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The use of aliphatic alcohol chain length to control the nitrogen type and content in nitrogen
doped carbon nanotubes
George Bepete,a Zikhona N. Tetana,a Susi Lindner,b Mark H. Rümmeli,b Zivayi Chiguvarea and Neil J.
Covillea
aDST/NRF Centre of Excellence in Strong Materials and Molecular Sciences Institute, School of
Chemistry, University of the Witwatersrand, WITS 2050, Johannesburg, South Africa
bLeibniz
Institute of Solid State and Materials Research, P. O. Box 270116, D-01171, Dresden,
Germany
[email protected]
Abstract
The nitrogen in N-CNTs can exist in a variety of oxidation states, the most important being the pyridinic
type N and the quaternary N. Optimization of each type of N is important if the respective properties
brought about by each type of N species are to be utilized in applications. To this end, we have
synthesized a range of N-CNT materials using an ethanol/acetonitrile reactant mixture pyrolysed at
different CVD synthesis temperatures and alcohol/acetonitrile mixtures with aliphatic alcohols with
different chain length (ROH; R = CH3, C2H5, C4H9, C5H11, C7H15 and C8H17) to determine if the N
incorporated can be influenced by temperature or oxygen content in the precursor. The C/N ratio in the
precursor mixture of each different alcohol increased with increase in alcohol chain length, for example
from 7.1 for a methanol/acetonitrile mixture to 12.6 for an octanol/acetonitrile mixture. XPS analysis of
the CNTs produced from an acetonitrile/ethanol mixture using different CVD temperatures (700 – 1000
oC), revealed that nitrogen incorporation in N-CNTs decreased with an increase in CVD temperature
and that the type of nitrogen species incorporated also varied. Molecular nitrogen and a low content of
pyridinic nitrogen was obtained in N-CNTs grown at 700 oC and 800 oC, while quaternary nitrogen was
noted in all N-CNTs grown. The N content in the N-CNTs grown at 850 oC increased with the alcohol
chain length and also controlled the nitrogen species incorporated, an effect related to the oxygen
content of the reactant mixtures.
References
[1] Bepete G.; Tetana ZN.; Lindner S.; Rümmeli MH.; Chiguvare Z.; Coville NJ. Carbon, 52 (2013), 316325.
Figures
Nitrogen Content in N-CNT product %
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1
2
3
4
5
6
7
8
9
Aliphatic alcohol carbon chain length
Figure 1. The N composition in N-CNTs made from the different alcohol precursor mixtures obtained
from XPS analysis.
Methanol/acetonitrile N1s
(a)
Quaternary
401.2 eV
408
406
404
402
400
Molecular N
Intensity (a.u.)
Intensity (a.u.)
Molecular N
404.9 eV
Ethanol/acetonitrile N1s
(b)
398
(404.6 eV)
408
406
Binding energy (eV)
406
404
400
408
396
Intensity a.u.
406
406
404
402
402
400
Binding energy (eV)
400
398
396
Octanol/acetonitrile N1s
(f)
Pyrrolic N
400.8 eV
Pyridinic N
398.7 eV
408
404
Binding Energy (eV)
398
Pyrrolic N
400.9 eV
Intensity (a.u.)
Intensity (a.u.)
Molecular N
404.8 eV
Pyridinic N
398.6 eV
Molecular N
404.8 eV
Intensity a.u.
398
Heptanol/acetonitrile N1s
Quaternary N
401.7 eV
398
Pentanol/acetonitrile N1s
Binding Energy (eV)
(e)
400
Quaternary N
401.3 eV
Pyridinic N
398.4 eV
402
402
(d)
Quaternary N
401.2 eV
Molecular N
404.3 eV
408
404
Binding Energy (eV)
Butanol/acetonitrile N1s
(c)
Quaternary N
(401.2 eV)
396
Quartenary N
401.7 eV
Pyridinic N
398.7 eV
Molecular N
404.8 eV
408
406
404
402
400
398
396
Binding energy (eV)
Figure 2. XPS N1s spectra of N-CNTs produced in CVD at 850 oC showing different types of nitrogen incorporated in
N-CNTS when (a) methanol, (b) ethanol, (c) butanol, (d) pentanol, (e) heptanol, and (f) octanol were used in the
precursor.