Novel hybridized SWCNT-PCD: Synthesis and host-guest inclusion for electrical sensing recognition of persistent organic pollutants

Article abstract of DOI:10.1039/c0jm04552g

Fabrication of a hybridized single-walled carbon nanotube (SWCNT) device based on novel sensing material mono-6-deoxy-6-(p-aminophenylamino)-β- cyclodextrin (PCD) via a facile approach has been reported for the first time; moreover, the hybridized materia

Full text of DOI:10.1039/c0jm04552g

Highlighting joint research results from Jinhuai Liu’s
Group, the Research Center for Biomimetic Functional
Materials and Sensing Devices, Institute of Intelligent
Machines, Chinese Academy of Sciences, Hefei, Anhui,
China.
As featured in:
Title: Novel hybridized SWCNT–PCD: synthesis and host–guest
inclusion for electrical sensing recognition of persistent organic
pollutants
The fabricated electrical sensor based on SWCNT-PCD hybrids has been
successfully used for electrical recognition of POPs, displaying excellent
sensitivity and selectivity due to the concept of molecular recognition.
It is reasonable to believe that the hybridized SWCNT-PCD sensor holds
great potential to be developed as a real time environmental monitor.
See L. Kong et al.,
J. Mater. Chem., 2011, 21, 11109.
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PAPER
Novel hybridized SWCNT–PCD: synthesis and host–guest inclusion for
electrical sensing recognition of persistent organic pollutants†
Lingtao Kong, Jin Wang,* Fanli Meng, Xing Chen, Zhen Jin, Mingqiang Li, Jinhuai Liu* and Xing-Jiu Huang*
Received 28th December 2010, Accepted 27th April 2011
DOI: 10.1039/c0jm04552g
Fabrication of a hybridized single-walled carbon nanotube (SWCNT) device based on novel sensing
material mono-6-deoxy-6-(p-aminophenylamino)-b-cyclodextrin (PCD) via a facile approach has been
reported for the first time; moreover, the hybridized material PCD-decorated SWCNTs (SWCNT–
PCD) can be characterized by ultraviolet–visible–near infrared spectroscopy, Raman spectroscopy,
thermogravimetric analysis, field-emission scanning electron microscopy and high resolution
transmission electron microscopy. The PCD-decorated SWCNT devices have been employed to detect
Persistent Organic Pollutants (POPs) on the basis of formation of an inclusion complex with guest
molecules between SWCNT–PCD and POPs, such as 2,4,5-trichlorobiphenyl (TCB), etc. The
significant variation of the electrical conductance of the SWCNT–PCD hybrid corresponding to the
presence of several POPs with different adsorption efficiencies on the surface indicates that the hybrid is
highly sensitive to some specific POP molecules, implying that hybridized SWCNT–PCD has great
potential in application as an environmental monitor. In order to make a quantitative assessment of the
inclusion complexation behavior of PCD with these POP molecules, microcalorimetric titration
experiments and discussions have been carried out.
1
. Introduction
one-dimensional electronic structures and very high surface-to-
13–20
volume ratios.
Unfortunately, the poor sensitivities and
According to the ‘‘Stockholm convention on POPs (persistent
organic pollutants)’’ founded on the United Nations Conference
in 2001, the usage of POPs has been strictly restricted. There-
fore, it is very important to detect and treat POPs, e.g., 2,4,5-
trichlorobiphenyl (TCB), hexachlorobezene (HCB), aldrin,
mirex and chlordane (CD-68), in that these highly noxious
chemicals have been widely-spread in the environment and
accumulated in organisms. Although many detection
selectivities of undecorated SWCNTs severely limit their
application in detection of POPs Therefore, in order to
21,22
improve the sensing performance of SWCNTs,
the func-
tionalization of SWCNTs via physical or chemical approaches
is currently attracting much attention because chemical func-
tionalization can enhance both processibility and sensing
performance of the SWCNTs; moreover, it can improve
dissolution and dispersion of the SWCNTs in various
23,24
1
approaches have been developed, e.g., chromatography, elec-
2
trochemical methods, and surface-enhanced Raman scattering
solvents,
which opens the door to cost-effective methods for
the fabrication of sensors using simple dispensing or printing
techniques.
