Carbon Nanotube Bags: Catalytic Formation, Physical Properties, Two-Dimensional Alignment and Geometric Structuring of Densely Filled Carbon Tubes

• Published in: Chemistry : a European journal Vol. 7; no. 13; pp. 2888 - 2895
• Main Authors: Schneider, Jörg J., Engstler, Jörg, Franzka, Steffen, Hofmann, Kathrin, Albert, Barbara, Ensling, Jürgen, Gütlich, Philipp, Hildebrandt, Peter, Döpner, Susanne, Pfleging, Wilhelm, Günther, Bernd, Müller, Günter
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag GmbH 02.07.2001; WILEY‐VCH Verlag GmbH
• Subjects: carbon; catalyst; CVD; iron; nanostructures
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20010702)7:13<2888::AID-CHEM2888>3.0.CO;2-H

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well‐arranged two‐dimensional 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 energy‐loss spectroscopy (EELS)). From Mössbauer studies, the presence of two different oxidation states (Fe0 and FeIII) 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. Laser‐structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the μm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported. An inorganic‐template approach for the synthesis of carbon nanotube (CNT) bags or fibers is reported for the first time. Their tube interior is completely filled with multi‐walled helicoidal CNTs (see illustration). This was made possible by an established catalytic template‐based CVD approach, which entails the use of porous alumina membranes as structure‐ and alignment‐directing compartments.