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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 167

Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176ISSN:1410-8917

Jurnal Kimia-Sains &Aplikasi

e-ISSN:2597-9914

Jurnal Kimia Sains dan AplikasiJournal of Scientific and Applied Chemistry

Journal homepage: http://ejournalundip.ac.id/index.php/ksa

Electrocoating Polypyrrole on Gold-Wire Electrode asPotential Mediator Membrane Candidate for AnionicSurfactant Electrode Sensor H)

Check forupdates

Abdul Haris Watoni 3'1 *, Indra Noviandrib> 2, Muhammad Nurdin 3^,La Ode Ahmad Nur Ramadhan 3'4 *

a Department of Chemistry, Faculty of Mathematics and Natural Sciences, Halu Oleo University, Kendari, Indonesiab Department of Chemistry, Faculty of Mathematics and Natural Sciences, Bandung Institute of Technology, Bandung, Indonesia

* Author emails: (1,*) ahwatoni@gmail.com; (2) innov@chem.itb.ac.id; (3) mnurdino6@gmail.com; (4) ramadhan306@gmail.com

https://doi.0rg/10.14710/ jksa.23.5.167-176

Ar t i c l e I n f o Abs t r ac t

Article history:

Received: 6th February 2020Revised: 6thMay 2020Accepted: 7th May 2020Online: 31st May 2020

The development of polypyrrole as a potential mediator membrane candidate forsodium dodecyl sulfate (SDS) sensor electrode has been investigated. The polypyrrolemembrane was synthesized electrochemically from the pyrrole and coated at thesurface of a 1.0 mm diameter of the gold-wire electrode. Electropolymerization ofpyrrole and coating of the polypyrrole produced was performed by cyclic voltammetrytechnique in the electrochemical cell containing supporting electrolyte of 0.01 MNaC104 with an optimum potential range of -0.9 V-1.0 V, the scanning rate of 100

mV/s, an electric current of 2 mA, and running of potential scanning of 10 cycles. Byusing the similar optimal parameters of cyclic voltammetry, electropolymerization of0.01M pyrrole solution containing 0.001M SDS also produces a polypyrrole membranecoated at the gold-wire electrode surface. These coated electrodes have the potentialresponse-ability toward DS anions in the concentration range of 10 7 M-10 5 M with alimit of detection of 10 7 M and sensitivity of electrode of 9.9 mV/decade. This findingshows that the SDS solution’s role is as supporting electrolyte and also as a source ofDS dopant during the pyrrole electropolymerization processes. Dopants are trappedin the polymer membrane during the electrochemical formation of polypyrrole androle as ionophores for DS anion in the analyte solution. A potential response to theelectrode phenomena is excellent basic scientific information for further synthesis ofconducting polymer and development of conducting polymer-coated wire electrodemodel, especially in the construction of ion-selective electrode (ISE) for thedetermination of anionic surfactants with those models.

Keywords:polypyrrole;electropolymerization;coated wire electrode;anionic surfactant ISE

polymers to upgrade their application, primarily based ontheir morphology and electrical properties.

Polypyrrole (PPy) , a type of conducting polymer, hasionic and electronic conductivities [2, 3, 4, 5]. Theelectrical conductivity of polypyrrole is one of theessential properties for the development ofelectrochemical analysis techniques. Based on electricalconductivity, polypyrrole is studied in many fields ofstudy. These conducting polymers have environment

1. IntroductionConducting polymers is a unique and essential new

material because of its electrical, optical, and chemicalproperties. The electrical conductivity of the materialscan be increased from semiconductors, such as to theproperties of metals, by doping with appropriate dopants[1]. The advantage of conducting polymer over a newconcept of the charged material transport mechanism.The study of conducting polymer aims to modify

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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 168

stability [6, 7], electrolytic activity [8], and can be easilysynthesized [9]. In the electrochemical applications,polypyrrole is developed as electrode sensing material[10], catalyst in fuel cell [11], supercapacitor [12], andsolar cell [13].