3
SERS), exploring and developing facile and rapid approaches
(
combined with novel hybridized nanomaterials for the sensitive
detection of POPs is currently a major challenge. Most recently,
the facile electrical detection of several target POPs through
Hence, a new strategy, i.e., SWCNTs decorated with mono-6-
deoxy-6-(p-aminophenylamino)-b-cyclodextrin (PCD) (Fig. 1),
has been applied to obtain novel hybridized chemosensors for
detection of POPs thanks to its special molecular structure, that
2
porous SnO nanostructures has been developed first by our
4
group; however, the sensitivity and selectivity need to be
improved.
is, a hydrophobic internal cavity and a hydrophilic external
25–30
surface for molecular recognition.
This route can greatly
As is well known, single-walled carbon nanotubes
improve sensitivity and selectivity for detecting organic mole-
31–36
(
SWCNTs) have been considered as chemical nanosensor
cules.
It can be expected that an inclusion complex with guest
5–12
materials for detecting analytes
due to their unique quasi-
molecules can be efficiently formed between PCD decorated
SWCNTs and POPs, such as TCB, CD-68, aldrin and HCB etc.
Therefore, synthesis of PCD and fabrication of PCD-decorated
SWCNTs (SWCNT–PCD) hybrid devices, which behave as
electrical sensors that are chemically specific and capable of
detecting nanomolar concentrations of TCB, are reported in the
present paper.
Research Center for Biomimetic Functional Materials and Sensing Devices
Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei,
Anhui, 230031, China. E-mail: jwang@iim.ac.cn; jhliu@iim.ac.cn;
xingjiuhuang@iim.ac.cn; Fax: +86-551-5592420
†
1
Electronic supplementary information (ESI) available. See DOI:
0.1039/c0jm04552g
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 11109–11115 | 11109

Fig. 1 Schematic representation of synthesis of PCD and preparation of SWCNT–PCD hybrids.
temperature, the precipitate could be removed by suction filtra-
ꢀ
2
. Experimental
tion and the filtrate was refrigerated for a couple of days at 4 C.
2
.1 Materials and chemicals
The white precipitate was recovered via suction filtration and
1
recrystallized twice to obtain a pure white solid. H NMR (400
b-cyclodextrin (b-CD) (95%) was purchased from Sinopharm
Chemical Reagent Co., Ltd., China. p-Phenylenediamine (98%),
p-toluenesulfonyl chloride (TsCl) (95%) and all other chemicals
ꢀ
MHz, (CD
3
)
2
SO, 25 C, TMS, d): 2.43 (s, 3 H), 3.20–3.40 (m,
overlaps with HOD), 3.44–3.66 (m, 28 H), 4.17–4.52 (m, 6 H),
4
.77 (s, 3 H), 4.84 (s, 4 H), 5.64–5.84 (m, 14 H), 7.43 (d, J ¼ 8.07
(
analytical pure grade) were obtained from Shanghai Chemical
Hz, 2 H), 7.75 (d, J ¼ 8.11 Hz, 2 H) ppm. Anal. calcd (%) for
C H O S$3H O: C, 43.81; H, 6.15; S, 2.39. Found (%): C,
Co. Ltd. China. The SWCNTs (CVD) used in this study were
purchased from Shenzhen Nanotech Port Co. Ltd. China. The
purity was declared to be above 95%.
4
9
76 37
2
4
3.58; H, 6.21; S, 2.28.
