research article ammonia sensing by pani-dbsa based...

Research ArticleAmmonia Sensing by PANI-DBSA Based Gas SensorExploiting Kelvin Probe Technique

Anju Yadav123 Ajay Agarwal12 Pankaj B Agarwal12 and Parveen Saini23

1CSIR-Central Electronics Engineering Research Institute Pilani 333 031 India2Academy of Scientific amp Innovative Research (AcSIR) New Delhi 110 012 India3Polymeric and Soft Materials Section CSIR-National Physical Laboratory New Delhi 110 012 India

Correspondence should be addressed to Parveen Saini pksaininplindiaorg

Received 8 June 2015 Accepted 25 October 2015

Academic Editor Raphael Schneider

Copyright copy 2015 Anju Yadav et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI-DBSA) has been synthesized by chemical oxidative polymer-ization of aniline monomer in the presence of DBSA The UV-visible spectroscopy and X-ray diffraction measurements confirmthe formation of PANI and its doping by DBSA SEM images show the formation of submicron size rod shaped PANI particlesA vibrating capacitor based ammonia gas sensor was prepared by spin coating PANI-DBSA film over copper (Cu) substrate Thesensor exploited Kelvin probe technique to monitor contact potential difference between PANI and Cu as a function of time andammonia concentration Upon exposure to 30 ppm ammonia the sensor displays response time of 329 s recovery time of 3600 sand sensitivity value of 154 along with good repeatability

1 Introduction

Ammonia has vast applicability like use in agriculturalsector chemical industries medicinal fields refrigerationsystems and so forth [1ndash4] However due to its toxic natureapplication of ammonia also contributes to air pollutionThehazardous effect of ammonia can be felt around few hundredppm gas concentration [5] Its pungent odor and irritationeffect start to affect the human beings below 50 ppm level[2 6 7] Therefore there is a need for the developmentof ammonia gas sensor for timely detection of ppm levelconcentrations of ammonia

In the past metal oxides based ammonia gas sensors havebeen developed with fast response and high sensitivity [8 9]However they have disadvantages like complex fabricationsteps high power consumption high temperature operationand so forth [7 10 11] In this context conjugated polymersand their nanocomposites have shown great promise as gassensing material due to advantages in terms of facile synthe-sis tunable electrical and optoelectronic properties process-ing via solution route good sensitivity of their thin film basedsensor towards a number of acidicbasic gases improvedresponse recovery and sensitivity and most importantly

room temperature operation [7 12ndash17] Among variousconducting polymers polyaniline (PANI) is considered themost promising material for gas sensing purpose due to itslow monomer cost lab scale synthesis via chemical routeand flexibility in tuning of electrical properties particle mor-phology environmentalthermal stability and processabilityvia selection of dopant and adjustment of oxidation level[7 12 18 19] In particular its ability to undergo nonredoxdoping via protonic acid dopants and undoping by base inreversiblemannermakes PANI an ideal candidate for sensingof a number of toxic gases having acidicbasic character orelectron donatingaccepting nature [7]

In the past a number of papers reported the formationof PANI film based gas sensor that exploited change inresistance optical property resonance frequency or contactpotential difference (CPD) in response to ammonia gas orvapor [7 10 11 20 21] However there is no detailed report onthe PANI based ammonia sensor that measures gas exposureactuated changes in CPD between PANI layer and metallicsubstrate The CPD technique is considered advantageous asthere is no requirement of electrical contacts wire bondingor complicated fabrication steps [22]

Hindawi Publishing CorporationJournal of NanoparticlesVolume 2015 Article ID 842536 6 pageshttpdxdoiorg1011552015842536

