hexa”uorobisphenol a covalently functionalized single...

Delivered by Ingenta toUniversity of PatrasIP 150140184110

Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE

Copyright copy 2011 American Scientific Publishers

All rights reserved

Printed in the United States of America

Journal ofNanoscience and Nanotechnology

Vol 11 4874ndash4881 2011

Hexafluorobisphenol A Covalently Functionalized

Single-Walled Carbon Nanotubes for Detection of

Dimethyl Methylphosphonate Vapor

Yanyan Wang Zi Wang Nantao Hulowast Liangming Wei Dong XuHao Wei Eric Siu-Wai Kong and Yafei Zhanglowast

National Key Laboratory of NanoMicro Fabrication Technology Key Laboratory for Thin Film and Microfabrication of the Ministry of

Education Research Institute of MicroNano Science and Technology Shanghai Jiao Tong University Shanghai 200240 P R China

Hexafluorobisphenol A (6FBPA) as a novel nerve agents sensing molecule has been success-fully attached onto the surface of single-walled carbon nanotubes (SWNTs) The sensing groupshave been confirmed by infrared spectroscopy Raman spectroscopy and X-ray photoelectron spec-trometry The results revealed that the sensing groups had been successfully anchored on thesurface of nanotubes The quantitative determination of the functional groups has also been carriedout through characterization by thermogravimetric analysis Furthermore the morphology of theresultant SWNT-6FBPA hybrids has been observed by transmission electron microscopy and scan-ning electron microscopy Due to the existence of phenolic hydroxyl groups which can form stronghydrogen-bonding with dimethyl methylphosphonate (DMMP) (simulant of nerve agent sarin) thefunctionalized SWNTs showed excellent sensitivity and selectivity while the sensing devices havebeen fabricated

Keywords Hexafluorobisphenol A Covalent Functionalization Single-Walled CarbonNanotubes Gas Sensor

1 INTRODUCTION

In order to satisfy the requirement of defending home-

land security and monitoring application of agriculture

medical and manufacturing environments itrsquos neces-

sary for us to fabricate novel sensing devices with

low power low cost as well as portable properties1ndash9

Many kinds of sensing devices including electrochemical

sensors1011 chemoreceptive sensors12 microcantilever-

based sensors1314 and quartz-crystal microbalance

sensors1516 have been reported focused on this field

Therein chemiresistive sensors such as semi-conducting

metal oxide sensors17 organic semiconductors sensors18

and carbon nanotubes sensors19 etc exhibit great chal-

lenges for gas sensing due to their low power con-

sumption and the ease of high precision resistance

measurements Especially single-walled carbon nanotubes

(SWNTs) which can be considered as leading candidate

materials for chemiresistive sensors show high sensitiv-

ity and fast response for analytes on account of their

high aspect ratio large specific surface area excellent

lowastAuthors to whom correspondence should be addressed

chemical stability and unique quasi-one-dimensional elec-

tronic structures20ndash23

As excellent sensing materials semi-conducting pris-

tine SWNTs have been utilized for detecting some small

gas molecules eg ammonia ethanol vapor NO2 CO

CH4 chemical warfare agents (CWAs)24ndash29 and among

others Further enhancements of the sensing performance

of SWNTs have been achieved through chemical function-

alization methods which can also greatly benefit both of

the processibility and dispersion of SWNTs30ndash32 Several

sensing materials such as conducting polymer33 metals34

and metal oxide35 etc have been chemically attached onto

the surface of SWNTs and played important roles in gas

detection

As a prominent sensing material hexafluoroisopropanol

(HFIP) substituents have recently aroused much inter-

est owing to the formation of strong hydrogen-bonding

between HFIP groups and sensing agents36 This charac-

teristic makes sense especially for the detection of explo-

sives and CWAs Based on the strong hydrogen-bonding a

series of HFIP derivatives have been coupled with SWNTs

and the resultant hybrids can serve as excellent sensitive

sensors for explosives CWAs and relative compounds3738

4874 J Nanosci Nanotechnol 2011 Vol 11 No 6 1533-48802011114874008 doi101166jnn20114193


Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE

Wang et al Hexafluorobisphenol A Covalently Functionalized Single-Walled Carbon Nanotubes for Detection of DMMP Vapor

