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Introduction: A step
forward: MgO-based catalysts The images below illustrate the combustion process, the formation of a CNTs-Co-MgO composite powder from the reduction of the Mg 1-xCoxO solid solution and then the extraction of the CNTs using HCl (chosen for being a non-oxidising acid). 
Filling
CNTs with 1D-crystals Metal halides may be introduced (in the melted state) into SWNTs by capillarity. These experiments permit the study of low dimensional crystal growth whereby the incorporated material is constrained by the encapsulating van der Waals surface of the carbon capillaries, to a few atomic layers in thickness. The preparation of highly anisotropic 1D structures confined into SWNTs is one of the key objectives in carbon research, as the introduction of these materials into the hollow nanotubes cavities could result in interesting effects on their physical and electronic properties. Amongst many examples, here is the of TlCl. This salt, which can crystallize both with the Pm3m CsCl-type structure and with the Fm3m rocksalt structure, crystallizes predominantly in the latter form inside SWNTs. In the examples in Figures 1(a) and (b), two examples of (2x2) TlCl crystals formed inside 1.4nm diameter (i.e. conforming to (10,10)) SWNTs are shown. The bilayer crystals image as a continuous array of dark spot pairs forming along the SWNT capillaries, as shown in the lattice images in Figs. 1(a) and (b). The detail in Figure 1(c) shows clearly the microstructure of the incorporated crystal. An image simulation in Figure 1(d) shows that each of the dark spots images with identical contrast which is to be expected because each atom column contains the same pair of atoms in projection (i.e. Tl-Cl or Cl-Tl). The crystallisation behaviour of this material is therefore similar to that of KI, which forms both (2x2) and (3x3) crystals inside SWNTs. As with (2x2) KI crystals observed in 1.4nm (ca. (10,10) SWNTs), lattice distortions were observed in the incorporated crystals. Along the capillaries a d-spacing of ca. 0.32nm was obtained (which corresponds to {200} for bulk TlCl) while across the capillaries, this spacing increased to nearly 0.4nm. Wider SWNTs were also observed incorporated with TlCl, with the rocksalt form predominating although the lattice distortions were less pronounced.  Figure 1. This cubic structure is the simplest one, so the modelization
is not so tricky but with a more complex structure, the results become more
difficult to interpret. The case of PbI2 is a lot more complex
than that observed for TlCl, presumably because this material forms a relatively
more complex structure in the bulk. The P-3m1 layered form of PbI2
is essentially similar to CdCl2 and consists of stacked layers
of edge sharing PbI6 octahedra (Figure 2). This structure was
found to arrange in different ways inside SWNTs and DWNTs according to the
diameter of the confining tubules, as well as the obtained direction of crystal
growth inside their capillaries (Figures 3 to 5). 
Figure 2. Bulk structure of PbI 2 consisting of stacked layers of PbI6 edge sharing octahedron (cf. CdCl2). 
Figure 3. (a) HRTEM image
of a SWNT bundle completely filled with PbI2. (b) Detail
obtained from the boxed region in (a) ; 0.36nm (or {110}) lattice
planes of PbI 2 are clearly visible in two adjacent tubules
on the periphery of the bundle. (c) FFT obtained from a slightly
larger region of bundle than (b). The indicated maxima correspond
to lattice planes apparently related by a mirror plane (however,
the planes occur in adjacent tubules !). (d) HRTEM image of a discrete
SWNT filled with a 1D crystal of PbI2 . (e) Detail from
boxed region in (d), showing arrangement of PbI2 polyhedra,
which appear, as dark spots. (f) and (g) 'best fit' image simulation
and corresponding structural model conforming to a three polyhedral
thick slab of PbI2. Edge terminating PbI5
square pyramids are indicated in red. (h) End on view of SWNT/PbI2
composite showing a 1D chain of PbI6 octahedra bounded
by two 1D chains of reduced coordination PbI5 square
pyramids. In the case of SWNTs, most of the obtained encapsulated 1D PbI2 crystals show a strong preferred orientation with their {110} planes aligning at an angle of ca. 60° to the SWNT axes as shown in Figures 3(a) and (b). Due to the extremely small size of the nanotubule capillaries, individual crystallites were often only a few polyhedral layers think, as outlined in Figures 3(d) to (h). As a result of lattice terminations enforced by capillary confinement, the edge polyhedra must be of reduced coordination, as indicated in Figures 3(g) and (h) (terminating square pyramidal polyhedra are represented in red). This crystal growth behaviour resembles that recently reported for lanthanide halides incorporated within SWNTs. In some cases, capillary confinement gives rise to some interesting folding effects in the incorporated PbI2 crystals, such as that shown in Figure 4. In this case a five-layer thick polyhedral slab of PbI2 is folded about its centre to form a highly strained crystal within the tip of a 2nm SWNT (Figures 4(a)-(f)). As with the example shown in Figure 3, this crystal terminates with square pyramidal polyhedra (Figure 4(g)). 
Figure 4. (a) and (b) two HRTEM
images obtained at different defocus of a PbI2 1D crystal formed
in the tip of a 2nm diameter (ca. (15,15) conformation) SWNT. In enlargement
((c) and (d)) an apparent bend in the crystal is observed. The bend forms
down the middle of the crystallite, as indicated by the arrows in (e) which,
assuming the same general microstructure as in Figure 2, corresponds to a
'folded' slab of PbI2 polyhedra, as indicated in side on projection
in (f) and in end on projection in (g). As with Figures 3(g) and (h), terminating
PbI2 square pyramids are indicated in red. In the case of PbI2 formed inside DWNTs, in general, similar crystal growth behaviour was observed to occur in narrow tubules with comparable diameters to those of SWNTs. However, as the diameter of the incorporating capillaries increased, frequently different preferred orientation was observed, as shown by the example in Figure 5. In this example, the crystal has grown and is viewed with the [121] direction arranged parallel to the direction of the electron beam (Figures 5(a)-(d)). If the SWNT/PbI 2 composite is viewed 'side on' (as indicated by the arrow in Figure 5(e)), it can be seen that polyhedral slabs (cf. Figure 2) are arranged along the capillary oriented at an angle of ca. 45° to the tubule axis. 
