DWNTs

Finally, Eklund s group has described double-walled nanotubes (DWNT), with ca. 0.7 nm inner diameter and 1.4 nm outer diameter, that can form a three-layer cylindrical capacitor with a shell of bromine anions forming the outer electrode. Holes segregate on the outer nanotube, and saturation bromine doping creates 1 hole per 26 carbon atoms in the DWNT [135]. 

Double-stranded RNA (dsRNA) in yeast, 26 451—452 Double-stranded RNA viruses, 3 135 Double-suction pumps, 21 60, 63 Double tipping pan vacuum filter, 11 352 Double titration method, 15 145 Double vacuum-arc remelting (VAR), in titanium sponge consolidation, 24 854 Double wall nanotubes (DWNT), 26 737 Double-wall tanks, 24 296 Doubly smart block copolymers,... 

Abbreviations PDT, Photodynamic therapy EPR, Enhanced permeability and retention IHF, Tetrahydrofuran UV, Ultraviolet DNA, Deoxyribonucleic acid PL, Photoluminescence SWNT, Single-walled nanotube DWNT, Double-walled nanotube MWNT, Multi-walled nanotube IV, Intravenous HSP, Heat shock protein ... 

Carbon nanotubes can have one, two, or many sidewalls and are referred to as single-, double-, or multi-walled nanotubes (SWNT, DWNT, or MWNT). Nanotubes can be metallic, or semi-conducting depending on the chirality of the tube. Single-walled nanotubes (SWNT) are about 1 nm in diameter, and hundreds of nanometers long, whereas multi-walled nanotubes (MWNT) are like nested... 

A single-walled carbon nanotube (S WNT) is a single graphene sheet rolled up in a seamless cylinder, whose diameter is of the order of few nanometers (Fig. 4.12). A double-walled carbon nanotube (DWNT) consists of rolled two graphene layers, and a multiwall carbon nanotube (MWNT) exhibits several co-axial rolls of graphene sheets, one sitting in each other and separated by about 0.35 nm. 

SWNTs single-walled nanotubes DWNTs double-waUed nanotubes MWNTs multi-walled nanotubes CNTs carbon nanotubes not purified... 

As is known, surface area of carbon nanotubes, with some assumptions, interrelates with its diameter and number of walls [10]. Taking into account these data, one cat estimate average number of walls to be 2.8 at CNT diameter near 10 nm and surface area 500 m2/g. These parameters are close to reported for doublewall CNT samples containing 50% DWNT produced by Shenzhen NTP (China). 

Double-walled carbon nanotubes (DWNTs), first observed in 1996, constitute a unique family of carbon nanotubes (CNTs). -2 DWNTs occupy a position between the single-walled carbon nanotubes (SWNTs) and the multiwalled carbon nanotubes (MWNTs), as they consist of two concentric cylinders of rolled graphene. DWNTs possess useful electrical and mechanical properties with potential applications. Thus, DWNTs and SWNTs have similar threshold voltages in field electron emission, but the DWNTs exhibit longer lifetimes.3 Unlike SWNTs, which get modified structurally and electronically upon functionalization, chemical functionalization of DWNTs surfaces would lead to novel carbon nanotube materials where the inner tubes are intact. The stability of DWNTs is controlled by the spacing of the inner and outer layers but not by the chirality of the tubes 4 therefore, one obtains a mixture of DWNTs with varying diameters and chirality indices of the inner and outer tubes. DWNTs have been prepared by several techniques, such as arc discharge5 and chemical vapor depo-... 

Figure 1. HRTEM images of (a,b) undoped DWNTs, (c) N-doped DWNTs using ammoniar (d) N-doped DWNTs using pyridine, and (e,fl of B-doped DWNTs.

The various DWNTs have been characterized with respect to composition and structure. In particular, the effect of B- and N-doping on the dimensions of the nanotubes has been examined by Raman spectroscopy. 

While the decomposition of the CH + Ar over the Mo0, Fe09Mg13O catalyst at 950 °C yielded undoped DWNTs, decomposition of the CH + N H3 + Ar and CH4 t- pyridine E Ar mixtures gave nitrogen-doped DWNTs. Decomposition of the CH + BH3 + Ar mixture over the catalyst at 950 °C yielded boron-doped DWNTs. The N- and B-doped DWNTs could not be produced at temperatures lower than 950 °C. The combustion method employed for the preparation of the catalyst seems to... 

We have used both transmission electron microscopy (TEM) and Raman spectroscopy to characterize the different DWNTs samples. TEM allows direct imaging of the DWNTs and gives indications for the presence of other species along with the DWNTs. In the TEM images, we seldom encountered SWNTs or MWNTs. Besides providing information on the nature and dimensions of DWNTs, Raman spectroscopy helps to characterize the purity and quality of the DWNTs. Electron energy loss spectroscopy (EELS), carried out in a high-resolution electron microscope, and X-ray photoelectron microscopy have been employed to determine the elemental composition of the DWNTs. 

Figure 2. (a) C Is and N 1s XPS signals of N-doped DWNTs prepared using ammonia, ib) C Is and Bis signals of B-doped DWNTs. 

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