The analyte potentiometrically determines one kindof analysis of the electrochemical method. Thisdetermination uses indicator electrodes to respond toanalyte ions and reference electrodes selectively. Theindicator electrode is equipped with a polymer membraneas an ionic exchange mediator between analyte ions withionophore ions trapped in the membrane. The ionicexchange equilibrium reaction takes place at themembrane interface and analyte solution. One indicatorelectrode studied today is the ion-selective electrode(ISE) of the coated wire electrode model. The coated wireelectrode has a small diameter of 0.5-2.0 mm so that itcan be applied on an intracellular scale of determinations[14]. With the size of the electrode, the determination ofanalyte ions using coated wire electrodes can be carriedout thriftier than that of using a tube electrode model.Based on the electric and ionic conductivity properties ofconducting polymer, it is expected that ISE constructedfrom conducting a polymer-coated wire model has betterperformance than the other models [15, 16].

The conducting polymer included polypyrrole, can besynthesized easily by chemical and electrochemicalmethods [17]. The deposition and coating of polypyrroleat the metal wire electrode surface were carried outduring the pyrrole electropolymerization by cyclicvoltammetry technique [18]. Using this technique, theelectron transfer process during the pyrroleelectropolymerization and the resulting polypyrrolemembrane coating can be studied from the indicatedcyclic voltammograms. Pyrrole electropolymerizationand the resulting polypyrrole coating must be carried outwithin a specific range of scanning potential, scanningrate, and certain cycles. Morphology and characteristicsof the polymer depend on trapped dopants, the solutionacidity, existing supporting electrolytes, and theconcentration of pyrrole monomers applied during theelectropolymerization processes [15, 19, 20]. Thosefactors influence the potentiometric characteristics of theresulting coated wire electrode [21]. The potentiometriccharacteristics of the electrode are also influenced by theconditioning system, such as the duration of theconditioning, the concentration of conditioning solution ,and the acidity of the solution [21, 22].

The conducting polymers, because of its ionic and itsconductivity, have an ionic transducer ability, which isgood for electrons in ionic sensor and biosensorelectrodes. It is found that the conductivity andmorphology of polypyrrole were also influenced bydopants trapped in the polypyrrole membrane matrix[23]. The electric conductivity of the membraneinfluences the rate of electron movement throughconducting membrane. While the morphology of

polypyrrole affects the ionic mobility of dopants and thephysical stability of the membrane, a metal-wireelectrode coated with polypyrrole membrane containinganionic surfactant dopants will shortly respond to thesame anion in the analyte solution [24]. Nevertheless, therelationship between membrane electrical conductivityand the sensitivity of the electrodes’ potential responsehas not been reported accurately.

During the measurement of anionic surfactant usingISE, a potential response resulting from the redoxmechanism is developed between the indicator electrodewith a reference electrode and equilibrium system at theinterface of electrode and analyte solution. At thoseinterfaces, an ionic exchange is developed betweendopant anions trapped in the polymer membrane with thesame anion of analyte surfactant. When the redoxreaction produces a constant potential difference and theconcentration of dopant anions in the polymer membraneis also constant, then, based on the Nernst equation, themeasured cell potential will only be influenced by theconcentration of surfactant anion in the analyte solution[24].

The aims of the research are to electrochemicalsynthesis and to directly coat polypyrrole membraneusing cyclic voltammetry technique and then to study thepotential of the polymer as a mediator membranecandidate for SDS surfactant potentiometric electrodesensor. Based on the results of the research, this paperreports the optimum parameters of cyclic voltammetryapplied for synthesis and coating polypyrrole at thesurface of the gold-wire electrode in the electrochemicalcell containing a mixed solution of pyrrole, NaC104 or SDSsupporting electrolyte, and DS anions as dopant species.The membrane was coated at the gold-wire electrodesurface during the pyrrole electropolymerization in thosemixed solutions. The gold-wire electrode coated with themembrane is then be used to measure the potentialresponse of DS anion in the SDS analyte solution.

2. MethodologyElectrochemical polymerization of pyrrole was

performed in electrochemical cells using the cyclicvoltammetry technique. All chemical materials andequipment used were available in Analytical ResearchLaboratory.

2.1. Materials

The primary materials used in this research were98% pyrrole solution as a monomer material ofsynthesized polypyrrole, sodium dodecyl sulfate (SDS) asstandard analyte solution, source of DS anion dopant ,supporting electrolyte, and conditioning solution forpolypyrrole coated gold-wire electrodes. Besides of SDSsurfactant, this research also used NaC104 solution as asupporting electrolyte during the electropolymerizationprocess. All those materials were purchased from SIGMA.Electrode materials used in electropolymerization

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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 169processes by cyclic voltammetry were gold (Au) wire asindicator electrode, platinum ( Pt) wire as the auxiliaryelectrode, and silver-coated silver chloride (Ag/AgCl) asthe reference electrode.

mixture of pyrrole, dopants, and supporting electrolytes.The cyclic voltammetry parameters observed were thepotential range of scanning and scanning rate.

