Lowering the carbon nanotube (CNT) fabrication temperature (&lt;450oC) could reduce or alleviate the principal environmental impact (emissions and energy in manufacture) associated with this important class of nanomaterials. Furthermore, lower synthetic temperatures would enable CNT production on CMOS-compatible substrates and other low-melt temperature materials, enabling important medical, aerospace, and electronic applications. The equilmolar C2H2-CO2 reaction has shown promise at low temperature and with various functional catalyst materials; however, the role of CO2 is not fully understood. Here, we explored the role of CO2 experimentally and theoretically. In particular, 13C labeling of CO2 coupled with Raman spectroscopy demonstrated that CO2 is not an important C source material in nanotube growth (at 710oC, 12CO2-CNTs and 13CO2-CNTs have D and G bands that are statistically indiscernible, D-bands at 1322.6±2.7 cm-1 and 1322.3±3.8 cm-1, respectively, and G-bands at 1594.7±3.6 cm-1 and 1593.7±4.5 cm-1, respectively). Furthermore, the absorption behaviors of C2H2 and CO2 on graphene cluster were investigated through density functional theory (DFT) calculation, and these computational results support the observation that CO2 carbon does not interact with a graphene-like surface. The binding energies of C2H2 (4.83-9.08 eV) were far higher than the binding energies of CO2 (0.03-0.46 eV), suggesting the former is more likely to add to a growing graphitic structure. Nevertheless, the promoting role of CO2 in CNT growth has been commonly observed, and we propose a CO2-assisted dehydrogenation could occur to remove H atoms in the growing CNT lattice. Lastly, we measure volatile organic compound (VOC) emissions during the process and compare the synthetic emission and energy requirements in CO2-assisted growth with more traditional acetylene-fed processes.

Role of CO2 in the equimolar C2H2-CO2 reaction to synthesize carbon nanotubes: environmental and mechanistic implications

249th National Meeting (2015)

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