Fig 1 Schematic view of the SWNT-6FBPA hybrids and their specific

interactions with DMMP via hydrogen-bonding

Hexafluorobisphenol A (6FBPA) another similar nerve

agents sensing material have been used for chemical

vapor sensing through attaching to the side chain or main

chain of polymers363940 Since the electron-withdrawing

effect of fluorine atoms existed in 6FBPA can maximize

the hydrogen-bond acidity of hydroxyl groups ie the

hydrogen-bond basicity of hydroxylic oxygen atoms can

be minimised itrsquos considered as a promising candidate

for gas sensing material by hydrogen-bonding interac-

tion And itrsquos a great challenge to combine this sensing

material with SWNTs for explosive CWAs and relative

compounds sensing especially for dimethyl methylphos-

phonate (DMMP) through the hydrogen-bonding interac-

tion (shown in Fig 1)

Therefore in the present study 6FBPA has been firstly

attached onto the surface of SWNTs Due to the strong

hydrogen-bonding interaction between 6FBPA sensing

groups and DMMP the resultant chemical sensor exhib-

ited higher sensitivity and selectivity compared with the

bare SWNTs based sensors The achievement of SWNT-

6FBPA hybrids sensing materials with high performance

is expected to pave a new avenue toward the realization of

low cost low power and portable sensing device system

2 EXPERIMENTAL DETAILS

21 Materials

The 6FBPA (98) was obtained from Alfa-Aesar and used

as received DMMP (97) was obtained from Sigma-

Aldrich All of other chemicals (analytical reagent grade)

were purchased from Shanghai Chemical Reagents Co

Ltd (China) SWNTs used in this study were synthesized

by the arc discharge method All of organic solvents were

purified by distillation

22 Purification of SWNTs

The purification of SWNTs was executed by air oxidation

at 365 C for 30 min followed by refluxing with a 31

mixture of concentrated sulfuric acid and nitric acid at

80 C for 30 min As a result of the purification process

carboxylic groups are associated with the defect sites and

the terminated carbons in chemically shortened nanotubes

The purified SWNTs contain sim4 carboxylic acid groups

as estimated by acid-base titration4142 The final purified

SWNTs have a purity of about 95

23 Preparation of SWNT-6FBPA Hybrids Material

The procedure for the preparation of SWNT-6FBPA

hybrids is based on the methodology already demonstrated

by several authors4344 The typical approach was as fol-

lows (Fig 2) 300 mg purified SWNTs were suspended in

40 mL thionyl chloride (SOCl2) and 1 mL dimethyl for-

mamide (DMF) These suspensions were refluxed at 65 Cwhile keeping stirring for 24 h The black solid was then

separated by filtration and washed with anhydrous tetrahy-

drofuran (THF) several times Subsequently it was vac-

uum dried at room temperature for 1 h As a result the

acylated SWNTs were obtained 100 mg of SWNTs with

acyl chloride groups were mixed with 200 mg of 6FBPA in

DMF which was freshly distilled at reduced pressure The

mixture was ultrasonicated for several minutes and 1 mL

of pyridine was added the reaction was allowed to take

place by keeping stirring for 24 h at room temperature

The resultant suspension was separated by filtration with

the same 022 PTFE membrane filter Followed by thor-

oughly washing with DMF and alcohol and finally dried

overnight in the vacuum oven at 60 C

24 Fabrication of SWNT-6FBPA HybridizedSensing Devices

The standard microfabrication procedures were carried out

to obtain the electrodes for the sensors array here The

interdigitated electrode fingers were made by sputtering

10 nm Cr and 180 nm Au onto a patterned photoresist

mold A lift-off process was further introduced to remove

the photoresist The resultant electrodes were sonicated

in ethanol washed with deionized water thoroughly and

finally dried by nitrogen flow

In order to fabricate the SWNT-6FBPA hybrids sens-

ing devices the typical protocols have been designed as

follows the as-prepared SWNT-6FBPA hybrids were sus-

pended in DMF (01 g mLminus1) and ultrasonicated for 2 h

in order to make sure the hybrids had been efficiently dis-

persed in DMF Subsequently 01 L of the above solution

was extracted and deposited onto the electrode gap using

a microsyringe After evaporation of the solution through

putting the devices in the vacuum oven at 60 C for 1 h a

network of SWNT-6FBPA hybrids bridged each electrode

gap could be formed Further thermal treatment at 150 Cin the vacuum oven for 1 h was executed in order to opti-

mize the contact between SWNTs and the gold electrodes

J Nanosci Nanotechnol 11 4874ndash4881 2011 4875


Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE

Hexafluorobisphenol A Covalently Functionalized Single-Walled Carbon Nanotubes for Detection of DMMP Vapor Wang et al