The cyclic voltammetry of pyrroleelectropolymerization was performed by repeat potentialscanning from negative to positive and from reversedirection of potential value for ten cycles with an electriccurrent of 2 mA. These processes were performed in avoltammetric cell containing 0.01M pyrrole, 0.01M NaClsupporting electrolyte. The variation of potential range ofscanning observed were: (1) -0.5-1,0 V, (2) -0.6-1,0 V,(3) -0.7-1.0 V, (4) -0.8-1.0 V, (5) -0.9-1.0 V, and (6) -0.9-1.1 V, with scanning rate of potential of 50 , 80 , and100 mV/s, respectively. Electropolymerization was alsoperformed using a mixed solution of 0.01 M pyrrole and0.001MSDS.

2.2. Equipment

Some tools used to preparation of solution were 25-mL graduated cylinder, 25-mL graduated volumetricflask, 30-mL polyethylene bottle, and other standardglass equipment. Weighing of chemical materials wascarried out using an electric weighing of the METER AE200 model with an empty weight of 0.0000 g.

Electropolymerization and electrocoating of thegold-wire electrode were performed using a potentiostatIdlnstrument 400 model connected to a voltammetric cell.This cell was equipped with three electrodes: Ag AgClwith a diameter of 0.5 mm and length of 10.0 cm as areference electrode, platinum wire with a diameter of 0.2mm and length of 5.0 cm as the auxiliary electrode, andgold wire with a diameter of 1.0 mm and length of 5.0 cmas indicator electrode. These electrodes were dipped in avoltammetric cell containing a mixture solution ofpolymerization and were connected to a potentiostatmounted on a computer recording. The obtainedpolypyrrole coated gold wire electrodes were thenobserved to reveal and further develop its capability as aDS anion electrode sensor.

2.3.2. Potential electrode measurements

Polypyrrole coated gold-wire electrodes producedfrom this experiment are now called Au-PPy-DS. Beforeand after use for measurements, the electrodes weresoaked for a while in SDS solution to activate dopantstrapped in the membrane, activate ionic equilibrium atthe solution interface and membrane surface, and removeundesired site products electropolymerization reaction[21]. The electrodes were also soaked by tissue paper todry and to clean the impurity.

Au-PPy-DS and saturated calomel (Hg Hg2Cl2 3 MKC1) electrodes were then dipped in the analyte SDSsolution to measure the potential response of theelectrode toward DS analyte in the concentration rangeof 10 9 —10 2 M.The constant potential response producedfrom these measurements were recorded and plotted tothe negative logarithm of SDS concentration (pSDS) todetermine calibration curves, the limit of detection, andsensitivity of electrode. The electrode detection limit wasrecorded from the lowest concentration value of theextrapolated calibration curve, while the electrodesensitivity was recorded from the slope value of the linear(calibration) curve by mV/decade unit.

3. Results and Discussion3.1. Voltammetrically Electrocoating of Polypyrrole

It was observed that polypyrrole could besynthesized by the electrochemical method. Cyclicvoltammetry is the most used technique applied in thecharacterization of conducting polymer such aspolypyrrole. This technique is applied by scanning thepotential in the forward and reverse directions during theelectropolymerization oxidation-reduction process ofaqueous pyrrole solution. This electropolymerizationapplies an electric current to force a redox reaction causedby diffusion current only [25]. To prevent the appearanceof migration currents, a supporting electrolyte is added tothe aqueous pyrrole solution, an electroactive solutionhaving higher activity than analyte solution [25]. Theaddition of supporting electrolytes also aims to increase

Potentiometric measurements were performed usingpolypyrrole coated gold wire electrodes as workingelectrodes and Hg H &Ch as a reference electrode. Bothelectrodes were connected to the pH/Voltmeter ORION420A model and dipped in the 50-mL potentiometric cellcontaining a magnetic stirrer. The potential responsesobtained from the measurements were recorded from thepH/Voltmeter.

2.3. Experiments

Laboratory experiments carried out in this researchincluded electrochemical synthesis and electrodepositionof polypyrrole on the surface of the gold wire electrodesand observing the capability of the coated wire electrodesas sensor electrodes for analyte SDS surfactant.

