Sensing properties of sulfonated multi walled carbon nanotube and graphene nanocomposites with polyaniline

Original ArticleSensing properties of sulfonated multi-walled carbon nanotube and graphene nanocomposites with polyaniline Department of Applied Chemistry, Faculty of Engineering and Tec

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Original Article

Sensing properties of sulfonated multi-walled carbon nanotube and

graphene nanocomposites with polyaniline

Department of Applied Chemistry, Faculty of Engineering and Technology, Aligarh Muslim University, Aligarh, 202002, India

a r t i c l e i n f o

Article history:

Received 27 September 2018

Received in revised form

2 February 2019

Accepted 3 February 2019

Available online 8 February 2019

Keywords:

In-situ polymerization

Pani/MWCNT and Pani/GN nanocomposite

Sulphonation

Isothermal and cyclic ageing technique

Amine identiﬁcation

a b s t r a c t

Here, we discuss one of the simplest approaches for chemical functionalization of in-situ prepared polyaniline (Pani) and its nanocomposites with multi-walled carbon nanotubes (MWCNT) and graphene (GN) in chlorosulphonic acid The effect of polymerization and functionalization was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis, Field emission scanning electron microscopy (FESEM) and electro-thermal analysis Results also revealed the presence ofpp

interactions between Pani and carbon allotropes leading to the formation of charge-transfer complexes This strongppinteraction signiﬁcantly increased the resultant electrical conductivity, stabilizing them

as well Further, theirs back to back sulphonation in chlorosulphonic acid signiﬁcantly enhanced the solubility in one way but caused a heavy loss in conductivity conversely The thermoelectric properties of the as-prepared nanocomposites were investigated as a function of MWCNT and GN contents It was observed that as-prepared Pani/GN nanocomposites showed a greater electrical conductivity as well as

an improved thermal stability in terms of DC electrical conductivity retention under isothermal and cyclic ageing conditions compared with Pani/MWCNT and Pani Finally these oxidative products were also studied for their sensing response towards amine to detect whether the particular compound is either 1, 2, or 3amine

© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

Limitless publications on 150 years old polyaniline and young

aged rapidly rising graphitic nanomaterials (i.e CNTs, graphenes,

fullerenes etc.)[1,2] have been evidently shown how they have

matured over the past few years with a very broad spectrum and

wide application range in engineering and medical sciences as well

as in their commercial & economical aspects Recently, their

nanocomposites possess the combination of high stability and fairly

good electrical conductivity due to the synergism between the

constituents[3] Despite the stubborn improvement ensued so far,

the backbone stiffness of polyaniline, limited solubility and stability

of MWCNT and graphene dispersions in water remains an ongoing

challenge complicating its processing, management and ultimately

the scope of their applications[4] On account of these issues and to

optimize their efﬁciency for use in various applications such as high

strength nanoﬁbres, sensors and nanoelectronic wires it has become of immense interest to attach some functional parts on their surface [5e7] These (covalent or non-covalent) surface modiﬁcations caused either by organic or inorganic species in general and especially by sulphonic groups highly enhanced their solubility, impart considerable stability and strong surface acidity making it highly useful for sophisticated electronic applications and excellent catalyst support for highly dispersed metal nano-particles[8e11]

That's the reason why the molecular functionalization has been the deep-seated interest of research world after the ingenious work

of Yue and Epstein[12]and persistently opening the door to un-precedented materials applications Covalent functionalization is comparatively more effective and greatly alters the electrical con-ductivity of polyaniline It introduces some defect sites forming a new type of nanostructures for diverse applications On the other hand, Hua Bai et al.[13]have reported a non-covalent functional-ization process involving the formation of charge transfer com-plexes due to the strongppinteractions between quinoidal units

of Pani and pyrenyl rings of MWCNTs or graphene Yue and Epstein [14] prepared self doped Pani almost two decades ago by the

* Corresponding author.

