Stacking carbons

Only a few in vivo dermal toxicity studies have been reported so far. Huczko and Lange [50] evaluated the potential of raw CNTs to induce skin irritation by conducting two routine dermatological tests (patch test on 40 volunteers with allergy susceptibilities and Draize rabbit eye test on four albino rabbits). Koyama etal. [51] showed the biological responses to four different types of carbon nanotubes (SWNTs, two types of MWNTs with different diameters, and cup-stacked carbon nanotubes) after their subcutaneous implantation in mice. Both tests [50, 51] showed no or poor irritation effects. However, the in vitro studies in epidermal cell lines exposed to CNTs, and also a more recent report on the toxic outcomes of topical exposure of mice to SWNTs [46], have raised concerns over these assessments. Clearly, this is an area requiring further scientific evaluation. 

Methods of electron spectroscopy are widely used to follow the electron-transfer process. Thus, the progress of electron transfer from naphthalene anion-radical to cup-stacked carbon nanotubes is easily detected by monitoring the UV absorption spectrum. Namely, the absorption band around 500-900 nm due to naphthalene anion-radical completely disappears after reduction of the nanotubes. At the same time, the reduced nanotubes exhibit ESR spectrum characterized with g-factor of 2.0025 (Saito et al. 2006). This g-value is close to the free spin g-factor of 2.0023 that is diagnostic of the delocalized electron on carbon nanomaterials (Stinchcombe et al. 1993). It should be parallelly... 

Electron diffraction analysis for these carbon tubes revealed that the tube wall consists of cylindrically stacked carbon layers. The lattice image for the carbon tubes with a diameter of 30 nm is shown in Figure 10.1.7, where at least four tubes cross each other. The thickness of the walls is about 10 nm, and consequently the carbon has a hollow with a diameter as small as 10 nm. Many small lines, which correspond to 002 lattice planes, are observed in the cross section of the walls for each tube. 

Waje, M.M. et al.. Durability investigation of cup-stacked carbon nanotubes supported Pt as PEMFC catalyst, FCS Trans., 3, 677, 2006. 

Fig. lO Schematic representation of randomly stacked carbon layers with statistically distributed nestled AsF " ions... 

Figure 3.29 Cup-stacked carbon nanotubes consist of individual truncated cones. Model of a cup-stacked CNT (a) and HRTEM-image of these nanotubes (b) ( AlP 2002).

Nevertheless, classical heterogeneous catalysts like particulate noble metals may be immobilized on the nanotube surface as well. Nanoparticles of platinum or rhodium, for instance, can be deposited on cup-stacked carbon nanotubes by reductive precipitation (Figure 3.114b). The catalysts obtained this way suit an application in fuel cells run on methanol. Electrodes made from the nanotube material exhibit twice the efficiency as compared to the classical material XC-72-carbon. The particles of noble metal on the nanotube surface catalyze the direct conversion of methanol into CO2 (MeOH -1- H2O CO2 -1- 6 H -1- 6e ). A material to be employed in such fuel cells has to meet some essential requirements, including a maximal specific surface, a defined porosity and a high degree of crystalhnity. Carbon nanotubes are endowed with exactly these characteristics, which is why they are the most suitable material for electrodes. Their high price, however, is still prohibitive to an industrial scale application. 

Zhang, H. X., Feng, C., Zhai, Y. C., Jiang, K. L., Li, Q. Q., and Fan, S, S. [2009]. Cross-stacked carbon nanotube sheets uniformiy loaded with SnOj nanoparticles a novel binder-free and high-capacity anode material for lithium-ion batteries,i4dv. Mater., 21, pp. 2299-2304. 

Figure 6.2 Some narrow gap, "parallel plate" cell geometries, (a) The Monsanto vertical plate stack (b) The BASF stacked carbon disc cell (c) A cylindrical cell (d) A zero-gap membrane cell.

Matter et al. [129] and Maldonado and Stevenson [116] attributed the catalytic activity to pyridinic nitrogen atoms at edge-planes of cub-stacked carbon nanotubes [129] and carbon nanofibers [116], respectively. The authors proposed that the present metal only enhances the integration of active pyridinic nitrogen atoms. 

We will determine if there are systematic and predictable chemical relationships between the vertically stacked carbonate cementation/decemen-tation zones, and the relationship between organic acids and carbonate mineral stability. 

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