2.3.1. Electrosynthesis and electrocoating ofpolypyrrole

The coating of the electrode with polypyrrole wascarried out in a continuous process of pyrroleelectropolymerization on the surface of the gold-wireelectrode using a cyclic voltammetric technique in anelectrochemical cell equipped with three electrodes. Inthose processes, the gold-wire electrodes were placed asworking electrodes. The gold-wire was rubbed by silicapowder to clean its surface before dipped into avoltammetric cell. Two other electrodes were platinumwires as auxiliary electrodes and Ag/AgCl as referenceelectrodes. The process of electropolymerization wascarried out in the 10-mL voltammetric cell containing a

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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 170

the solution electric conductivity. Electropolymerizationby cyclic voltammetry is inaccurate in the absence ofsupporting electrolyte. To prevent convection currents,electropolymerization with this technique is also carriedout in a non-stirred solution.The morphology of polymermembrane produced depends on electrolyte nature,scanning rate and potential of depositions, monomerconcentration, and pH of solution [19].

Polypyrrole electrocoating on the surface of thegold-wire electrodes by cyclic voltammetry was carriedout with variations in the potential range and thescanning rate. Pyrrole, C4H5 N, is a water-solubleconjugated monomer and undergoes redox reactionsunder specific potential range and scanning rate.Potential scanning can be done repeatedly from negativeto positive and vice versa. Under the negative to thepositive direction running off the potential scanning,pyrrole monomers are oxidized to cationic radicalmonomer. Dimers are formed under reverse direction bythe reduction reaction of the cation, and so on untilpolymer formed under the direction of the cycle ofperforming potential scanning repeatedly. The generalmechanism for the propagation of electrochemicallypolymer chain formation is described by the sequentialreaction , as shown in Figure 1[26].

The resulting polypyrrole is coated directly on thesurface of the gold-wire electrodes with a certainthickness. A typical cyclic voltammogram recorded froma polypyrrole formation depended on the solvent, thesupporting electrolyte used, and cyclic voltammetryparameters applied [27, 28].

Pyrrole electropolymerization is processed anddeveloped under a complex reaction mechanism. Someproblems of the polymer , such as the formation process,the formation mechanism , and the charge naturalization ,structure, properties, and synthesis conditions used, aredebatable today [27]. The complete mechanism ofpolypyrrole formation is obtained when there are noredox reactions from other species during pyrroleelectropolymerization,

electropolymerization process must be carried out undera specific potential range where the typical potential peakand the current peak will be read and separated fromthose of other species. This is why the researcher alwaysperforms electropolymerization processes in variouspotential ranges to obtain valid data.

In this study, cyclic voltammograms generated fromthe pyrrole electropolymerization process are presentedin various potential scanning ranges. It appears that theseparameters affect the oxidation and reduction of the peakpolymer current (Figure 2).

Based on the anodic and cathodic peak currentsshown by those voltammograms (Figure 3), it is knownthat equilibrium redox reaction of the polymerization isaccurate when potential scanning is run under a potentialrange of -0.9-1.0 V. Under this potential range, theresulting polypyrrole membrane has possible betterelectrical conductivity than that of under other potentialranges. The cyclic voltammogram is shown in Figure 2

also describes that the overoxidation possibility isinaccurate when potential scanning of pyrroleelectropolymerization is run under the potential range of-0.9-1.0 V.

The pyrrole

Figure 1. The general mechanism for the propagation of electrochemically polypyrrole formation.

Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 171

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Figure 2.Cyclic voltammograms of 0.01M pyrrole electropolymerization in aqueous solution containing 0.01M NaC104.Potential scanning runs on various potential ranges with an electric current of 2 mA and a scanning rate of 100 mV/s for

ten cycles. The direction of the right and down arrows indicate the scanning direction, while the direction of the uparrow indicates the current shifts from the first running of potential scanning.

Qi potential scanning of 0.1V and more causes a shift and anincrease in the anodic and cathodic peak currents, so thepotential scanning under a range of -0.8-1.1 V, -0.9-1.2V, dan -0.9-1.3 V produced new cathodic peak currentsand imperfect polypyrrole membrane structure. The newcathodic peaks current indicates that other reductionsfrom another species are occurring.