E-mail addresses: mahfooz55@gmail.com (M Khan), tariqalig001@gmail.com

(T Anwer), faizmohammad54@rediffmail.com (F Mohammad).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

https://doi.org/10.1016/j.jsamd.2019.02.002

Journal of Science: Advanced Materials and Devices 4 (2019) 132e142

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chemical modiﬁcation in the presence of fuming H2SO4and studied

their better solubility as well as redox activity and conductivity over

a wider pH range Deore et al.[15]prepared switchable self-doped

Pani with interconversion between self-doped and non-self-doped

forms Recently Zhang et al.[16]have reported the development of

water soluble nanocomposite of sulphonated polyaniline with

MWCNTs Their electrical parameters such as conductivity, thermal

stability, dielectric behavior etc have rarely been reported In this

work, we report our continued effort to make use of

chlor-osulphonic acid in an inert solvent instead of using fuming H2SO4

for sulphonation of Pani, Pani/MWCNT and Pani/GN

nano-composites Comparative studies on sensing performance and DC

electrical conductivity retention were also done to ascertain ef

ﬁ-ciency for their potential applications in the latest sophisticated

technologies

2 Experimental

2.1 Materials used

Monomer “aniline” from E-Merck India Ltd was puriﬁed by

distilling twice before use The MWCNT (diameter and average

lengths were about 10e20 nm and 20mm respectively) and

gra-phene used in this study were purchased from Iljin Nano Tech,

Seoul, Korea Potassium persulphate (PPS) and HCl (AR grade) and

methanol were purchased from (CDH India Ltd.) and were used as

received Double distilled water (DDW) was used in all the

exper-imental procedures and washing

2.2 Preparation of Pani, Pani/MWCNT and Pani/GN

nanocomposites

The nanocomposites of Pani/MWCNTs were prepared by in-situ

oxidative polymerization Firstly, 200 mL of 1M HCl and 5 mL

an-iline were added dropwise under stirring The ultrasonicated

sus-pension of MWCNTs (0.15 gm in 100 mL of 1M HCl) was transferred

into aniline solution The oxidant was readied by dissolving 14.8 gm

K2S2O8in 200 mL of 1 M HCl The polymerization was effected by

dropwise adding the oxidant solution into the aniline/MWCNTs

suspension and left for stirring continuously for about 16 hours The

resultant greenish black slurry wasﬁltered and washed thoroughly

with 2.5 L double distilled water to remove the excess acid as well

as oxidant until the ﬁltrate became colorless Thus prepared

nanocomposites was dedoped by aqueous (IM) ammonia to convert

it into emeraldine base (EB) form The Pani/MWCNTs (EB) was dried

around 70C for 4 hours in an air oven, converted intoﬁne powder

and was stored in a cool and dry place for further investigations

Pani (EB) as well as Pani (EB)/GN nanocomposites were also

pre-pared using the same method

2.3 Sulphonation of Pani, Pani/MWCNT and Pani/GN

nanocomposites

The prepared Pani (EB) was sulphonated by using

chlor-osulphonic acid 2 gm of as-prepared Pani (EB) powder was

dispersed in 200 mL of 1, 2-dichloroethane (DCE) and constantly

stirred at 75C Thereafter, 3.5 gm of chlorosulphonic acid diluted

with 10 mL of DCE was added dropwise in 20 min and the reaction

mixture was left for 4 hours The resultant greenish suspension was

ﬁltered, kept in 100 mL water and heated for 6 hours at 75C to

promote its hydrolysis Finally, theﬁlter cake was washed with 1 L

water, followed by 200 mL methanol, dried in an air oven at 70C

and was transformed into sulphonated Pani (S-Pani) Similarly

sulphonated Pani/MWCNTs (S-Pani/MWCNTs) and sulphonated

Pani/GN (S-Pani/GN) were prepared using the same method and

were stored in an airtight sample container for characterized further studies

2.4 Characterization Surface morphologies of Pani (EB), Pani (EB)/MWCNT and Pani (EB)/GN (gold coated) were viewed under a scanning electron mi-croscope (SEM) (LEO 435-VF) Their phase composition was analyzed by X-ray diffraction (XRD) recorded by Bruker D8 diffractometer with Cu Ka radiation at 1.540 Å in the range of

5 2q 70 at 40 kV The FT-IR spectra were recorded using

Perkin-Elmer-Spectrum 2000 Spectrophotometer in KBr between

400 and 4000 cm1 The electrical conductivity as well as thermal stability in terms of DC electrical conductivity retention were studied according to the method already reported[17]using the equation:

Ds¼ ½ln 2ð2S=WÞ =½2pSðV=IÞ (1) where I, V, W and S are the current (A), voltage (V), the thickness of the pellet (cm) and probe spacing (cm) respectively andsis the DC electrical conductivity (S cm1)[17]