2 Journal of Nanoparticles

This paper elaborates dodecyl benzene sulfonic acid(DBSA) doped PANI film based ammonia gas sensor whichmeasures change in work function of the PANI film uponexposure to ammonia The elongated PANI-DBSA particlesare prepared by oxidative polymerization and the formationof PANI and its existence in doped emeraldine salt (ES) formare ascertained by X-ray diffraction (XRD) and UV-visiblespectroscopy The morphology of PANI-DBSA is observedusing scanning electronmicroscopy (SEM) A sensing systemis formed by deposition of a layer of PANI-DBSA overcopper (Cu) substrate and the time dependent change inCPD between PANI and Cu is measured by Kelvin Probe forexposure to a given ammonia concentration The sensor istested for detection of ppm level concentration of ammoniagas and its sensing parameters (eg response time recoverytime and sensitivity) are measured

Materials Used Aniline (Loba Chemie) was freshlydouble distilled before use Ammonium persulfate (APS(NH4)2S2O8) dodecyl benzene sulfonic acid (DBSA)

(Acros) chloroform (Merck) and propanol (Merck) wereused on as-received basis Deionized water (resistivity gt106Ω-cm) was used for synthesis and washing

Synthesis of DBSA Doped Polyaniline DBSA doped PANI(ie PANI-DBSA) has been synthesized by chemical oxida-tive polymerization of aniline monomer via direct dopingroute using DBSA as dopant [23 24] The 01-mole anilinemonomer was mixed with 03M aqueous DBSA solution andthe mixture was cooled to 0∘C Polymerization was initiatedby the dropwise addition of aqueous solution of ammoniumpersulfate (01mol in 100mL deionized water) to reactionmixture and maintaining reaction mixture at 0∘C undercontinuous stirring After completion of polymerizationthe formed dark green emulsion of DBSA doped PANIwas deemulsified using propanol The resultant mixture wasfiltered through sintered glass crucible and the precipitateso obtained was washed repeatedly till the pH of the filtratebecame neutral Subsequently the filtered cake was dried andcrushed to obtain PANI-DBSApowder In the next step a cal-culated amount of PANI-BDSA was dispersed in chloroformby sonication followed by filtration through Whatman 41filter paper The filtered PANI-DBSAchloroform dispersionlayer (Figure 1) was formed over copper substrate (8mm lowast8mm) by spin coating at 1000 rpm

Characterization The optical spectra of the chloroform dis-persion of PANI-DBSAwere recorded usingUV-visible spec-trophotometer (Perkin Elmer lambda 25) in the wavelengthrange of 250ndash1000 nm X-ray diffraction (XRD) pattern wasrecorded using Bruker Advance D8 system in the diffraction(2120579) range of 10ndash80∘ usingCuK120572 (120582= 1540598 A) as radiationsource The scanning electron microscope (SEM Leo-440Carl-Zeiss UK accelerating potential 100 kV) was used toinvestigate the surface morphology of PANI-DBSA powderThe gas sensor characteristics were recorded using a Kelvinprobe gas sensing setup The ammonia gas at 30 ppm con-centration (ammonia-air mixture) was introduced into thetest chamber and changes in CPD between PANI film and

Figure 1 Spin coated PANI-DBSA layer over copper substrate

10 20 30 40 50 60 70 80

Cou

nts (

au)

2120579 (deg)

Figure 2 XRD pattern of PANI-DBSA powder

Cu substrate were recorded after every second using a dataacquisition system

2 Results and Discussions

21 X-RayDiffractionMeasurement Figure 2 shows the XRDpattern of DBSA-PANI powder that displays three dis-tinguished peaks at 2120579 values of 205∘ (119889 = 432 A)252∘ (119889 = 352 A) and 269∘ (331 A) In particular theexistence ofsim20∘ andsim25∘ peaks (which represent periodicityparallel and perpendicular to chain axis resp) confirms theformation of PANI Further the relative prominence of 25∘peak confirms the existence of PANI in its highly doped(electrically conducting) ES form which is expected to showgood sensitivity towards basic gases like ammonia

22 UV-Visible Spectroscopy Figure 3 shows the UV-visibleabsorption spectra of PANI-DBSA dispersion in chloroformThe spectrum consists of three distinguished transitionscentred on 346 nm (band-1) 431 nm (band-2) and 732 nm(band-3) wavelengths [23 25] Band-1 corresponds to 120587 rarr120587lowast transition of the benzenoid rings whereas band-2 and

band-3 are attributed to polaron rarr 120587lowast and 120587lowast rarr polaronictransitions respectively The prominence of band-3 com-pared to band-1 shows that PANI is formed in its dopedES form Exposure to basic gases like ammonia causes

