Photochemical modification of single-walled carbon nanotubes
using HPHMP photoinitiator for enhanced organic solvent
dispersion
Mirza Nadeem Ahmad
•
Maria Nadeem
•
Yuhong Ma
•
Wantai Yang
Received: 10 November 2009 / Accepted: 14 May 2010 / Published online: 3 June 2010
Ó Springer Science+Business Media, LLC 2010
Abstract Photochemical modification of single-walled
carbon nanotubes (SWCNTs) was carried out by covalent
attachment of 2-propanol-2-yl radicals on the surface of
SWCNTs, which were engendered by the photolysis of
1-[4-(2-Hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-pro-
pane-1-one (HPHMP) under ultraviolet (UV) light. Pristine
single-walled carbon nanotubes (p-SWCNTs) were dis-
persed in acetone along with HPHMP photoinitiator. After
that, the mixture was irradiated by UV light to generate the
free radicals which were introduced onto the surface of
SWCNTs. The modification of SWCNTs was supported
by UV/visible spectroscopy, Fourier transform infrared
spectroscopy (FT-IR), Raman spectroscopy, thermal
gravimetric analysis–mass spectrometry (TGA–MS), and
transmission electron microscopy (TEM). UV/visible
results revealed the loss of van Hove singularities due to
covalent modification. The modification was further veri-
fied by FT-IR showing the signals at 3421 and 1100 cm
-1
due to stretching and bending of O–H group, respectively.
Moreover, other peaks at 2927 and 2858 cm
-1
indicated
the asymmetric and symmetric stretching modes of ali-
phatic C–H bond, respectively. Raman spectra illustrated
that the intensity ratio of the tangential mode to the dis-
order mode (I
G
/I
D
), for modified SWCNTs (F-SWCNTs),
decreased nearly four times than p-SWCNTs. TGA–MS
also evidenced the signal corresponding to m/z 59 at
400 °C indicating the presence of 2-propanol-2-yl groups.
TEM and dispersibility data demonstrated that the sidewall
modification detached the bundled structure, enhanced the
dispersion in common organic solvents and retained the
original size of SWCNTs without hefty modification,
which could cut or damage the nanotubes.
Introduction
Since their discovery, carbon nanotubes have attracted a
great deal of interest, not only in scientific fields but also in
the field of nanotechnology applications, such as electronic
devices, energy-related applications [1], and fiber rein-
forcement materials in polymer matrix composites [2].
A single-walled carbon nanotube (SWCNT) is unique
among solid state materials in that every atom is on the
surface [3]. SWCNTs are known as strikingly inert mate-
rials, which due to van der Waals attractive interactions are
usually present in the form of bundles [4]. The SWCNT
sidewalls are largely defect-free and therefore, rather inert
to chemical attack during reactions. Limited reactivity
occurs at defects on the sidewalls generated by curvature-
induced stresses due to non-planar sp
2
carbons and the
misaligned orbitals, and at dangling bonds located at the
tube ends. Chemical modification of SWCNTs is critical
for the applications of nanotubes. Because, the insoluble
SWCNTs are rendered soluble, resulting in easy and effi-
cient chemical processibility [5].
The progress in this field of SWCNT research has been
limited up to now, and the main reason is the poor dis-
persion of SWCNTs in solvents. Then, the modification of
SWCNTs is advantageous because functional groups can
prevent the aggregation of nanotubes and in addition favor
their dispersion in organic solvents [6, 7]. The attached
M. N. Ahmad Á M. Nadeem Á Y. Ma Á W. Yang (&)
State Key Laboratory of Chemical Resource Engineering
and College of Materials Science and Engineering, Beijing
University of Chemical Technology, Beijing 100029,
People’s Republic of China
e-mail: yangwt@mail.buct.edu.cn
M. N. Ahmad
e-mail: pioneerravian@yahoo.com
123
J Mater Sci (2010) 45:5591–5597
DOI 10.1007/s10853-010-4621-2