3 Results and discussion 3.1 The formation of S-Pani, S-Pani/MWCNT and S-Pani/GN The proposed novel balanced chemical equation and formation scheme of Pani (EB) and its sulphonation has been summarized below Here,ﬁrst of all Pani (EB) was prepared by simple oxidative polymerization whereas Pani (EB)/MWCNT and Pani (EB)/GN were also prepared in the same way by additional use of MWCNT and graphene nanosheets These in-situ products were dried and then treated with chlorosulphonic acid (HSO3Cl) at 75CFig 1(a) Dark green free ﬂowing powders were obtained expecting to achieve 50% sulphonation Achievement of 100% sulphonation has not been reported so far to the best of our knowledge but it would be pre-dicted to have considerably greater water solubility Similarly, S-Pani/MWCNT and S-Pani/GN nanocomposites can be produced in Fig 1(b,c)

3.2 Conﬁrmation for sulphonation Color change test was carried out to get conﬁrmation whether as prepared products have undergone sulphonation or not For this, these chlorosulphonic acid treated products were dissolved in ammonia solutionFig 2 It was observed that the color of the so-lution turned blue within few seconds indicating the process of undoping When these undoped solutions were heated at 100C, the color of the solution mixtures returned back to greenish black due to volatilization of ammonia vapors This evidently proves that chlorosulphonic acid treated products had undergone sulphonation

3.3 FTIR spectroscopic studies Pani (EB), Pani (EB)/MWCNTs and Pani (EB)/GN and their sul-phonated products were characterized by FTIR to study the in-teractions between comprising constituents The peaks at 1620 and

1560 cm1(corresponding to quinoid and benzenoid ring respec-tively), 1338 cm1(C-N stretching), 1205 cm1(C¼N stretching), and 823 cm1(1,4-substituted phenyl ring stretching) are charac-teristics of EB form of PaniFig 3 [18,19] Likewise, FTIR spectra of Pani/MWCNTs and Pani/GN are almost identical to Pani except all their peaks have slightly shifted to higher wavenumbers This

M Khan et al / Journal of Science: Advanced Materials and Devices 4 (2019) 132e142 133

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Fig 1 Formation of S-Pani (a), S-Pani/MWCNTs (b) and S-Pani/GN (c).

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seems to be due to theppinteraction between quinoid rings of

Pani and pyrenyl rings of graphitic materials

On the other hand, if comparing these spectra with those of

their corresponding sulphonated counterparts, we observe that the

sulphonation has caused the band broadening in all the cases The

presence of characteristic peaks at 1090 and 1015 cm1matching to

the asymmetric and symmetric O¼S¼O stretching vibrations

respectively verify the presence of sulfonic groups covalently

bound to the polymer backbone [20] The presence of SeO

stretching peak at 730 cm1 also supports the sulphonation of

Pani, Pani/MWCNTs and Pani/GN

3.4 Surface morphology

The FE-SEM images of Pani, Pani/MWCNTs, Pani/GN and their

sulphonated products are shown inFig 4at different magni

ﬁca-tions Pani (Fig 4a) seems to have“Lima” bean shaped curved

structure, whereas Pani/MWCNTs have somewhat more

elon-gated tubular morphology indicating polymerization of aniline

over MWCNTs (Fig 4c) In the case of Pani/GN,ﬂaky sheets are

being observed which indicates the deposition of polyaniline over

graphene nanosheets The existence of MWCNT and GN can be

evidently seen and act as a conductive pathway for electron

car-rying which interconnects among Pani coated with Pani/MWCNTs

and Pani/GN to hinder close stacking and improve electrolyte ions

accessibility It seems that the sulphonation of Pani beans trans-formed them into granular structures In case of S-Pani/MWCNTs and S-Pani/GN (Fig 4d,e),eSO3H groups seems to have attached with Pani chain encapsulating the MWCNTs and GN respectively [21]

4 Electrical properties Electro-thermal studies of all as-prepared Pani, Pani/MWCNTs, Pani/GN and their sulphonated products were well carried out by standard 4-in-line probe technique in the temperature range of

40Ce150C As-prepared Pani, Pani/MWCNTs, Pani/GN (EB) are

doped with H2SO4in which Hþions act as a dopant and sulpho-nation (covalent attachment of eSO3H) Results of the electrical conductivity measurements indicate the p-type semiconducting behavior of all the materials within the operating temperature range of the experiment It was also observed that the addition of MWCNTs and GN has caused the augmentation in their electrical conductivities as shown inFig 5 Since the Pani as well as infusing graphitic nanoﬁllers MWCNTs and GN) are good conducting, the enhancement in DC electrical conductivity may be credited to the additive synergism of both the constituents interacting at the molecular level Although, both MWCNTs and GN are nearly matching in their chemical makeup and mechanical properties, graphene has been observed to be far better than MWCNTs in Fig 2 Color change test for self-doped S-Pani.

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contributing its exceptional attributions (like electrical

conductiv-ity, strength etc.) to the host polymer matrix [22] Both the

MWCNTs and GN are derived from graphite but the mobility of

electrons is higher in GN making it more electronically conducting

than MWCNTs That's why the nanoﬁller loading of Pani by

MWCNTs and GN have caused a promising augmentation in

elec-trical conductivity Besides, the strong pp-ppinteraction between

thep-bonded surface of the carbon based nano scaled materials

and the conjugated structure of Pani also imparts the enhancement

of the conductivity up to some extent

But contrary to that, sulphonation (covalent attachment of

eSO3H) to Pani and its nanocomposites with either MWCNTs or GN

one, has caused a promising cutback in electrical conductivity of all

the three S-Pani, S-Pani/MWCNTs as well as S-Pani/GN This seems

to be because of the low extent of doping

4.1 Isothermal ageing

The isothermal investigation in terms of DC electrical

conduc-tivity retention of prepared materials would be a key component in

analyzing their thermal stability FromFig 6, it may be seen that the

as-prepared Pani as well as Pani/GN showed a signiﬁcant increase

in loss in DC electrical conductivity with increasing the

temperature On the other hand, Pani/MWCNTs showed a little initial gain up to 80C and thereafter a comparatively lower loss in conductivity with increase in temperature This may be due to the inclusion of MWCNTs which may interact with Pani by different fashions causing somewhat irregularities in their behavior In addition, it causes also the low thermal stability and the insolubility

in water This polymerization pathway is sulphonated for the for-mation of the soluble and thermally stable in a common polar solvents and water

It was observed that the S-Pani/GN showed a signiﬁcant decrease in the magnitude of either loss/gain leading towards the better thermal stabilization as compared with the S-Pani/MWCNTs This seems to be because of the fact that GN has (a) theﬂat ge-ometry, (b) the high mobility of charge carriers and (c) the very high density of surface defects etc as compared to MWCNTs These extraordinary properties of GN may facilitate the interaction of Pani with incoming sulphonic groups and thus strengthening the ther-mal stability of as-prepared nanocomposites much more than that

of MWCNTs

The change in the relative electrical conductivity in each experiment was divided by the pratical duration (20 min) to get electrical conductivity loss/gain per minute of heating as given by the following equation:

Fig 4 FE-SEM images of (a) Pani (b) S-Pani (c) Pani/MWCNTs (d) S-Pani/MWCNTs (e) Pani/GN and (f) S-Pani/GN.

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where Ds ¼ change in relative electrical conductivity/min,

sf ¼ ﬁnal relative electrical conductivity at temperature T,

si¼ initial relative electrical conductivity at temperature T andDt is

duration of experiment (20 min)

Hence, it may be inferred that the S-Pani/GN is thermally more

stable as compared to S-Pani/MWCNTs and has better solubility in

water holding greater promise in theﬁelds of thermoelectric race

4.2 Cyclic ageing

A bar graph showing cyclic ageing process of Pani, Pani/

MWCNTs, Pani/GN and their sulphonated derivatives have been

demonstrated inFig 7 It was observed that loss/gain in

conduc-tivities of sulphonated products was much lesser than those

sam-ples which were not treated with chlorosulphonic acid It seems

that the sulphonation (covalent attachment ofeSO3H) has replaced

the free charge carriers in S-Pani, S-Pani/MWCNTs and S-Pani/GN

and remain covalently intact with them causing enhancement in

thermal stability

5 Sensing studies The fundamental and principle enabling Pani to be used as chemosensory is how either dopants or other reagents interact with it's producing charge carriers responsible for electrical con-duction This interaction at the molecular level affects the number and the movement of charge carriers along the chain Design of a simple, low cost and portable novel gas sensing device based on small changes in conductivity in response to the binding of analysts has been reported here Ansari et al.[17]in their nanocomposite of polyaniline with TiO2has described the sensing response towards ammonia with a good response as well as a fast recovery Presently,

we are continuing to deal with this interaction not limiting to ammonia only but also for amines 1, 2or 3

5.1 Treatment offilm for sensing Thefilms for sensing were prepared by dissolving powders of Pani, Pani/MWCNTs and Pani/GN in the N-Methyl-2-pyrrolidone (NMP) solution by a sonicator Then, it is casted on a round shape Petridis and is put in the oven at 70 C till the solvent (NMP) evaporated After that it is taken out in the form offilm Fig 5 Initial DC electrical conductivity of: (a) Pani (b) Pani/MWCNTs (c) Pani/GN (d) S-Pani (e) S-Pani/MWCNTs and (f) S-Pani/GN.