Overoxidation in pyrrole electropolymerizationtends to be accurate by an irreversible redox reaction, asshown in Figure 4 [29]. The conjugation system ofpolypyrrole is disrupted by a decrease in conductivity andrechargeability loss of the polymer.

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Figure 3. Cyclic voltammograms ofelectropolymerization of 0.01M pyrrole in an aqueous

solution containing 0.01M NaC104. The potentialscanning is carried out under a potential range of -0.9-1.0 V, an electric current of 2 mA, and a scanning rate of

100 mV/s for ten cycles. The right and down directions ofthe arrow show a scanning direction , while the directionof the up arrow indicates the current shifts from the first

running of potential scanning.

a.

Figure 4. Overoxidation mechanism of polypyrrole

The potential of over reduction and overoxidationdoes not appear at potential scanning run above -0.5 V(Figure 1). This fact is emphasized by the previous reportshowing that the potential of over reduction andoveroxidation appears on potential scans that run below-0.5 V only [30]. This phenomenon occurs only whenpyrrole electropolymerization is carried out in acidic orbasic solution due to the water oxidation reaction [28].Under the acidic and basic conditions, water moleculesare oxidized at -1.068 V and -0.191 V, respectively,concerning Ag/AgCl reference electrode [31].

The potential increase from -0.9 V to -0.5 V is notinfluenced by the high of anodic and cathodic currents butis influenced to reduce the range of potential scanningneeded. With the application, the scanning rate isconstant, decreasing the range of potential scanning thatis influenced by the electropolymerization time, and theninfluencing the perfection of the polymer formed.Conversely, an increase in the reverse directions of

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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 172

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Figure 5. Cyclic voltammograms of electropolymerization of 0.01M pyrrole in an aqueous solution containing 0.01MNaC104. The potential scanning is run under a potential range of -0.9-1.0 V, an electric current of 2 mA, and a scanning

rate of 50 mV/s (1), 80 mV/s (2), and 100 mV/s for ten cycles. Right and down directions of arrow show a scanningdirection, while up the arrow direction showed currents shift from the first running of potential scanning.

As reported by previous studies [27, 32, 33], theseobservations reveal the optimal scanning potential rangefor the pyrrole electropolymerization process in aqueoussolution by cyclic voltammetry is -0.9-1.0 V. In thispotential range, overoxidation and overreduction ofpyrrole electropolymerization did not occur [29]. Pyrroleelectropolymerization by scanning rate of 50, 80, and100

mV/s obtained cyclic voltammograms are shown inFigure 5. All cyclic voltammograms exhibit thatoveroxidation and overreduction are not involved in theelectropolymerization.

Pyrrole electropolymerization by scanning rate of 50mV/s and 80 mV/s produces similar cyclicvoltammograms, while the electropolymerization byscanning rate of 100 mV/s produces higher oxidation andreduction peak currents than its monomer and thepolymer (Table1).

electropolymerization needs a more extended time.Under the slow process of electropolymerization, a part ofpreviously formed cationic radicals reacts with watersolvent before reacting with monomer molecules so thatthe existence of reaction phenomena shown in Figure 4 isestablished.

On the other hand , pyrrole electropolymerizationwith a scanning rate of more than 100 mV/s produces toomany cationic radicals so that the irreversible formationreaction of the polymer is accurate and imperfectpolymers are formed. There is not enough time forcationic radicals to develop a chain reaction to form aperfect polymer under a too rapid scanning rate ofelectropolymerization processes. It is a consequence ofthe site reaction of cationic radicals with water molecules,as shown in Figure 6 [10].

Table 1. Typical parameters of pyrroleelectropolymerization based on scanning rate

Peak Current (i) Peak Potential (£)ScanningRate

(mV/s)Anodic, cathodic, Anodic, cathodic

( A) ( A) (V) (V)

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50 -0.21.1

80 -1.4 -0.21.1Figure 6. The secondary reaction of pyrrole

electropolymerization in an aqueous solution containingC104 supporting electrolyte.

1.6 -1.8 -0.5100

Pyrrole electropolymerization by lower scanningrate than 100 mV/s proceeds slowly so that the

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Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 173

The reaction of polypyrrole cations with watermolecules, as shown above, is accurate under thepotential range where those radicals are oxidized morereadily than their monomers. This reaction causes ahigher reduction peak current of the polymer than theoxidation peak current. Running the potential by too highscanning rate during pyrrole electropolymerization alsocauses an over dimerization reaction , followed byreleasing H+ ions into the solution so that the solution’sacidity increases. Under acidic solution , water moleculeswill be oxidized to form oxygen molecules so that thesecond reaction is accurate, as shown in Figure 7 [28].