Fig 2 Outline for the preparation of SWNT-6FBPA hybrids

25 Characterization

Fourier transform infrared (FTIR) spectra were recorded

on a Bruker (Germany) VERTEX 70 spectrometer over

a range from 400 to 4000 cmminus1 with DTGS or MCT

as detector Raman scattering was performed on a Ren-

ishaw inVia Reflex Raman spectrometer using a 514-nm

laser source X-ray photoelectron spectrometry (XPS) was

carried out on a Kratos Axis Ultra DLD using monochro-

mated Al K X-ray beams as the excitation source Bind-

ing energies were calibrated relative to the C 1s peak at

2846 eV The thermogravimetric analysis (TGA) was per-

formed under an argon atmosphere using a heating rate

of 10 Cmin started from 50 C up to 850 C The mor-

phologies of the SWNTs were observed by field emis-

sion scanning electron microscopy (FE-SEM Carl Zeiss

Ultra 55) Transmission electron microscopy (TEM) was

obtained on JEM-2100 (Japan) and the accelerating volt-

age was 200 kV

3 RESULTS AND DISCUSSION

31 Synthesis and Characterization ofSWNT-6FBPA Hybrids

The hybrids were obtained via the reaction between acy-

lated SWNTs and 6FBPA through formation of ester

bonds In order to make sure there were plenty of free

hydroxyl groups on the surface of SWNTs the amount

of 6FBPA needed to be much larger than that of the acyl

groups on the surface of SWNTs

FTIR was utilized to confirm the obtained SWNT-

6FBPA hybrids Figure 3(a) illustrates the typical spec-

tra of the acidized SWNTs As shown in Figure 3(a) a

weak peak appeared at 1722 cmminus1 which was attributed

to the C O stretching vibration band of the carboxylic

acid groups As to the SWNTs modified with 6FBPA

(Fig 3(b)) the peak of carboxylic acid located at

1722 cmminus1 was disappeared after treated with 6FBPA and

a new strong band at 1633 cmminus1 attributed to the vibration

of ester group appeared In addition another strong peak

located at 3435 cmminus1 was attributed to hydroxyl groups of

6FBPA which suggested 6FBPA was successfully attached

onto the SWNTs

The covalent attachment can be also confirmed by

Raman spectra (Figs 4(a and b)) All spectra of SWNTs

with different treatments contained characteristic peaks at

1588 cmminus1 (tangential mode) and at 1344 cmminus1 (disor-

der mode) As the disorder mode is the diagnostic of

disruptions in the hexagonal framework of the SWNTs

the fact that the relative intensity of this mode (R =IDIG) increased provided direct evidence for the covalent

modification of SWNTs45 Moreover the multiple peaks

observed in the radial breathing mode (RBM) of SWNTs

(ca 163 cmminus1) could be ascribable to distribution of diam-

eters in the SWNTs samples37 As shown in Figure 4(c)

two bands for the RBM of as-purified SWNTs can be

observed at 149 cmminus1 and 163 cmminus1 respectively which

can be concluded that most of the SWNTs we used belong

to the semi-conducting SWNTs46

Degree of functionalisation of SWNTs can be estimated

quantitatively by TGA through measurement of mass loss

that accompanies removal of functional moieties from the

SWNTs in an inert environment with sufficient heating

As shown in Figure 5 when SWNT-6FBPA hybrids are

heated to 850 C in an argon atmosphere ca 32 mass

loss in the TGA experiment can be observed Without con-

sideration of the weight loss of intrinsic SWNTs during

heat treatment the molar ratio of the 6FBPA to C atoms

can be calculated to be 191 ie ca 1 6FBPA sensing

group can be anchored onto the surface of SWNTs in every

91 carbon atoms which is in agreement with the amount

of carboxylic acid groups estimated by acid-base titration

In order to detect the elements of the functional groups

attached on the surface of SWNTs further characterization

Fig 3 FT-IR spectra of SWNTs with different treatments (a) acidized

SWNTs and (b) 6FBPA modified SWNTs

4876 J Nanosci Nanotechnol 11 4874ndash4881 2011


Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)