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by a very cheap and best methodology As-preparedﬁlms doped

in a hydrochloride solution (1M) Furthermore, they were taken

out in 2 hrs and then dried at room temperature These ﬁlms

were then put inside the test box of 4-probe and, were

alter-nately exposed to the ambient air, vapors of ammonia and

corresponding amines for deprotonation In this case, notable

changes in response were observed

There are a lot of articles reported the increase of the

conduc-tivity of polyaniline with the acid added and the decrease in the

basic atmosphere But herein, we have observed an unusual

phe-nomenon in juxtaposition to the above mentioned assumption

This seems to be because of the fact that the preparation of

poly-aniline was carried out in the acidic medium and thus obtained

products were usually emeraldine salts which are good conducting

in nature When these emeraldine salts are allowed to come in

contact with basic atmosphere, there are possibilities for the

for-mation of several redox forms of Pani, such as leucoemeraldine

base (non conducting), emeraldine base (half-oxidized form),

conducting emeraldine salt (half-oxidized and protonated form),

and pernigraniline base (fully oxidized form)[23] Therefore, its

mechanism of gas sensitivity exposed to vapor molecules would

obviously be complex[24]

The sensing mechanism depends upon the types of interactions

which are involved, i.e strong chemical bond formation or weak

hydrogen bonding, van der Waals force etc., between the sensing

ﬁlm and adsorbed vapor molecules It is well known that for a

strong interaction system, the recovery is generally very difﬁcult,

but in case of weak interactions, the recovery is easy even at room

temperature Since we have observed here both the recovery as

well as the reproducibility but with a constant decrease in

magnitude That's the reason that there are possibilities of both

types of interactions

In brief, it can be concluded that there are two processes which

are in operation The ﬁrst one is the irreversible acid-base

compensation or electrical neutralization of the Pani backbone

and the second one is the reversible chemisorptions of amines with

Pani In case of the irreversible acid/base neutralization the

mechanism is simple (based on the protonation and deprotonation

process) and the conductivity decreases in basic conditions and

gets increased in ambient air Herein, when Pani is exposed to low concentration of amines, the positive charge carrying nitrogens in the emeraldine salt play some acid-base chemistry leading to the undoping of the Pani The lone pair of electrons existed on amines thus interacts with the positive site of Pani This causes the decrease

in the intensities of the positive charge carriers (holes) as well as their mobility resulting in the decrease in electrical conductivity [17] Iin case of reversible chemisorption process it can be inferred that when nitrogen of ammonia comes in contact with the emer-aldine salt of Pani, it forms a temporarily unstable complex leading

to the decrease in electrical conductivity Whereas if the process is reversed and emeraldine salt form of Pani is provided at the ambient environment, then the previously formed temporary complex breaks down into their constituents causing regain in electrical conductivity But the unusual electrical behavior of Pani observed here, in some cases of our studies, seems to be attributed

by several factors like the presence of electron releasing groups, steric hindrance, the van der Waals interactions etc

5.2 Effects of ammonia and their derivatives (1, 2and 3amines)

on the electrical response of the Pani, Pani/MWCNTs and Pani/GN sensor

5.2.1 The selectivity The effects of ammonia, methylamine (Ma), dimethylamine (Dma), and trimethylamine (Tma) on the electrical response of the sensor are shown inFig 8 From this ﬁgure, it seems that the response magnitude as well as the response rate decrease in some cases and in a few cases they increases with time Thus the different electrical response of the same Pani sensor towards vapor mole-cules of different derivatives of ammonia was observed On account

of these differences in results, Pani chemosensor might be used to distinguish ammonia and some similar vapors of their derivatives (1, 2 and 3 amines) with the help of so designed sensor arrangement[25]

5.2.2 Factors affecting electrical response

It is well established that in methylamine, dimethylamine and trimethylamine, one, two and/or three electron releasing groups

Fig 7 Changes in the electrical conductivity/cycle of: (a) Pani, (b) Pani/MWCNTs, (c) Pani/GN, (d) S-Pani, (e) S-Pani/MWCNTs and (f) S-Pani/GN under cyclic ageing.