2.4 Preparation of mono-6-(p-aminophenylamino)-b-
cyclodextrin (PCD)
2
.2 Instruments
Fourier transform infrared (FT-IR) spectra were recorded on
b-CDtos (4.0 g) and p-phenylenediamine (0.8 g) were dissolved in
water (30 mL) containing triethylamine (20 mL), and the stirred
mixture was heated to reflux under a nitrogen atmosphere for 24
h. After evaporation under reduced pressure, the residue was
poured into vigorously stirred anhydrous ethanol (500 mL), and
the resultant mixture was stored in a refrigerator to produce
a slight red precipitate. The crude solid product was collected by
filtration and then purified by column chromatography on
a hydroxymethylcellulose column with an aqueous ammonium
bicarbonate eluent (0.05 M), followed by chromatography on
a Sephadex G-25 column with deionized water as the eluent, to
a Nexus-870 spectrophotometer. Nuclear magnetic resonance
ꢀ
(
NMR) spectra were acquired at 25 C using a Bruker Avance
spectrometer. Elemental analysis for C, H, and N was performed
using an Elementar Vario EL-III analyzer. Ultraviolet visible
near infrared (UV-Vis-NIR) absorption spectra were recorded
by using a Solidspec-3700 spectrophotometer. Field-emission
scanning electron microscopy (FESEM) images were taken by
a Sirion 200 field-emission scanning electron microscope. High
resolution transmission electron microscopy (HRTEM) images
were obtained from a JEOL JEM-2010 instrument operated at
1
00 kV. Thermogravimetric analysis (TGA) was performed using
1
give the product (2.2 g) in 50% yield. H NMR (400 MHz,
ꢀ
a Shimadzu TGA-50H analyzer in argon surroundings. Raman
spectra were collected from a DXR Smart Raman Spectrometer
using 25 mW of 514 nm radiation from a helium neon laser.
Integration times were provided as 30 s.
(
CD
3
)
2
SO, 25 C, TMS, d): 3.20–3.45 (m, overlaps with HOD),
3
.52–3.66 (m, 28 H), 4.20–4.63 (m, 6 H), 4.83–4.88 (s, 7 H), 5.57–
.95 (m, 14 H), 6.39 (d, J ¼ 8.48 Hz, 2 H), 6.43 (d, J ¼ 8.42 Hz, 2
34$7H O: C, 42.67; H,
.71; N, 2.07. Found (%): C, 42.36; H, 6.59; N, 2.23.
5
H) ppm. Anal. calcd (%) for C48
H
76
2
N O
2
6
2.3 Preparation of mono-6-deoxy-6-(p-toylsulfonyl)-b-
Cyclodextrin (b-CDtos)
2
.5 Purification and disentanglement of SWCNTs
b-CD (70 g) was suspended in water (500 mL), and 20 mL
aqueous solution including NaOH (6.6 g) was added dropwise to
the b-CD suspension so that the suspension gradually became
transparent. p-Toluenesulfonyl chloride (10 g) in acetonitrile
ꢀ
100 mg SWCNT raw soot was first heated in air at 350 C for 3 h.
The remaining soot was sonicated in 30 mL 37 wt% hydrochloric
acid for 4 h and then refluxed for 5 h. The solution was filtered
using a 0.20 mm Teflon filter under vacuum. The sediment was
washed with copious water, and then it was vacuum-dried at
(
30 mL) was added dropwise to the transparent solution so as to
form a white precipitate. After stirring for 2 h at ambient
1
1110 | J. Mater. Chem., 2011, 21, 11109–11115
This journal is ª The Royal Society of Chemistry 2011

ꢀ
6
0 C for one day. Disentanglement of the SWCNT bundles was
experiment was composed of 34 successive injections (8 mL per
injection). POP solutions were applied at a concentration
between 0.05 and 0.1 mM. In the microcalorimetric titration
experiments, each titration of PCD into the sample cell gave rise
to a heat of reaction, caused by the formation of inclusion
complexes between POP molecules and PCD. The heats of
reaction decrease after each injection of PCD because the
quantity of POP molecules available for forming inclusion
complexes is decreased. The dilution heat of titrant and analytes
has been measured and deducted in all ITC experiments.
performed by oleum. The obtained SWCNTs were soaked in
oleum (20% SO ) for 72 h using an immersion blender so that the
3
intercalation of acid into the tightly entangled network of
SWCNTs would loosen the ropes. After diluting with deionized
water, the mixture was centrifuged and the supernatant acid was
decanted off. The precipitate was washed with deionized water
three times and then ultrasonically dispersed into 20 mL 0.2%
benzalkonium chloride solution. The solution was centrifuged at
4
000 rpm for 20 mins. The supernatant solution was filtrated
with a 0.20 mm Teflon filter under vacuum, washed extensively
with deionized water until the pH of the filtrate reached 6 and
dried under vacuum. Finally, the purified SWCNTs were
3. Results and discussion
ꢀ
obtained by annealing in Ar at 900 C for 30 min to remove the
3
.1 Characterization of SWCNT–PCD hybrids
oxygen-based functional groups generated from the oleum
treatment. Approximate 25 mg of product was obtained.