Fig 4 Raman spectra (514 nm excitation) of SWNTs (a) purified

SWNTs (b) SWNT-6FBPA hybrids and (c) expanded view of the RBM

of bare SWNTs

performed by XPS has also been carried out As shown

in Figure 6 F 1s peak at a binding energy of 6885 eV

which was attributed to the ndashCF3 groups appeared As

expected the appearance of such a peak further suggests

the successful attachment of 6FBPA onto the surface

of SWNTs Furthermore elemental composition analysis

shows the presence of atomic percent of C F O atoms

as 8845 510 and 645 respectively The atomic

ratio of carbon to fluorine can be calculated to be 1731

Fig 5 TGA curve of SWNT-6FBPA hybrids in an argon atmosphere

according to the ratio of the percentage of C atoms with

that of F atoms ie 104 C atoms per 6FBPA sensing

group can be estimated since there are 6 F atoms in the

molecule of 6FBPA Excluding 15 C atoms in 6FBPA

sensing groups 1 in 89 C atoms of SWNTs can be

anchored by one 6FBPA sensing group which agrees very

well with the data resulted from the TGA analysis

The SWNT-6FBPA hybrids displayed an excellent sol-

ubility in various organic solvents eg DMF N N -

dimethylacetamide (DMAc) alcohol etc As shown in

Figure 7 the hybrids dispersed in the organic solvents

very well No precipitation can be observed in a couple of

months which suggested that 6FBPA groups on the sur-

face of SWNTs greatly enhanced the solubility of SWNTs

As TEM provides sufficient resolution that it can be

used to obtain some direct visualization of the length or

diameter distribution and the defects itrsquos necessary to clar-

ify the morphology of SWNTs by TEM As shown in

Figure 8 the SWNTs with specific rugged surface can be

observed which could be attributed to the covalent attach-

ment of 6FBPA on the wall of SWNTs Meanwhile the

layer structure of SWNTs was still remained which sug-

gested that the covalent modification didnrsquot destroy the

tube structure

32 Evaluation of Sensing Device Based onSWNT-6FBPA Hybrids

For the purpose of depositing SWNTs-6FBPA hybrids on

the electrode the electrode gap needs to be suitably con-

trolled Therefore the gap distance between electrodes was

fixed at 10 m here (as shown in Fig 9(a)) in order

to make sure the network structure of SWNTs-6FBPA

hybrids can be totally formed

After the electrode was fabricated the hybrids solution

was dip-dropped between the electrodes followed by ther-

mal treatments to remove the solvents and consequently



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)

Fig 6 XPS analysis of SWNT-6FBPA hybrids (a) C1s (b) F1s and

(c) O1s

the SWNT-6FBPA network formed The density of SWNT-

6FBPA was very important and needed to be carefully con-

trolled through adjusting both of the concentration of the

SWNTs in the solvents and the drop volume of the solu-

tion Hence a 01 L drop of SWNT-6FBPA in DMF (the

concentration was fixed at 01 gmLminus1) was used here to

dip between the electrodes and dried to form the network

of SWNTs Figure 9(b) shows the SEM image of a net-

work of SWNT-6FBPA between Au electrodes Fine web

Fig 7 Photograph of SWNT-6FBPA hybrids in (a) DMF (b) DMAc

(c) alcohol

structure of SWNTs can be observed and consequently the

circuit can be formed when the voltage is applied The

contact resistance was measured to be about 1500 when

the 100 mV of voltage was applied

In order to detect the response of the hybrid sensors to

different concentrations of DMMP a homemade gas han-

dling system which is illustrated in our previous study4

has been used Nitrogen as both of the carrier and diluting

gas was used to bubble DMMP liquid through a porous

glass-disc bubbler and consequently DMMP vapor can be

formed The concentration of DMMP vapor can be eas-

ily controlled by dilution with nitrogen using a mass flow

controller

After the hybrids sensor was fabricated the sensor

responses to different concentrations of DMMP vapor

were measured at room temperature Nitrogen was used as

a balance gas at a flow rate of 1 Lminminus1 The humidity

Fig 8 TEM image of SWNT-6FBPA hybrids



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


Fig 9 SEM images of (a) sensor electrode array and (b) network of

SWNT-6FBPA hybrids bridged electrode

inside the test chamber was monitored by a Honeywell

HIH-4000 humidity sensor (Honeywell Inc) and is less

than 20 The variation of the resistance of the hybrids

sensor was detected by applying a low sampling volt-

age of 100 mV between the two electrodes The sensor

response (Rr) upon exposure to DMMP vapor is defined

by the following equation Rr= 100timesR1minusR0R0 =100timesRR0 where R0 is the resistance of SWNT-6FBPA