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(-CH3) are attached respectively which creates different electron

density at the incoming nitrogen atom This difference in electron

density causes the dissimilarity in the interaction of sensorﬁlm

with adsorbed gas molecules, resulting in the variation of observed

conductivity This is the effect of electron releasing groups (þI

effect)

Effect of steric hindrance: There are the so-called the effect of

steric hindrance There, the nitrogen atom responsible for

interac-tion are more hindered in 3amine than in 2and 1

We also know that the N-atom of the emeraldine salt is radical

cation and is very small in size which causes polarization and will

create induced dipole moments in the incoming vapor molecules

and there would be possibilities of strong van der Waal's

interac-tion between them It was also observed that increment in

elec-trical conductivity also depends upon the degree of polarizing

power of the cation radical and polarizability of the incoming

electron rich molecule The higher the polarity of the vapor the more is the conductivity increased This is the effect of polarization These all above mentioned reasons are seemed to be the possible cause for out of the ordinary behavior in electrical con-ductivity of Pani sensorﬁlm in the basic environment and ambient air But in our viewpoint, the unusual behavior of the electrical conductivity largely depends upon the strong interaction of the van der Waal's force resulting from the grain boundary effects

5.2.3 Reproducibility The reversible chemisorption process based on the physical adsorption and the desorption process causes a change in the conductivity of the sensorﬁlm attributing to its reproducibility The noteworthy changes in conductivities of as-prepared materials on the exposure to different concentrations of aqueous ammonia and amines at room temperature as a function of time are observed We Fig 8 Conductivity variation of the in-situ polymerized Pani ﬁlm on exposure to (a) ammonia (b) methylamine (c) dimethylamine and (d) trimethylamine.

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have systematically investigated several samples of Pani, Pani/

MWCNTs and Pani/GN for their sensing response to ammonia as

well as amines which can be looked into one by one in theFigs 9

and 10 It can be seen that almost all as-prepared materials

showed the worth mentioning response but with different paces

The conductivity could also be recovered uponﬂushing with the

ambient air Along with this reproducibility, they were observed to

have excellent reversibility, stability and selectivity toward NH3gas

over their derivatives which are of immense importance for their

potential applications in designing of efﬁcient and novel portable

sensing devices[26,27]

To investigate the reversibility of the gas sensor so designed, ﬁrst of all, the as-prepared Pani was repeatedly exposed to ammonia gas It was observed that on exposure of Pani to ammonia vapor, the process of chemisorption starts occurring Here in, when nitrogen of ammonia comes in contact with the emeraldine salt of Pani, it forms a temporarily unstable complex leading to the decrease in electrical conductivity But when the process is reversed and emeraldine salt form of Pani is provided at the ambient environment then the previously formed temporary complex breaks down into their constituents causing regain in electrical conductivity

Fig 9 Interaction and conductivity variation of Pani/MWCNTs ﬁlm on exposure to (a) ammonia (b) methylamine (c) dimethylamine and (d) trimethylamine.

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It was observed that the extent of the recovery was constantly

decreasing with increase in time as indicated by the continuous

decrease in the amplitude of damped oscillation This regular

decrease in the recovery of gas sensor may be attributed to the

regular consumption of active sites of Pani with constant rate and

lastly because of the insufﬁcient numbers of reacting sites available

for ammonia moiety to reform the complex structure required for

obtaining the recovery response From the decrease in amplitude as

shown in the graph, it can be inferred that with an increase in time

slight irreversibility starts occurring which is due to the electrical

compensation of the Pani backbone by ammonia

6 Conclusion

In summary, we have successfully prepared Pani and its

nano-composite with MWCNTs and GN via the oxidative polymerization

Reinforcement of both MWCNTs and GN in Pani has dazzlingly

enhanced their DC electrical conductivity but the result was more fruitful for graphene Furthermore, effective supplementation of functional groups -SO3H to the polyaniline surface of these in-situ products has brightly improved their solubility thus openined new possibilities for their prospective technological applications How-ever, ironically it has caused a heavy cutback in conductivity of all the products This may probably due to the replacement of ionic charge carriers by the covalently induced -SO3H After detailed studies of characteristics and sensing properties,finally, the authors came to the conclusion that the infusion of graphene is much more effective than MWCNTs Thus, it may be postulated that mingling of graphene can be thought out as an universal approach to prepare nanocomposites with enhanced conductivity and better solubility, which mayfind more realistic applications in modern electronic devices and seems to be a replaceable alternate even for metals in next generation We are looking forward to continued explosive growth in thisfield

Fig 10 Conductivity variation of in-situ polymerized Pani/GN ﬁlm on exposure to: (a) ammonia (b) methylamine (c) dimethylamine and (d) trimethylamine.

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