Journal of Nanoparticles 3Ab

sorp

tion

400 500 600 700 800 900 1000300Wavelength (nm)

Figure 3 UV-visible spectra of PANI-DBSA dispersion in chloro-form

3120583m

Figure 4 SEM image of PANI-DBSA powder

partial undoping (shift towards emeraldine base ie EBform) leading to systematic variation of relative intensity andposition of these bands which forms the basis of opticalsensors Interestingly the undoping also leads to change inwork function (WF) of PANI such that WFES gt WFEBTherefore we exploited Kelvin probe technique to trace gasinduced variation of WF difference between PANI-DBSAlayer and Cu substrate

23 Morphological Investigations The SEM image of syn-thesized PANI-DBSA particles is shown in Figure 4 and itcan be seen that the formed PANI-DBSA particles displayrod-like structure with sim02 120583m diameter and sim1 120583m lengthThe decrease in particle size leads to increase in surface-to-volume ratio thereby exposing more sites for interactionswith incident gas Further the elongated particles are knownto display improved charge transport These factors areexpected to improve gas sensing response

24 Ammonia Sensing via Kelvin Probe Gas Sensing SetupThe Kelvin probe technique measures the change in workfunction (WF) in terms of change in contact potential (ΔCP)between the sample and reference electrode (gold tip) and not

VAC VACE

A

eCPD

WF1 WF2

EF

EF

120596

AC(120596)

+ minus

Figure 5 Schematic representation of Kelvin probe measurementprinciple

i

R

SC

E

V

V998400

eR

Figure 6 Circuit diagram of Kelvin probe measurement setup

as the absolute work function values [26] Figure 5 shows thecontact potential difference that corresponds to change inWFof material with respect to reference electrode

TheCPDmeasurement is based on the vibrating capacitorof Kelvin-Zisman [27] which is shown schematically inFigure 6

Here a capacitor is constituted by two electrodes the firstone is the sample mounted onto a piezoelectric ceramic thatwork as an active electrode (119878) whereas the other one is a goldtip based reference electrode (119877)This capacitorwith inherentcapacitance 119862 tends to charge under the influence of naturalcontact potential difference (119881) so that the developed charge(119876) can be expressed as

119876 = 119862119881 (1)

When the piezoelectric ceramic is polarized the sample(119878) is subjected to lateral vibration leading to the periodicchange of the capacitance which in turn induces a pseudos-inusoidal modulated current (119894) in the circuit This currentproduces an alternating voltage drop (119890

119877) across an external

resistor which is amplified via lock-in amplifier into a directvoltage 119864 which is the direct measure of the CPD changeunder the test gas In the beginning a counter potential 1198811015840


HN

HN N N

yx

H H HN

HN N N

yx

Conduction band

Valence band

Conduction band

Valence band

Polaron energy level

Vacuum level

WFES = 464 WFEB = 473

lowast

Xminus = DBSA Anion

NH4+

Xminus

NH4+

Xminus

NH3

+NH3

minusNH3

lowastlowastlowast

NH3

++

XminusXminus

Figure 7 Schematic representation of the ammonia mediated undoping of PANI-DBSA layer (top) and change in work function (bottom)

is manually adjusted to cancel the initial CPD to a zero valueunder the dilution gas

Gas sensing viaKelvin probe involves themeasurement ofvariation of CPD versus time for a given test gas concentra-tion [28] When layer of DBSA doped PANI (ES) depositedover Cu substrate is exposed to ammonia partial undopingconverts the ES toward emeraldine base (EB) formAs alreadydiscussed earlier such deprotonation induced undoping isaccompanied by change in work function of the PANI-DBSAlayer (shown schematically in Figure 7)

Figure 8 shows sensing response of PANI-DBSACu sub-strate sensing element at room temperature upon exposureto 30 ppm gas concentration Before exposure to ammo-nia the CPD was +005951 V However after exposure toammonia gas (30 ppm) CPD showed an abrupt decreasefollowed by exponential change to attain a saturation valueof minus0032227V

This can be ascribed to the sorption of ammonia gasmolecules on the surface of sensingDBSA-PANI layer leadingto deprotonation and change in oxidation level which tendsto increase the work function

During the recovery stage when ammonia supply wasstopped and dry air was passed through the system ammoniadesorption takes place leading to restoration of doped stateand original oxidation level These changes we observed interms of initial fast rise of CPD value followed by longexponential rise part The response and recovery time valuewere 329 sec and 3600 sec respectively The sensitivity of

1500 3000 4500 6000 7500 9000Time (s)

008

006

004

002

000

minus002

minus004

CPD

(V)

0

Figure 8 Repeatability curve of PANI-DBSA nanostructured filmtowards 30 ppm of ammonia

the sensor toward ammonia can be expressed in terms ofCPD values in the presence and absence of gas as

Sensitivity =(CPDAmmonia minus CPDDry Air)

CPDDry Air (2)

On the basis of CPD variation the sensorrsquos sensitivity for30 ppm ammonia is found to be 154 In order to observe

Journal of Nanoparticles 5

the reversibility and repeatability the sensor was subjected totwo sensing cycles (involving ammonia exposure saturationand recovery steps) keeping ammonia concentration at30 ppm for each cycle It was observed that in the secondcycle response and recovery times and sensitivity valueswere almost the same as in the case of the first cycle Thisdemonstrates the good repeatability of the sensor whichis extremely important for accurate detection and quan-tification of ammonia Nevertheless we feel that the CPDbased sensor is a relatively new concept and modificationsare expected in terms of active material designing filmforming techniques active layerrsquos morphology and selectionof substrate so that sensorrsquos responserecovery time as well assensitivity can be further improved

3 Conclusion

Submicron rod shaped particles of DBSA doped PANIhave been synthesized by oxidative polymerization andcoated onto copper substrate from chloroform solutionThe PANICu system is exposed to known ammonia con-centration and its CPD is monitored over the time viaKelvin probe technique The prepared gas sensor rapidlyand reversibly detects up to 30 ppm ammonia gas at roomtemperature conditions The sensor displayed response timeof 329 sec recovery time of 3600 sec and sensitivity valueof 154 with good repeatability Nanostructuring of PANImodulation of filmmorphology and thickness and formationof nanocomposites are expected to further improve thesensing characteristics of such sensors

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors wish to thank Director CSIR-NPL for accordingpermission to publish the workThe authors also thankDr NVijayan forXRDpatterns andMr KN Sood for SEM imagesThey are also thankful to Director CEERI for extendingKelvin probe facility Anju Yadav is thankful to CSIR for theaward of SRF

References

[1] httpenwikipediaorgwikiAmmonia[2] M Tajkarimi H P Riemann M N Hajmeer E L Gomez

V Razavilar and D O Cliver ldquoAmmonia disinfection ofanimal feedsmdashlaboratory studyrdquo International Journal of FoodMicrobiology vol 122 no 1-2 pp 23ndash28 2008

[3] httpwwwnytimescom20091004health04meathtmlpage-wanted=allamp r=0

[4] httpwwwwashingtonpostcomnationalhealth-scienceanhy-drous-ammonia-fertilizer-abundant-important-hazardous20130418c2d4c69c-a85a-11e2-a8e2-5b98cb59187f storyhtml

[5] ldquoVan nostrand reinholdrdquo Environmental Science amp Technologyvol 18 no 4 p 105A 1984

[6] B TimmerWOlthuis andA van den Berg ldquoAmmonia sensorsand their applicationsmdasha reviewrdquo Sensors and Actuators BChemical vol 107 no 2 pp 666ndash677 2005

[7] P Saini Ed Fundamentals of Conjugated Polymer BlendsCopolymers and Composites Synthesis Properties and Applica-tions John Wiley amp Sons New York NY USA 2015

[8] R Gosangi and R Gutierrez-Osuna ldquoActive temperature mod-ulation of metal-oxide sensors for quantitative analysis of gasmixturesrdquo Sensors and Actuators B Chemical vol 185 pp 201ndash210 2013

[9] N Barsan and U Weimar ldquoUnderstanding the fundamentalprinciples of metal oxide based gas sensors the example of COsensing with SnO

2sensors in the presence of humidityrdquo Journal

of Physics Condensed Matter vol 15 no 20 pp R813ndashR8392003

[10] J Janata and M Josowicz ldquoConducting polymers in electronicchemical sensorsrdquo Nature Materials vol 2 no 1 pp 19ndash242003

[11] H Bai and G Shi ldquoGas sensors based on conducting polymersrdquoSensors vol 7 no 3 pp 267ndash307 2007

[12] J Kumar M Shahabuddin A Singh et al ldquoHighly sensitivechemo-resistive ammonia sensor based on dodecyl benzenesulfonic acid doped polyaniline thin filmrdquo Science of AdvancedMaterials vol 7 no 3 pp 518ndash525 2015

[13] P Saini T Kuila S Saha and N C Murmu ldquo15 Graphene andits nanocomposites for gas sensing applicationsrdquo in AdvancedSensor and Detection Materials A Tiwari and M M DemirEds pp 467ndash500 John Wiley amp Sons 2014

[14] H S Nalwa Handbook of Organic Conductive Molecules andPolymers Wiley 1997

[15] U Lange N V Roznyatovskaya andVMMirsky ldquoConductingpolymers in chemical sensors and arraysrdquo Analytica ChimicaActa vol 614 no 1 pp 1ndash26 2008

[16] K C Persaud ldquoPolymers for chemical sensingrdquo MaterialsToday vol 8 no 4 pp 38ndash44 2005

[17] T K Das and S Prusty ldquoReview on conducting polymers andtheir applicationsrdquo PolymermdashPlastics Technology and Engineer-ing vol 51 no 14 pp 1487ndash1500 2012

[18] S Mikhaylov N Ogurtsov Y Noskov et al ldquoAmmoniaamineelectronic gas sensors based on hybrid polyaniline-TiO

2

nanocomposites The effects of titania and the surface activedoping acidrdquo RSC Advances vol 5 no 26 pp 20218ndash202262015

[19] S Bhadra D Khastgir N K Singha and J H Lee ldquoProgressin preparation processing and applications of polyanilinerdquoProgress in Polymer Science vol 34 no 8 pp 783ndash810 2009

[20] J Huang S Virji B H Weiller and R B Kaner ldquoNanostruc-tured polyaniline sensorsrdquoChemistrymdashAEuropean Journal vol10 no 6 pp 1314ndash1319 2004

[21] D Then A Vidic and C Ziegler ldquoA highly sensitive self-oscillating cantilever array for the quantitative and qualitativeanalysis of organic vapor mixturesrdquo Sensors and Actuators BChemical vol 117 no 1 pp 1ndash9 2006

[22] CMHangarterM Bangar AMulchandani andN VMyungldquoConducting polymer nanowires for chemiresistive and FET-based biochemical sensorsrdquo Journal of Materials Chemistryvol 20 no 16 pp 3131ndash3140 2010

[23] P Saini andM Arora ldquoFormationmechanism electronic prop-erties amp microwave shielding by nano-structured polyanilinesprepared by template free route using surfactant dopantsrdquoJournal of Materials Chemistry A vol 1 no 31 pp 8926ndash89342013


[24] P Saini R Jalan and S K Dhawan ldquoSynthesis and charac-terization of processable polyaniline doped with novel dopantNaSIPArdquo Journal of Applied Polymer Science vol 108 no 3 pp1437ndash1446 2008

[25] R Tas M Can and S Sonmezoglu ldquoPreparation and charac-terization of polyaniline microrods synthesized by using dode-cylbenzene sulfonic acid and periodic acidrdquo Turkish Journal ofChemistry vol 39 no 3 pp 589ndash599 2015

[26] J Abad and J Colchero ldquoMetal-conducting polymer interfacestudied byKelvin probemicroscopyAu andAl onpoly(3-octyl-thiophene)rdquo Journal of Polymer Science Part B Polymer Physicsvol 52 no 16 pp 1083ndash1093 2014

[27] E Souteynard D Nicolas and J R Martin ldquoSemiconduc-tormetalgas behaviour through surface-potential changerdquoSensors and Actuators B Chemical vol 25 no 1ndash3 pp 871ndash8751995

[28] D Nicolas E Souteyrand and J-R Martin ldquoGas sensorcharacterization through both contact potential difference andphotopotential measurementsrdquo Sensors and Actuators B Chem-ical vol 44 no 1ndash3 pp 507ndash511 1997

Submit your manuscripts athttpwwwhindawicom

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Biomaterials


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TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


This paper elaborates dodecyl benzene sulfonic acid(DBSA) doped PANI film based ammonia gas sensor whichmeasures change in work function of the PANI film uponexposure to ammonia The elongated PANI-DBSA particlesare prepared by oxidative polymerization and the formationof PANI and its existence in doped emeraldine salt (ES) formare ascertained by X-ray diffraction (XRD) and UV-visiblespectroscopy The morphology of PANI-DBSA is observedusing scanning electronmicroscopy (SEM) A sensing systemis formed by deposition of a layer of PANI-DBSA overcopper (Cu) substrate and the time dependent change inCPD between PANI and Cu is measured by Kelvin Probe forexposure to a given ammonia concentration The sensor istested for detection of ppm level concentration of ammoniagas and its sensing parameters (eg response time recoverytime and sensitivity) are measured

Materials Used Aniline (Loba Chemie) was freshlydouble distilled before use Ammonium persulfate (APS(NH4)2S2O8) dodecyl benzene sulfonic acid (DBSA)

(Acros) chloroform (Merck) and propanol (Merck) wereused on as-received basis Deionized water (resistivity gt106Ω-cm) was used for synthesis and washing

Synthesis of DBSA Doped Polyaniline DBSA doped PANI(ie PANI-DBSA) has been synthesized by chemical oxida-tive polymerization of aniline monomer via direct dopingroute using DBSA as dopant [23 24] The 01-mole anilinemonomer was mixed with 03M aqueous DBSA solution andthe mixture was cooled to 0∘C Polymerization was initiatedby the dropwise addition of aqueous solution of ammoniumpersulfate (01mol in 100mL deionized water) to reactionmixture and maintaining reaction mixture at 0∘C undercontinuous stirring After completion of polymerizationthe formed dark green emulsion of DBSA doped PANIwas deemulsified using propanol The resultant mixture wasfiltered through sintered glass crucible and the precipitateso obtained was washed repeatedly till the pH of the filtratebecame neutral Subsequently the filtered cake was dried andcrushed to obtain PANI-DBSApowder In the next step a cal-culated amount of PANI-BDSA was dispersed in chloroformby sonication followed by filtration through Whatman 41filter paper The filtered PANI-DBSAchloroform dispersionlayer (Figure 1) was formed over copper substrate (8mm lowast8mm) by spin coating at 1000 rpm

Characterization The optical spectra of the chloroform dis-persion of PANI-DBSAwere recorded usingUV-visible spec-trophotometer (Perkin Elmer lambda 25) in the wavelengthrange of 250ndash1000 nm X-ray diffraction (XRD) pattern wasrecorded using Bruker Advance D8 system in the diffraction(2120579) range of 10ndash80∘ usingCuK120572 (120582= 1540598 A) as radiationsource The scanning electron microscope (SEM Leo-440Carl-Zeiss UK accelerating potential 100 kV) was used toinvestigate the surface morphology of PANI-DBSA powderThe gas sensor characteristics were recorded using a Kelvinprobe gas sensing setup The ammonia gas at 30 ppm con-centration (ammonia-air mixture) was introduced into thetest chamber and changes in CPD between PANI film and