hybrids network before the exposure to DMMP vapors and

R1 is the resistance in the DMMPN2 mixed gas

Figures 10(a and b) show responses of the hybrids

sensor to DMMP vapor under the concentration of 05ndash

20 ppm It is obviously seen that the hybrids sensors show

a fast and highly reversible resistance response to differ-

ent concentrations of DMMP vapors When the DMMP

vapor was introduced into the test cell the resistance of

the sensor increased significantly over a period of 16 min

We define this period time as the effective response time

in order to evaluate the performance of the sensor which

has been illustrated in our paper reported before4 The

resistance change of the sensor increases with the increase

of the DMMP concentration As the sensor exposed to

DMMP vapor with the concentration at 20 ppm ca

510 resistance change could be achieved Actually the

(a)

(b)

Fig 10 (a) The response curve of the hybrid sensor to DMMP vapor

under the concentrations of 05ndash20 ppm and (b) The relationship of the

response of the sensors with the concentrations of DMMP

variation of the resistance response of the sensor to the

DMMP can be observed obviously at the whole concen-

tration of DMMP between 05 ppm and 20 ppm Even

the concentration of DMMP is as low as 05 ppm ca

221 variation in the resistance can be still observed

clearly On account of the limiting capability of the gas

mixing apparatus a lower concentration cannot precisely

be defined in our experiment Most importantly the sensor

response is recoverable with the decrease of the resis-

tance as well as the essential recovery of the curve to the

initial value when the test cell was illuminated with IR

lamp and flushed with N2 over a period of 12 min Fur-

thermore the relationship of the response of the sensors

with the concentration of DMMP can be also judged from

Figure 10(b) When the concentration of DMMP is very

low the response of the sensors can be increased obviously

as the concentration of the DMMP increases however fur-

ther increase of the concentration of analytes results in

less variation of the response curve especially for the high

concentration of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


Since the reproducibility and selectivity are two key fac-

tors for the evaluation of a gas sensor itrsquos essential to

study the reproducibility and selectivity properties of the

obtained hybrids sensor The reproducibility of the sen-

sor has been investigated through exposure of the hybrids

sensor to 10 ppm DMMP vapor repeatedly As shown in

Figure 11(a) six cycles of exposure to DMMP vapors

has been executed It shows that both of the resistance

response levels and recovery abilities for the hybrids sen-

sor are maintained after several cycles which indicates that

the hybrids sensor has a high reproducibility characteris-

tic Furthermore the selectivity of the hybrids sensor has

also been studied by using different analytes eg DMMP

hexane chloroform water xylene dichloromethane and

methanol The saturated concentration of vapors were pro-

duced at room temperature and diluted with N2 to 1

concentrations As shown in Figure 11(b) more than six

times magnitude of response to DMMP vapors for the

hybrid sensor can be observed in comparison with other

analytes which is very fascinating as we can note that

(a)

(b)

Fig 11 (a) Reproducibility of the response of SWNT-6FBPA hybrid

sensors to 10 ppm DMMP vapor and (b) response of the hybrid sensors

to DMMP compared with other analytes diluted to 1 of saturated vapor

concentrations

the equilibrium vapor pressure of methanol (167 000 ppm)

is more than 100 times larger in contrast with DMMP

(1600 ppm) The result suggests that the SWNT-6FBPA

hybrid sensors exhibit a high selectivity and can be consid-

ered as an excellent candidate for the detection of DMMP

In order to investigate the effects of the decoration

of 6FBPA on the sensitivity and selectivity of SWNTs

bare SWNT sensor has been fabricated through deposi-

tion of SWNTs on Au electrodes and the comparison has

been made between bare SWNT sensor and SWNT-6FBPA

hybrid sensor Figure 12 shows resistance responses of

the two sensors to different DMMP concentrations It is

obvious that the SWNT-6FBPA hybrid sensor has a higher

resistance response than that of bare SWNT sensor for

each DMMP concentration At 20 ppm concentration of

DMMP the response of SWNT-6FBPA hybrid sensor to

DMMP is ca 36 times larger than that of bare SWNT

sensor When the DMMP concentration is decreased to

1 ppm the response of SWNT-6FBPA hybrid sensor is

more than ten times higher than that of bare SWNT sensor

The attachment of 6FBPA sensing groups onto the surface

of SWNTs can result in remarkably increase of both of the

sensitivity and selectivity for detecting DMMP vapor This

maybe due to the fact that the strong hydrogen-bonding

interaction between 6FBPA groups and DMMP can effi-

ciently improve the sensitivity for detecting DMMP which

has been widely reported by many researchers3336ndash40 As

we know DMMP is a kind of electron donating molecule4

when it gets close to the hybrids it can interact with

SWNTs directly Consequently the direct charge transfer

between the SWNTs and DMMP takes place which makes

a reduction of the density of the holes in SWNTs and

causes an increase in their electrical resistance47 During

Fig 12 The comparison results of the resistant changes between

SWNT-6FBPA hybrid sensor and bare SWNT sensor at different concen-

trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


this process the presence of the 6FBPA sensing groups on

the surface of SWNTs is intended to enhance the sensing

capability of SWNTs through promoting the interaction

between the DMMP and 6FBPA sensing groups by the

formation of the hydrogen bond (OndashH O= P) (Fig 1)

4 CONCLUSIONS

A novel sensing material 6FBPA has been success-

fully anchored onto the surface of SWNTs The acyl

groups associated with SWNTs participated in the reaction

through formation of ester bonds This process enabled

efficient dispersion of SWNTs in several organic solvents

The obtained hybrids suspension can be easily drop-cast

between the electrode gaps and as a result a network of

SWNTs with sensing groups was formed The resultant

chemical sensor exhibited higher sensitivity and selectivity

compared with the bare SWNTs based sensors

Acknowledgments The authors gratefully acknowl-

edge financial support by National Basic Research

Program of China no 2006CB300406 National Nat-

ural Science Foundation of China nos 50730008

30772434 and 61006002 Shanghai Science and Tech-

nology Grant nos 1052nm02000 and 1052nm06800

Shanghai-Applied Materials Research and Development

Fund no 09520714400

References and Notes

1 D R Kauffman and A Star Chem Soc Rev 37 1197 (2008)2 E S Snow F K Perkins and J A Robinson Chem Soc Rev

35 790 (2006)3 S V Patel T E Mlsna B Fruhberger E Klaassen S Cemalovic

and D R Baselt Sens Actuators B 96 541 (2003)4 Y Y Wang Z H Zhou Z Yang X H Chen D Xu and Y F

Zhang Nanotechnology 20 345502 (2009)5 C Zuniga M Rinaldi S M Khamis A T Johnson and G Piazza

Appl Phys Lett 94 223122 (2009)6 D R Kauffman and A Star Angew Chem Int Ed 47 6550 (2008)7 D Du M Wang J Cai Y Tao H Tua and A Zhang Analyst

133 1790 (2008)8 P Vichchulada Q H Zhang and M D Lay Analyst 132 719

(2007)9 J Yan H J Zhou P Yu L Su and L Q Mao Adv Mater 20 2899

(2008)10 G L Liu and Y H Lin Anal Chem 77 5894 (2005)11 J W Grate S N Kaganove S J Patrash R Craig and M Bliss

Chem Mater 9 1201 (1997)12 S M Kanan A Waghe B L Jensen and C P Tripp Talanta

72 401 (2007)13 I Voiculescu M E Zaghloul R A Mcgill E J Houser and G K

Fedder IEEE Sens J 5 641 (2005)14 C Karnati H W Du H F Ji X H Xu Y Lvov A Mulchandani

P Mulchandani and W Chen Biosens Bioelectron 22 2636 (2007)

15 W P Carey and B R Kowalski Anal Chem 58 3077 (1986)16 O S Milanko S A Milinkovic and L V Rajakovic Anal Chim

Acta 269 289 (1992)17 A Kolmakov and M Moskovits Annu Rev Mater Res 34 151

(2004)18 R A Potyrailo Angew Chem Int Ed 45 702 (2006)19 E S Snow F K Perkins E J Houser S C Badescu and T L

Reinecke Science 307 1942 (2005)20 F Kreupl A P Graham G S Duesberg W Steinhoumlgl M Liebau

