditions.