Macroscopic shaping of carbon nanotubes with high specific surface area and full accessibility (original) (raw)
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Chemistry: A European Journal, 2001
The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO 3) 3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged twodimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energyloss spectroscopy (EELS)). From Mössbauer studies, the presence of two different oxidation states (Fe 0 and Fe III) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laserstructuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the mm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.
Novel supported catalytic materials based on multiwalls carbon nanotubes
2011
In this work is presented a method that allows proper control of the nanoscale curvature of the external surface in multiwall carbon nanotubes (MWCNT), and shown its effect on the properties of Ni/MWCNT catalyst. After removal of residual nickel by treatment with HNO3 the external surface of parent CNT's was decorated with 15-17 nm nanoparticles of CaCO3 (25 wt.%) by carbonization of deposited Ca-nitrate. The followed partial catalytic aircombustion of CNT's at conversions 30-50% modified the morphology of their walls. After removal of CaCO3 catalyst by treatment of the CNT's surface with HNO3 the modified nanotubes were decorated with metallic nickel by sonochemical deposition. The partial combustion of carbon constituting the CNT walls catalyzed by CaCO3 nanoparticles converts their structure from parallel grapheme layers to aggregates formed by grapheme onions with diameter of 5-12 nm. The nickel nanoparticles were located exclusively at the onions tops due to increas...
Synthesis of single- and multi-wall carbon nanotubes over supported catalysts
Applied Physics A-materials Science & Processing, 1998
Catalytic synthesis and some characterization of multi-and single-wall carbon nanotubes are presented. Supported transition-metal catalysts were prepared by different methods and were tested in the production of nanotubes by decomposition of hydrocarbons at 700 • C, using a fixed-bed flow reactor.
Carbon, 2008
Double-walled carbon nanotubes (DWCNTs) were prepared from methane using a Fe/MgO porous catalyst. A series of catalyst powders with different pore size distributions were obtained by compression at pressures of 0-233 MPa. These were used to decompose methane and synthesize DWCNTs which differed in activity, purity, yield and degree of perfection. Characterization by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermo-gravimetric analysis, N 2 adsorption measurement (Brunauer-Emmett-Teller (BET)) and Hg penetration provided direct evidence that a compact catalyst structure is not good for the nucleation and growth of DWCNTs, e.g., a catalyst with a compact structure that did not have pores larger than 30-50 nm mostly produced multi-walled carbon nanotubes. The confined growth and buckling model of DWCNTs inside the porous catalysts are proposed to explain the growth behavior. These results suggest that a porous catalyst for DWCNT synthesis should have a large pore size distribution or loose stacked structure, which provides new guidelines for catalyst design.
Chemical Physics Letters, 2000
Multi-wall carbon nanotubes have been produced by the catalytic decomposition of acetylene. Co–Mo, Co–V and Co–Fe mixtures supported either on zeolite or corundum alumina were used as catalysts. When Fe or V is added to Co, the carbon deposit increases. The nanotubes were characterized by both low and high resolution TEM. From histograms representing the outer diameter distributions, it is clear that the outer diameter of the nanotubes can be controlled by choosing the appropriate catalyst.
Synthesis of a carbon nanotube monolith with controlled macroscopic shape
Carbon, 2006
Multi-walled carbon nanotubes (MWCNTs) have recently received increasing interest due to their exceptional physical and chemical properties . During their growth, MWCNTs are highly entangled and interconnected, forming a dense and elastic network generally on a microscopic scale which renders their direct use complicated because of their fluffy character. Thus, a post-synthesis treatment is necessary to obtain a macroscopic shape. Most of the works on macroscopic shaping of carbon nanotube samples have been devoted to the synthesis of macroscopic fibers of either single-walled or multi-walled carbon nanotubes by adding foreign agents to the nanotubes or by modifying the synthesis method . However, almost no process is dealing with the one-step synthesis of such samples.