The occurrence of the electropolymerization provesthe role of SDS as a supporting electrolyte.Electropolymerization of conducting polymer would notbe conducted in the absence of supporting electrolyte [19,35]. The addition of supporting electrolytes is primarilyintended to present the current of migration, whichinhibit the required diffusion currents [23]. The cyclicvoltammogram also shows that the SDS surfactantincreases the solution conductivity.

Pyrrole electropolymerization involves theformation mechanism of polypyrrole cation (PPy+ ). Theexistence of DS anion from SDSsurfactant in the aqueouspyrrole solution during electropolymerization processesis influenced by the polypyrrole formation reaction bythree possible phenomena: (1) Electrostatic interactionbetween DS anionsand polypyrrole cations; (2) Trappingthe hydrophobic chain of DS anions in the matrix of thepolymer formed (3) Micelle formation of surfactantinfluences the distribution of DS anions in the micelleand aqueous phases.

r\r\

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Figure 7. The secondary reaction of polymerization ofpyrrole in the water containing A supporting electrolyte

under acidic condition.The different roles of SDS and NaC104 as supporting

electrolytes are related to their molecular structures.TheSDS molecules have a long chain hydrophobic tail thatcauses mobility in the observed solution to be too slowthan NaCIO

Previous research has shown that the optimumscanning rate of pyrrole electropolymerization usingcyclic voltammetry technique is 100 mV/s. The pyrroleelectropolymerization process under a scanning rate ofmore than 100 mV/s will produce an imperfect polymer[34b

3.2. Pyrrole electropolymerization in the SDS solution

The cyclic voltammogram of pyrroleelectropolymerization in the aqueous SDS solution isshown in Figure 8. One oxidation peak current appears onthe voltammogram at 0.4 V, and three reduction peakcurrents appear at 0.7 V, 0.1V, and 0.3 V.

Cyclic voltammograms of pyrroleelectropolymerization in the existence of thosesupporting electrolytes describe the differences (Figures3and 8).

4*

3.3. Potential response of electrode to DS anions

Polypyrrole coated gold-wire electrode obtainedfrom the electrochemical process by cyclic voltammetrytechnique is then observed its possible compatibility asSDS surfactant sensor electrode (abbreviated as Au-PPy-DS). By this observation , the potential of polypyrrolemembranes as a mediator membrane candidate for theconstruction of the SDS surfactant sensor electrode isproven and can be intensively developed and furtherobserved.2.5 -

2.0-The electrode potential response can be explained

based on the interface equilibrium exchange of DS anionsdeveloped during SDS measurements [35, 36]. When theelectrode is dipped in the aqueous SDS solution, the shiftof the DS anions and the ion concentration gradientaround the electrodesurface causes the shift of DS anionsin the polypyrrole membrane to reach equilibriumbetween the membrane interface and aqueous analytesolution. This equilibrium is developed by the chemicalequation as follow:

PPy + DS

The potential response (E) of the electrodes resultingfrom the above reaction is derived by following Nernstequation:

1.5

3 0.5 -

C. C -- C .5-

-1.0-1.5

-1.2 -0.9 -0.6 -0.3 0.0 0.3 0.6 0.9 1.2E(mV)

PPy+ DS + eFigure 8. Cyclic voltammogram of electropolymerizationof 0.01M pyrrole in an aqueous solution containing 0.01M SDS.The potential scanning is run under a potentialrange of -0.9-1.0 V, an electric current of 2 mA, and a

scanning rate of 100 mV/s for five cycles. Right and downdirections of arrow show a scanning direction, while upthe arrow direction showed currents shift from the first

running of potential scanning.

E = E° + (RT/ nF) In

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−

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−

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mV/decade 9.9slope =

Jurnal Kimia Sains dan Aplikasi 23 (5) (2020):167-176 174

where a0and arare oxidized (PPy+ ) activitiesand reduced(PPy) forms of polypyrrole membrane, respectively,while CIDS are the DS anion activity in the aqueoussolution. Because the membrane doping level is constant ,then the equation above can be simply written as:

E = E°-( RT/ nF ) In aDS

The sensitivity value is not the only parameter ofelectrode capability, but it is the first substantialinformation for evaluating the electrode’s potentialbehavioral response. The electrode’s sensitivity is still farfrom the Nerstian value for a single-charged analyte (59mV/decade). Nevertheless, as a preliminary study, thisvalue is a good indication for the observed electrode to bedeveloped in future studies.