PCD has been synthesized through a two-step reaction (Fig. 1),
i.e., preparation of mono-6-deoxy-6-(p-toylsulfonyl)-b-cyclo-
dextrin (b-CDtos) from b-cyclodextrin and p-toluenesulfonyl
chloride in aqueous solution including NaOH as the first step,
PCD was subsequently synthesized by the condensation of b-
CDtos with p-phenylenediamine in water in the presence of
triethylamine as a catalyst. The SWCNTs were functionalized
with PCD via the in situ generation of the corresponding aryl
diazonium of PCD. The CD (cyclodextrin) group is covalently
attached to the surface of the SWCNTs with the aid of a benzene
ring between the two moieties (Fig. 1). The structure, properties
and morphologies of the SWCNT–PCD hybrids can be
comprehensively analyzed by Raman spectroscopy, thermogra-
vimetric analysis (TGA), ultraviolet–visible–near infrared (UV-
Vis-NIR), field-emission scanning electron microscopy
2
.6 Preparation of SWCNT–PCD hybrids
In a typical experiment, 6 mg of the purified SWCNTs was
sonicated for 30 min in 10 mL of DMF. A solution of 100 mg
PCD (0.4 mmol) in 3 mL of DMF was added to the suspension.
After transferring to a septum-capped reaction flask and
bubbling with nitrogen for 10 min, 0.1 mL of isoamyl nitrite was
ꢀ
quickly added. The suspension was stirred in the dark at 70 C
for 24 h. After being cooled to room temperature, the suspension
was diluted with 30 mL DMF, filtered through a 0.2 mm Teflon
filter, and washed extensively with DMF until the filtrate became
ꢀ
colorless. Subsequently, it was dried in vacuum at 80 C for 24 h
to give a black powder of the modified SWCNTs (5 mg).
(
(
FESEM) and high resolution transmission electron microscopy
HRTEM).
2
.7 Preparation of electrode
The Raman spectra of the bare SWCNTs and SWCNT–PCD
The electrodes for the sensors were microfabricated on a silicon
substrate using standard lithographic patterning. A one micron
hybrids are shown in Fig. 2A. The degree of functionalization
37
can be preliminarily reflected in intensity of the D-band. After
functionalization with PCD, the relative intensities of three main
modes are changed. Compared to the tangential mode (G-band)
thick SiO
wafer to insulate the substrate using chemical vapor deposition
CVD). After photo lithographically defining the electrode area,
2
film was initially deposited on a (100) oriented silicon
(
ꢁ1
at ca. 1590 cm , the intensity of the radial breathing mode
a Cr adhesion layer and a ca. 300 nm-thick Au layer were
evaporated via e-beam. Finally, the electrodes were defined using
lift-off techniques.
ꢁ1
(
RBM) (ca. 160, 210, and 270 cm ) is slightly decreased;
however, the intensity of the disorder mode (D-band) at ca. 1290
ꢁ1
cm is significantly increased, and the D/G ratio value increases
from 0.08 (bare SWCNTs) to 0.2 (SWCNT–PCD). The increase
in the relative intensity of the D-band can be attributed to an
The obtained electrodes were cleaned for 45 min in hot
Piranha solution H O –H SO (3 : 1, v/v), rinsed copiously with
2
2
2
4
water, and dried under N2. Self-assembled monolayers of ami-
nopropyltriethoxy silane (APTES) were absorbed from 1%
solution in anhydrous toluene (AHT) for one hour at room
temperature, followed by rinsing and sonication with AHT and
3
increased number of sp -hybridized carbons in the nanotube
37
framework.
