Use of Saccharides as Solid-state Precursors for the Synthesis of Carbon Nanotubes
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Use of Saccharides as Solid-state Precursors for the Synthesis of Carbon Nanotubes Gokce Kucukayan1, Serim Kayacan1, Beril Baykal2, and Erman Bengu2 1 Institute of Materials Science and Nanotechnology, Bilkent University, Ankara, Turkey 2 Chemistry, Bilkent University, Department of Chemistry, Ankara, Turkey ABSTRACT Saccharides, ranging from simple table sugar (sucrose) to lactulose were successfully used as solid-state precursors for the synthesis of multi-walled carbon nanotubes (MWCNT). Dehydrated saccharide residues mixed with catalyst powders were subjected to pyrolysis at high temperatures (up to 1300°C) under flowing Argon atmosphere. Pyrolysis products were investigated using TEM, SEM, Raman spectroscopy and EDS. Images taken using the S/TEM and bright field mode of TEM showed the presence of helical multi-walled carbon nanotube (HMWCNT) and regular MWCNT formation. More than two or three catalyst particles were observed to be present inside the hollow core of some of the nanotubes synthesized, suggesting a high level of capillary activity inside the tubes during synthesis. INTRODUCTION Since, carbon nanotubes (CNT) were discovered1, they continue to attract more and more attention of scientists from diverse fields of science because of their unique structural, mechanical, and electronic properties2. Potential applications of CNTs range from semiconductors, chemical sensors to structural composites3. Presently, there are three main techniques being used as synthesis methods for CNTs; these are arc discharge4, laser ablation5 and chemical vapor deposition (CVD) 6. Although, CNTs can be easily synthesized by these techniques and their variants in a laboratory environment, scaling up the CNT synthesis for high volume manufacturing utilizing these does pose some disadvantages, such as upfront capital costs, running costs, process/quality control and yield7. For instance, for the arc discharge method necessary precursor purity and quantity are high8. Small amount of sulfur presence has been suggested to promote CNT growth and enhance yield of synthesis process used in some studies9,10. In an earlier study, Katsuki et al11 reported higher carbon fiber yields for cases when sulfur and iron were used together in comparison to runs where only one was used. Sulfur can be introduced to the synthesis reactor through the use of sulfur containing gas (e.g. H2S) 12, sulfur powder 13, metal compound (e.g. CdS) 14, or as a part of the floating catalyst15. While the exact role of sulfur or the mechanism through which it influences the CNT growth is not very well understood, sulfur has been found to lower the surface tension of metal/carbon interface and improve the growth of carbon nanotube as the metal catalyst flows inside the tube by the capillarity16. Another proposed mechanism through which sulfur may influence CNT growth mechanism is that sulfur aiding the graphitization of carbon below 1700 0 16 C . Hence, there are also cases where with addition of sulfur to catalysts lead to the observation of changes i
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