To increase electrodes’ sensitivity, studies todetermine the optimal solution composition of theelectropolymerization, such as pyrrole concentration,type and concentration of supporting electrolyte, and thecontent of DS ionophore are needed. The study of cyclicvoltammetry parameters is developed to obtain theoptimal thickness of the membrane if the polymermembrane thickness also influences the electrode’ssensitivity.

While the main potentiometric parameters that willbe further observed are the Nerstian sensitivity ofelectrode, the range of measurement concentrations orcalibration curve, and the limit of detection, thoseparameters are determined by plotting the potentialresponse of the electrode as a function of theconcentration of analyte SDS solution. The sensitivity ofthe electrode is determined from the slope of thecalibration curve, while the limit of detection isdetermined from the lowest value of DS concentration inthe extrapolated line of the calibration curve.

4. ConclusionElectrocoating polypyrrole at the surface of the gold-

wire electrode can be conducted directly by cyclicvoltammetry technique in the electrochemical cellcontaining pyrrole with the existence of supportingelectrolyte species. The chemical and physicalcharacteristics of the polypyrrole membrane depend onparameters of cyclic voltammetry applied, such as thepotential range of scanning, scanning rate, and theexistence of supporting electrolytes. DS anion dopantsare trapped directly in the polypyrrole membrane matrixduring the electropolymerization process in theelectrochemical cell containing supporting electrolyte ofinorganic salts. The DS dopant trapped in the polymerroles as ionophore to recognize DS anions in the SDSsurfactant of analyte solution. DS anion itself also actsasa supporting electrolyte in electrochemical cells withoutsupporting electrolyte of inorganic salts. Polypyrrolecoated on the surface of the gold-wire electrodes isproved applicable as a potential mediator membrane forthe electric conductor and ion exchanger during themeasurement of DS anions in an aqueous samplesolution.

= E°-(2,303 RT/ nF ) log aDS

The last equation informs that the electrode’spotential is straightly proportional to the activity orconcentration of DS analyte, and therefore, the electrodeis applicable to determine SDS surfactantpotentiometrically. The 2,303 RT/ nF value is referred to asthe sensitivity of electrode in the unit of mV/decade.

As shown in Figure 9, the Au-PPy-DS electrodeobtained in this observation is proved to be able torespond to the DS anions from analyte solution in theconcentration range of 10 7-io 5 M, with the sensitivity ofelectrode of 9.9 mV/decade and limit of detection of 10 7

M.

The electrode capability to respond to DS anionsdescribes that a small part of the SDS molecule is trappedin the matrix of polypyrrole membrane during pyrroleelectropolymerization. These DS anions then acts as adopant ionophore in the potentiometric measurement oftheDS analyte by Au-PPy-DS.

The electrode sensitivity value is still too low than theNerstian value (59 mV/decade). However , the electrodes’ability to detect DS anion analytes provide a goodindication that the polypyrrole membrane is coated onthe surface of the gold wire electrodes produced from thisexperiment, enabling the DS-anion exchangemechanism. So, this type of electrode can be furtherdesigned to be an elective-selective ion (ISE) for thedetermination of SDS surfactants with innovativeresearch parameters.

450

425

>E 400LU

375

350

0 1 2 3 4 5 6 7 8 9 1 0

pNaDS

Figure 9. Potential response of the Au-PPy-DS electrode.Preparation of the electrode was performed by cyclicvoltammetry technique under a potential range of

running of -0.9-1.0 V, the scanning rate of 100 mV/s,and electric current of 2 mA for 60 cycles.

Electropolymerization was performed in theelectrochemical cell containing the mixture solution of0.05 M pyrrole and 0.001M SDS. The sensitivity of the

electrode to DS anion was 9.9 mV/decade.

AcknowledgmentThe authors thank the research laboratory of the

Department of Chemistry, Faculty of Mathematics and

Jurnal Kimia Sains dan Aplikasi 23 (5) (2020): 167-176 175

Natural Sciences, Halu Oleo University for supportingfacility.

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