Figure 5. (a) HRTEM image of
a DWNT continuously filled with PbI2. The inset FFT indicates
that this crystal is being viewed in a [121] projection. (b) Detail from the
boxed region in (a). (c) shows an image produced by applying an adaptive filter
followed by an inverse Fourier transform to an FFT produced from (b). (d)
'Best fit' image simulation obtained from the structural model in (e) with
the incorporated PbI2 crystallite arranged in a [121] orientation
with respect to the beam direction. (f) If we now look at the DWNT/PbI
2 composite in a 'side on' projection (i.e. in the direction of
the large arrow in (e)), we see that the PbI2 layers (cf. Fig.
2) are arranged at ca. 45º to the tubule axis. The capillary method can be used to grow 1D crystals of different p-block halides in single-walled carbon nanotubes and we have found that the diameter of the host SWNT profoundly influences the obtained structure of the filling material. The reduction of the coordination of the ions in the periphery of the nanotubes, due to the confinement into the capillaries, has been demonstrated and must lead to physical properties different from those of the bulk crystals. This could be especially interesting in the case of PbI2, which exhibits both semiconducting, X-ray imaging and optical properties. Experiments are also under way in our laboratory to investigate the physical properties of these novel composites (coll. LNCMP, Pr J.M. Broto, Dr B. Raquet, Dr M. Sagnes, Dr B. Lassagne, Dr W. Escoffier). Carbon-encapsulated
Co nanoparticles: The precise control of the CCVD parameters also allows the preparation of carbon-encapsulated metal nanoparticles, mainly by adjusting the carbon supply. Here is an example of carbon-encapsulated cobalt nanoparticles (Chem. Mater., 14, (2002), 2553-2558) showing a very high resistance to air oxidation at room temperature (evidenced by magnetic measurements (SQUID))
Localised
growth of Carbon nanotubes: We have developed different strategies to achieve the localised growth of carbon nanotubes on different substrates. We have especially focused our research work on the stamping technique (we developed a new sol-gel ink to be stamped on silicon substrates using a PDMS stamps, see Microelectronic Engineering, 73-74, (2004), 564-569) and more recently on electron-lithography. The main interest of localised-growth is to allow the precise positioning of CNTs on a substrate, avoiding for example the tedious nano-manipulation required for CNTs randomly deposited from a suspension. This is very important in the case of nano-devices and nanoelectronics in particular.
Realising that the localised growth approach does not allow to easily control the nature of the CNTs, we then focused our work on the controled deposition of CNTs on various substrates. After investigating different surface functionalisation strategies, we finally developped a process to print patterns of CNTs on any kind of substrate: after inking (spray deposition), the patterns present on a PDMS stamp can then be transfered to different substrates such as glass, silicon wafers, or flexibles polymer films (Microelec. Eng., 97, (2012), 301-305 (DOI: 10.1016/j.mee.2012.04.011).  We also combined the use of capillary forces (capillary assembly) and dielectrophoresis in order to achieve localised and highly-oriented thin films of DWNTs such as shown below (from Nanotechnology, 23, (9), (2012), 095303:1-7): 
Ceramic-based
nanocomposites High yield synthesis
of DWNTs
 Toxicity
and Ecotoxicity of CNTs
As a conclusion, the huge difference between available CNTs samples (even between different batches made using the same synthesis technique in the case of industrial/commercial sources) makes difficult any comparison and shows that extrapolation is dangerous. This makes the determination of the toxicity threshold of CNTs difficult. More work is needed to understand the mechanisms of toxicity of CNTs and to prevent the toxicity if possible. An important work of characterisation of the tested samples (chemical purity, morphology and structure, composition) is essential if we want to achieve this goal. We have recently been awarded a grant by the French "National Research Agency" (ANR) to suuport our work in this field (2007-2010). A PhD grant was also granted by the Scientific Council of the University Paul Sabatier to study the role of the inflammasome during exposure of macrophages to CNT (2009-2012, with Dr B. Pipy at Rangueil University Hospital). The CIRIMAT is also the French partner of the Marie-Curie Research Training Network (RTN) CARBIO (2006-2010), involving 8 partners from 6 European coutries (Germany, Austria, France, UK, Poland, Netherlands). The aim of this project is tu use functionalised CNTs filled with magnetic materials for selective thermotherapy of cancer cells. The CIRIMAT is a member of the iCEINT International research groupment, dealing with the environmental impact of nanoparticles (collaboration between France and the USA). [a] E. Flahaut et al., Chem.
Commun., (2003), 1442-1443 [b] E. Flahaut et al., Carbon,
44, (6), (2006), 1093-1099 [c] C. Salvador-Morales et al., Molec.
Immun., 43, (3), (2006), 193-201 [d] F. Mouchet et al., Nanotoxicology, 1, (2), (2007),
149-156 [e] F. Mouchet et al., Aquatic Toxicology,
87, (2), (2008), 127-137 Graphene
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Last revision: Aug. 2013