E Unger and W Houmlnlein Microelectron Eng 64 399 (2002)21 C Cantalini L Valentini I Armentano J M Kenny L Lozzi and

S Santucci J Eur Ceram Soc 24 1405 (2004)22 J Suehiro G B Zhou H Imakiire W D Ding and M Hara Sens

Actuators B 108 398 (2005)23 R H Baughman A A Zakhidov and W A Heer Science 297 787

(2002)24 A Star V Joshi S Skarupo D Thomas and J C P Gabriel

J Phys Chem B 110 21014 (2006)25 Q Zhao Z H Gan and Q K Zhuang Electroanalysis 14 1609

(2002)26 W S Cho S I Moon Y D Lee Y H Lee J H Park and B K

Ju IEEE Electron Device Lett 26 498 (2005)27 H Chang J D Lee S M Lee and Y H Lee Appl Phys Lett

79 3863 (2001)28 L M Dai P Soundarrajan and T Kim Pure Appl Chem 74 1753

(2002)29 J J Zhao A Buldum J Han and J P Lu Nanotechnology 13 195

(2002)30 J Kong M G Chapline and H J Dai Adv Mater 13 1384 (2001)31 K H An S Y Jeong H R Hwang and Y H Lee Adv Mater

16 1005 (2004)32 E Bekyarova M Davis T Burch M E Itkis B Zhao S Sunshine

and R C Haddon J Phys Chem B 108 19717 (2004)33 F Wang H W Gu and T M Swager J Am Chem Soc 130 5392

(2008)34 W Q Han and A Zettl Nano Lett 3 681 (2003)35 E S Forzani X L Li P M Zhang N J Tao R Zhang I Amlani

R Tsui and L A Nagahara Small 2 1283 (2006)36 J W Grate Chem Rev 108 726 (2008)37 L T Kong J Wang X C Fu Y Zhong F L Meng T Luo and

J H Liu Carbon 48 1262 (2010)38 L T Kong J Wang T Luo F L Meng X Chen M Q Li and

J H Liu Analyst 135 368 (2010)39 J W Grate S N Kaganove and D A Nelson Chem Innovations

30 29 (2000)40 J W Grate S J Patrash S N Kaganove M H Abraham B M

Wise and N B Gallagher Anal Chem 73 5247 (2001)41 N T Hu H W Zhou G D Dang X H Rao C H Chen and

W J Zhang Polym Int 56 655 (2007)42 H Hu P Bhowmik B Zhao M A Hamon M E Itkis and R C

Haddon Chem Phys Lett 345 25 (2001)43 J Chen A M Rao S Lyuksyutov M E Itkis M A Hamon

H Hu R W Cohn P C Eklund D T Colbert R E Smalley and

R C Haddon J Phys Chem B 105 2525 (2001)44 N T Hu G D Dang H W Zhou J Jing and C H Chen Mater

Lett 61 5285 (2007)45 C A Dyke and J M Tour J Phys Chem A 108 11151 (2004)46 R Krupke F Hennrich H V Loumlhneysen and M M Kappes

Science 301 344 (2003)47 J P Novak E S Snow E J Houser D Park J L Stepnowski

and R A McGill Appl Phys Lett 83 4026 (2003)

Received 27 September 2010 Accepted 26 November 2010



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


Fig 1 Schematic view of the SWNT-6FBPA hybrids and their specific

interactions with DMMP via hydrogen-bonding

Hexafluorobisphenol A (6FBPA) another similar nerve

agents sensing material have been used for chemical

vapor sensing through attaching to the side chain or main

chain of polymers363940 Since the electron-withdrawing

effect of fluorine atoms existed in 6FBPA can maximize

the hydrogen-bond acidity of hydroxyl groups ie the

hydrogen-bond basicity of hydroxylic oxygen atoms can

be minimised itrsquos considered as a promising candidate

for gas sensing material by hydrogen-bonding interac-

tion And itrsquos a great challenge to combine this sensing

material with SWNTs for explosive CWAs and relative

compounds sensing especially for dimethyl methylphos-

phonate (DMMP) through the hydrogen-bonding interac-

tion (shown in Fig 1)

