Nanotubes formation

Yuwono VM, Hartgerink JD (2007) Peptide amphiphile nanofibers template and catalyze silica nanotube formation. Langmuir 23 5033-5038... 

Figure 10.8 Nanotube formation upon introducing a c/s-double bond in a diaminopyridine alkylamide and their corresponding alkyl chain packing in DAP-2. Reprinted with permission from [75] (2004) American Chemical Society.

John, G., Masuda, M., Okada, Y., Yase, K. and Shimizu, T. (2001) Nanotube formation from renewable resources via coiled nanofibers. Advanced Materials, 2001, 13, 715-718. 

Gorbitz, C. H. (2001). Nanotube formation by hydrophobic dipeptides. Chemistry 7, 5153-5159. 

The following mechanism has been proposed for titania nanotube formation by Bavykin and co-workers [94] ... 

Nanotube arrays several microns in length can be fabricated using KF (or NaF with identical results) electrolytes of variable pH [22], a summary of which is presented in Table 5.3. Prior to KF addition, the desired pH was obtained by adding NaOH, sulfuric acid (pH 1-2), sodium hydrogen sulfate, or citric acid (pH 2.5-7.5). The F concentration was held fixed at 0.1 mol/L. In 0.1 mol/L F and 1 mol/L H2SO4 medium, the potential window for nanotube formation is 10-25V (Samples 01 to 08). Outside of this potential range no nanotubes were formed (Samples 01 and 08). In Sample... 

To help understand the process of nanotube formation, FESEM images of the surface of the samples anodized at 20 V for different durations were taken and analyzed. At the start the anodization the initial oxide layer [111], formed due to interaction of the surface Ti ions with oxygen ions (0 ) in the electrolyte, can be seen uniformly spread across the surface. The overall reactions for anodic oxidation of titanium can be represented as... 

In formamide electrolyte containing fluoride ion, the starting anodization current does not drop instantly as observed in aqueous bath. The gas evolution which is indicative of electronic conduction was observed at the anode. The anodization current drops steeply thereafter due to the initial formation of an insulating oxide layer, see Fig. 5.10. In this region, electronic conduction decreases due to the blocking action of the formed oxide, and ionic conduction increases. Once the oxide layer is completely formed over the entire exposed surface of the anode, electronic conduction becomes negligible and ionic conduction dominates the mechanistic behavior. Nanotube formation reduces the surface area available for anodization with a correlated decrease in current density, while deepening of the pore occurs. 

A similar type of macrocycle stacking leading to the nanotube formation was recently reported by the Stoddart group [44b]. The latter authors synthesized cyclodextrins analogues 96 built of alternating D- and L- sugar units. The... 

In addition to calcium, we note that divalent manganese and zinc and trivalent aluminium can also induce a-lactalbumin nanotube formation. By using these ions instead of calcium at R = 3, transparent gels (see... 

Micrographs of TiC>2 nanotubes from TBOT revealed similar shapes and dimensions [18]. The Ti02 nanotube formation is accompanied by small amounts of non-structured titania. Even at 203 K hydrolysis and condensation of TBOT run too fast to avoid the formation of this side-product completely. 

Nagano, T., Ishikawa, Y., and Shibata, N. Effects of surface oxides of SiC on carbon nanotube formation by surface decomposition. Jpn. J. Appl. Phys. 42, 2003 1380-1385. 

Lopez P.N., Ramos I.R., Ruiz A.G. A study of carbon nanotube formation by C2H2 decomposition on an iron based catalyst using a pulsed method. Carbon, 2003,41(13), 2509-2517. 

Fig. 13 Comparison of the naphthyl proton signals observed in the H-NMR spectrum of molecule 12 in (a) CDC13 + MeOD NDI core contains two distinct sets of protons (blue and red) and (b) CDC13 nanotube formation further differentiates the blue and red NDI protons as non hydrogen-bonded (H ) and hydrogen-bonded (H) [17]...

Ponnuswamy N, Pantog GD, Smulders MMJ, Sanders JKM (2012) Thermodynamics of Supramolecular Naphthalenediimide Nanotube Formation The Influence of solvents, side-chains and guest templates. J Am Chem Soc doi 10.1021/ja2088647... 

Yasuda, A. Kawase, N. Matsui, T. Shimidzu, T. Yamaguchi, C. Matsui, H. Carbyne electrochemical preparation and nanotube formation. Reactive Funct. Polymers 1999, 41. 13-19. 

Therefore, multiwalled carbon nanotubes may henceforward be assumed normally to consist of concentric single-walled tubes. These are largely independent of one another and may belong to different structural types even within an individual MWNT. However, this does not mean that alternative structures do not exist. At least partially coiled species have been observed in some cases, and rolled up graphene layers play an important role in some hypotheses on the mechanism of nanotube formation. 

The mechanism of nanotube formation in chemical vapor deposition features characteristics rather distinct from those found for the synthesis by arc discharge or laser ablation. Contrary to the latter, a solution of small carbon clusters in and subsequent diffusion through catalyst particles play a minor role in the deposition from the gas phase. The employed hydrocarbons decompose directly on the surface of the catalytic particle. The carbon, therefore, becomes immediately available for nanotube growth. 

It is conceivable that a parallel bundle of linear polyyne chains (the carbon allotrope named chaoite or carbyne) may form, via thermally-allowed (4 + 2)-n-electron cycloadditions, six-membered rings which lead to graphene sheets and/or nanotubes. However, the mechanism of nanotube formation in a plasma produced by arc discharge appears to require the presence of a transition metal atom at the rim of the growing nanotube [77 j. 

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