Figure 1 Spin coated PANI-DBSA layer over copper substrate

10 20 30 40 50 60 70 80

Cou

nts (

au)

2120579 (deg)

Figure 2 XRD pattern of PANI-DBSA powder

Cu substrate were recorded after every second using a dataacquisition system

2 Results and Discussions

21 X-RayDiffractionMeasurement Figure 2 shows the XRDpattern of DBSA-PANI powder that displays three dis-tinguished peaks at 2120579 values of 205∘ (119889 = 432 A)252∘ (119889 = 352 A) and 269∘ (331 A) In particular theexistence ofsim20∘ andsim25∘ peaks (which represent periodicityparallel and perpendicular to chain axis resp) confirms theformation of PANI Further the relative prominence of 25∘peak confirms the existence of PANI in its highly doped(electrically conducting) ES form which is expected to showgood sensitivity towards basic gases like ammonia

22 UV-Visible Spectroscopy Figure 3 shows the UV-visibleabsorption spectra of PANI-DBSA dispersion in chloroformThe spectrum consists of three distinguished transitionscentred on 346 nm (band-1) 431 nm (band-2) and 732 nm(band-3) wavelengths [23 25] Band-1 corresponds to 120587 rarr120587lowast transition of the benzenoid rings whereas band-2 and

band-3 are attributed to polaron rarr 120587lowast and 120587lowast rarr polaronictransitions respectively The prominence of band-3 com-pared to band-1 shows that PANI is formed in its dopedES form Exposure to basic gases like ammonia causes


sorp

tion

400 500 600 700 800 900 1000300Wavelength (nm)


3120583m





VAC VACE

A

eCPD

WF1 WF2

EF

EF

120596

AC(120596)

+ minus


i

R

SC

E

V

V998400

eR





119876 = 119862119881 (1)





HN

HN N N

yx

H H HN

HN N N

yx

Conduction band

Valence band

Conduction band

Valence band


Vacuum level

WFES = 464 WFEB = 473

lowast

Xminus = DBSA Anion

NH4+

Xminus

NH4+

Xminus

NH3

+NH3

minusNH3

lowastlowastlowast

NH3

++

XminusXminus







1500 3000 4500 6000 7500 9000Time (s)

008

006

004

002

000

minus002

minus004

CPD

(V)

0




CPDDry Air (2)




3 Conclusion




Acknowledgments


References





















2




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




sorp

tion

400 500 600 700 800 900 1000300Wavelength (nm)


3120583m





VAC VACE

A

eCPD

WF1 WF2

EF

EF

120596

AC(120596)

+ minus


i

R

SC

E

V

V998400

eR





119876 = 119862119881 (1)





HN

HN N N

yx

H H HN

HN N N

yx

Conduction band

Valence band

Conduction band

Valence band


Vacuum level

WFES = 464 WFEB = 473

lowast

Xminus = DBSA Anion

NH4+

Xminus

NH4+

Xminus

NH3

+NH3

minusNH3

lowastlowastlowast

NH3

++

XminusXminus







1500 3000 4500 6000 7500 9000Time (s)

008

006

004

002

000

minus002

minus004

CPD

(V)

0




CPDDry Air (2)




3 Conclusion




Acknowledgments


References





















2




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




HN

HN N N

yx

H H HN

HN N N

yx

Conduction band

Valence band

Conduction band

Valence band


Vacuum level

WFES = 464 WFEB = 473

lowast

Xminus = DBSA Anion

NH4+

Xminus

NH4+

Xminus

NH3

+NH3

minusNH3

lowastlowastlowast

NH3

++

XminusXminus







1500 3000 4500 6000 7500 9000Time (s)

008

006

004

002

000

minus002

minus004

CPD

(V)

0




CPDDry Air (2)




3 Conclusion




Acknowledgments


References





















2




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





3 Conclusion




Acknowledgments


References





















2




















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials
















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article ammonia sensing by pani-dbsa based...

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