The removal of functional moieties from the pristine SWCNTs
in the inert environment by sufficient heating leads to mass loss in
the TGA measurements, which can be used to quantitatively
estimate the functionalization degree of the carbon nanotubes.
drying under N
2
.
2
.8 Microcalorimetric titration
ꢀ
When SWCNT–PCD hybrids are heated to 750 C in an argon
ꢁ1
ꢀ
The microcalorimetric titrations were performed at atmospheric
ꢀ
atmosphere (10 C min ), the total mass loss in the TGA
ꢀ
pressure and 25 C in H
2
O–MeOH (9 : 1, v/v) solution by using
experiment is ca. 36% (about 29% between 300–400 C); more-
Microcal VP-ITC titration microcalorimetry. All solutions were
degassed and thermostated using a thermostat accessory before
over, PCD has been efficiently functionalized on the SWCNTs
which is reflected in the higher decomposition temperature of the
SWCNT–PCD hybrids compared to that of PCD (Fig. 3). Again,
the Raman spectrum of SWCNT–PCD after the TGA experi-
ment (Fig. 2B) is found to be quite similar to that of pristine
SWCNTs, indicating that only intact nanotubes are left if the
functional moieties are removed.
the titration experiment. In each run, a H O–MeOH solution of
2
PCD host (2.00 mM) in a 0.30 mL syringe was sequentially
injected with stirring at 500 rpm into the calorimeter sample cell
2
containing a H O–MeOH solution of POP guests. The sample
cell volume was 1.430 mL in all experiments. Each titration
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 11109–11115 | 11111

Fig. 4 UV-Vis-NIR absorption spectra of bare SWCNTs and SWCNT–
PCD in DMF.
SWCNT–PCD suggests that metallic SWCNTs in the sample are
41
basically destroyed, which implies that metallic SWCNTs are
42
preferentially diazotized.
The bare and functionalized SWCNTs can be directly
observed using FESEM. As shown in Fig. 5A, most of the
SWCNTs are easily entangled so as to form large-sized nanotube
bundles. In contrast, PCD decorated SWCNTs can be effectively
exfoliated (Fig. 5B) and well dispersed in dimethylformamide
(
DMF), which may be related to the larger solubility of
SWCNT–PCD in DMF compared to bare SWCNTs. Moreover,
no precipitation or flocculation in the saturated solution of the
SWCNT–PCD hybrids can be observed over several months.
Besides, the HRTEM image of SWCNT-PCD (Fig. 5C) shows
the presence of individual SWCNTs with rugged surfaces, which
has been ascribed to the attachment of cyclodextrin functional
groups to the tube wall.
Fig. 2 Raman spectra (514 nm excitation) of SWCNTs, A) bare
ꢀ
SWCNTs and SWCNT–PCD. B) SWCNT–PCD after 750 C TGA
ꢀ
ꢁ1
treatment in an argon atmosphere at 10 C min . The insets show the
magnified RBM bands.
3
.2 Protocol and sensing behavior of SWCNT–PCD
hybridized devices
As shown in schematic graph (Fig. 6), an SWCNT–PCD film was
ꢁ1
spin-coated from 10 mg mL DMF solution onto a silicon
substrate with one micron thick SiO dielectric and interdigital
2
gold electrodes (300 nm thickness, 5 mm gap distance), which had
been previously self-assembled with a monolayer of amino-
propyltriethoxy silane (APTES). Aminosilanes are used because
43
they can enhance the absorption and localization of nanotubes.
Fig. 3 TGA of the purified SWCNTs, PCD and SWCNT–PCD hybrids
ꢀ
ꢁ1
in an argon atmosphere (10 C min ; incipient sample mass: 1.283, 2.277
and 1.402 mg for the purified SWCNTs, PCD and SWCNT–PCD
hybrids, respectively; crucible type: alumina, 150 mL).
The resistance of SWCNT–PCD devices range from 1 to 1.2 MU.
It is very important to control the quality of the dispersions so as
to ensure that the SWCNT–PCD hybrids form percolative
networks of largely individual tubes.