Therefore in the present study 6FBPA has been firstly

attached onto the surface of SWNTs Due to the strong

hydrogen-bonding interaction between 6FBPA sensing

groups and DMMP the resultant chemical sensor exhib-

ited higher sensitivity and selectivity compared with the

bare SWNTs based sensors The achievement of SWNT-

6FBPA hybrids sensing materials with high performance

is expected to pave a new avenue toward the realization of

low cost low power and portable sensing device system

2 EXPERIMENTAL DETAILS

21 Materials

The 6FBPA (98) was obtained from Alfa-Aesar and used

as received DMMP (97) was obtained from Sigma-

Aldrich All of other chemicals (analytical reagent grade)

were purchased from Shanghai Chemical Reagents Co

Ltd (China) SWNTs used in this study were synthesized

by the arc discharge method All of organic solvents were

purified by distillation

22 Purification of SWNTs

The purification of SWNTs was executed by air oxidation

at 365 C for 30 min followed by refluxing with a 31

mixture of concentrated sulfuric acid and nitric acid at

80 C for 30 min As a result of the purification process

carboxylic groups are associated with the defect sites and

the terminated carbons in chemically shortened nanotubes

The purified SWNTs contain sim4 carboxylic acid groups

as estimated by acid-base titration4142 The final purified

SWNTs have a purity of about 95

23 Preparation of SWNT-6FBPA Hybrids Material

The procedure for the preparation of SWNT-6FBPA

hybrids is based on the methodology already demonstrated

by several authors4344 The typical approach was as fol-

lows (Fig 2) 300 mg purified SWNTs were suspended in

40 mL thionyl chloride (SOCl2) and 1 mL dimethyl for-

mamide (DMF) These suspensions were refluxed at 65 Cwhile keeping stirring for 24 h The black solid was then

separated by filtration and washed with anhydrous tetrahy-

drofuran (THF) several times Subsequently it was vac-

uum dried at room temperature for 1 h As a result the

acylated SWNTs were obtained 100 mg of SWNTs with

acyl chloride groups were mixed with 200 mg of 6FBPA in

DMF which was freshly distilled at reduced pressure The

mixture was ultrasonicated for several minutes and 1 mL

of pyridine was added the reaction was allowed to take

place by keeping stirring for 24 h at room temperature

The resultant suspension was separated by filtration with

the same 022 PTFE membrane filter Followed by thor-

oughly washing with DMF and alcohol and finally dried

overnight in the vacuum oven at 60 C

24 Fabrication of SWNT-6FBPA HybridizedSensing Devices

The standard microfabrication procedures were carried out

to obtain the electrodes for the sensors array here The

interdigitated electrode fingers were made by sputtering

10 nm Cr and 180 nm Au onto a patterned photoresist

mold A lift-off process was further introduced to remove

the photoresist The resultant electrodes were sonicated

in ethanol washed with deionized water thoroughly and

finally dried by nitrogen flow

In order to fabricate the SWNT-6FBPA hybrids sens-

ing devices the typical protocols have been designed as

follows the as-prepared SWNT-6FBPA hybrids were sus-

pended in DMF (01 g mLminus1) and ultrasonicated for 2 h

in order to make sure the hybrids had been efficiently dis-

persed in DMF Subsequently 01 L of the above solution

was extracted and deposited onto the electrode gap using

a microsyringe After evaporation of the solution through

putting the devices in the vacuum oven at 60 C for 1 h a

network of SWNT-6FBPA hybrids bridged each electrode

gap could be formed Further thermal treatment at 150 Cin the vacuum oven for 1 h was executed in order to opti-

mize the contact between SWNTs and the gold electrodes



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



25 Characterization

















age was 200 kV





















onto the SWNTs



































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)



of bare SWNTs


































tube structure













Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)


(c) O1s











(c) alcohol













controller








Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



























(a)

(b)


























Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



25 Characterization

















age was 200 kV





















onto the SWNTs



































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)



of bare SWNTs


































tube structure













Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)


(c) O1s











(c) alcohol













controller








Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



























(a)

(b)


























Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)



of bare SWNTs


































tube structure













Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)


(c) O1s











(c) alcohol













controller








Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



























(a)

(b)


























Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE


(a)

(b)

(c)


(c) O1s











(c) alcohol













controller








Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



























(a)

(b)


























Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE



























(a)

(b)


























Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE






















(a)

(b)




concentrations




































trations of DMMP



Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400














































Tue 20 Mar 2012 015941

RESEARCH

ARTIC

LE







4 CONCLUSIONS


















Fund no 09520714400













































hexa”uorobisphenol a covalently functionalized single...

Documents