A cyclodextrin derivative was chosen to be attached to
SWCNTs due to its hydrophobic inner cavity and hydrophilic
outer surface, which acts as a good receptor for organic
substrates in aqueous solution. Herein, SWCNT–PCD hybrids
have been prepared and fabricated as sensing devices for the
detection of POPs (TCB, aldrin, mirex, HCB, and CD-68). These
molecules can be included inside the cavities of CD with different
binding affinities. The SWCNT–PCD sensing device was soaked
In addition to Raman and TGA, the functional degree of the
SWCNTs can also be evaluated by UV-Vis-NIR absorption
experiments. A high degree of covalent functionalization gives
rise to the disappearance of van Hove singularities of the
SWCNTs, which can be attributed to the disruption of the
2
38
delocalized p-conjugation in the sp -hybridized nanotubes.
However, the specific van Hove singularities in the present
SWCNT-PCD hybrids are partially retained (Fig. 4), indicating
that the p-conjugated electron structures of the SWCNTs are not
in H O–MeOH (9 : 1, v/v) solutions of POPs for 1 h, and the
2
POPs molecules enter the cavities of CD (Fig. 6), they were
39,40
severely damaged.
In addition, the disappearance of the band
2
afterwards washed with H O, and finally dried in a vacuum oven
ꢀ
at ca. 550 nm in the UV-Vis-NIR absorption spectrum of
(60 C) for 30 min to remove residual solvent.
1
1112 | J. Mater. Chem., 2011, 21, 11109–11115
This journal is ª The Royal Society of Chemistry 2011

Fig. 5 (A) FESEM image of bare SWCNTs showing the bundles of nanotubes. (B) FESEM image of SWCNT–PCD showing exfoliation of nanotubes.
(C) HRTEM image of SWCNT–PCD. The inset is a TEM image of individual pristine SWCNTs.
3
.3 Sensing mechanism of SWCNT–PCD hybrids for detecting
POPs
The number of captured POP molecules directly depends on their
binding abilities towards the CD cavities. In order to make
a quantitative assessment of the inclusion complexation behavior
of the PCD with these POP molecules, microcalorimetric titra-
tion experiments were performed using Microcal VP-ITC titra-
tion microcalorimetry, which allowed us to determine
ꢀ
simultaneously the standard enthalpy changes (DH ), entropy
ꢀ
changes (DS ) and equilibrium constant (K) (Table S1 in the
ESI†). Typical titration curves of host PCD with guest TCB are
shown in Fig. 9.
Fig. 6 Schematic view of sensor structure and its interaction with POPs.
ꢀ
The values of K, Gibbs free energy change (DG )
ꢀ
ꢀ
ꢀ
(
DG ¼ ꢁRTlnK ¼ DH – TDS , where R is the gas constant,
Attention now turns to the study of the electrical behavior of
SWCNT–PCD sensing devices for POPs. The current–voltage
(
I–V) curves were measured via a picoammeter voltage source-
meter (Keithley 6487, USA) with a bias voltage from ꢁ2 to +2 V
between the two electrodes at room temperature. The typical I–V
curves of hybrid SWCNT–PCD devices before and after binding
TCB and CD-68 are displayed in Fig. 7. It has been found that
after binding with the POP molecules the conductance of the
SWCNT–PCD hybrid networks decreases; however, in the
2
control tests, only H O–MeOH solution without POPs and bare
SWCNTs were used instead of SWCNT–PCD (data not shown),
and the conductance hardly changed. This suggests that the POP
molecules captured in the cavities will cause a rearrangement in
the charge distribution of the CD moieties in the SWCNT–PCD
hybrids, and induce charge transfer from the CD molecules to the
SWCNTs, which leads to the decrease in charge carrier density in
the p-type semiconducting SWCNTs. On the other hand, the
POP molecules captured in the CD cavities can engender
a further decrease of the charge mobility in SWCNTs either by
altering the scattering potentials of the CD molecules or by
44,45
causing further deformation of the SWCNTs.
In addition,
by binding different POPs at the same concentration, 500 nM,
different conductance change ratios (CCRs) of the SWCNT–
PCD hybrid networks can be obtained; ca. 1.6% for HCB, ca.
3
.3% for mirex, ca. 3.8% for CD-68, ca. 5.6% for aldrin, and ca.
2.5% for TCB.
1
Further, the detection of TCB was performed at different
concentrations. As shown in Fig. 8, the CCR of SWCNT–PCD
hybrid networks obtained is ca. 1.7% even at 25 nM, suggesting
that the sensing can be qualified as having a nanomolar level of
sensitivity.
Fig. 7 The current–voltage (I–V) curves of the SWCNT–PCD sensing
devices before and after binding of the POP molecules at concentrations
of 500 nM (A for TCB, B for CD-68).
This journal is ª The Royal Society of Chemistry 2011
J. Mater. Chem., 2011, 21, 11109–11115 | 11113

Table 1 Values of the CCR (conductance change ratio) of SWCNT–
PCD devices before and after binding of POPs, to reflect their sensing
ꢀ
towards different POP molecules the K and ꢁDG when PCD forms
complexes with these POP molecules can be compared
ꢁ
1
ꢀ
ꢁ1
POPs
CCR/%
K/M
ꢁDG /kJ mol
TCB
12.5
5.6
3.8
3.3
1.6
9145 ꢂ 229
3613 ꢂ 42
2667 ꢂ 82
1968 ꢂ 15
823 ꢂ 36
22.59 ꢂ 0.07
20.3 ꢂ 0.03
19.55 ꢂ 0.08
18.8 ꢂ 0.03
16.63 ꢂ 0.1
Aldrin
CD-68
Mirex
HCB
molecules included in the host cavities, suggesting that the
SWCNT–PCD hybrid devices can be used for selective sensing
recognition of POPs.
Fig. 8 CCR (conductance change ratio) of the SWCNT–PCD sensing
devices in response to TCB in different concentration solution.
T ¼ 298.15 K) obtained for the complexation of PCD with POPs,
and the CCR of the SWCNT–PCD devices before and after
binding of these POPs are listed in Table 1. The K values for the
complexation of PCD with these POPs exhibit the following
sequence of binding abilities: TCB > aldrin > CD-68 > mirex >
HCB; moreover, the K values correlate with the magnitudes of
the CCRs of the SWCNT–PCD devices before and after binding
of these POP molecules. After plotting the complex formation
constants versus the values of the CCR of the SWCNT–PCD
devices, a good linear relationship with a correlation coefficient
of 0.997 can be found. The variance of change in the CCR of the
SWCNT–PCD devices depends on the quantities of guest
4
. Conclusions
In summary, novel SWCNT–PCD hybrids have been success-
fully synthesized through an in situ diazonium reaction between
SWCNTs and PCD. The results reveal that the one-dimensional
electronic structures of the functionalized tubes could basically
be maintained without damaging their electronic properties. In
comparison with our recent results, the fabricated electrical
sensor based on SWCNT–PCD hybrids has been successfully
used to detect POPs, and it displays excellent sensitivity and
selectivity due to the concept of molecular recognition. The K
values for the complexation of the PCD with the different POPs
correlate with the magnitudes of the CCRs of the SWCNT–PCD
device after binding with these POP molecules. Another impor-
tant advantage is that the present sensing device overcomes the
limitation of some chemical signal-based methods caused by the
inactivity of POPs. It is reasonable to believe that the hybridized
SWCNT–PCD sensor holds great potential to be developed as
a real time environmental monitor.
Acknowledgements
This work is supported by the One Hundred Person Project of
the Chinese Academy of Sciences (CAS), China, the National
Basic Research Program of China (Grant No. 2007CB936603),
The National Key Scientific Program-Nanoscience and Nano-
technology (Grant No. 2011CB933700), and the National
Natural Science Foundation of China (Grant Nos. 20875004,
2
1075002 and 61071054). Dr Jin Wang thanks the National
Natural Science Foundation of China (Grant No. 21077106) and
Innovation Project of Chinese Academy of Sciences (KCX2-
YW-G-058) for financial support.
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