Adriana Remes

Aniela Pop

C Orha

F Marken

F Xin

Florica Manea

Joop Schoonman

L Rassaei

MR Khoshayand

MR Whelan

S Motoc

Sorina Motoc

WS Hassan

Nanoscale Research Letters

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Manea et al. Nanoscale Research Letters 2012, 7:331http://www.nanoscalereslett.com/content/7/1/331NANO EXPRESS Open AccessSilver-functionalized carbon nanofiber compositeelectrodes for ibuprofen detectionFlorica Manea1*, Sorina Motoc1, Aniela Pop1, Adriana Remes1 and Joop Schoonman2AbstractThe aim of this study is to prepare and characterize two types of silver-functionalized carbon nanofiber (CNF)composite electrodes, i.e., silver-decorated CNF-epoxy and silver-modified natural zeolite-CNF-epoxy compositeelectrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrodeexhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetryscheme.Keywords: Carbon nanofiber composite electrodes, Silver particles, Electrochemical determination, IbuprofenBackgroundNanoscale carbonaceous materials, especially carbonnanotubes (CNTs) and carbon nanofibers (CNFs), haveattracted great research interests in the electroanalysisfield. The development of carbon nanofiber-based com-posite electrodes combine the enhanced electrical proper-ties and ease of processing of such electrodes exhibitingattractive electrochemical and economical features [1,2].However, the improvement of the electroanalytical signalrequires catalyst incorporation into the composite matrix,and silver-decorated CNT has been reported [3]. In recentyears, there has been increasing concern about the pres-ence of pharmaceutical compounds in water, known asemerging pollutants. Ibuprofen (IBP) is the third mostpopular drug in the world, and its presence in waterrequires viable methods for its determination. Several de-termination methods have been reported in the literaturee.g., spectrophotometry [4,5], HPLC [6], and an electro-chemical method [7]. To the best of our knowledge, thereis no information about ibuprofen detection using ananostructured carbon-based electrode. In this paper, twotypes of silver-functionalized CNF composite electrodes,silver-decorated CNF-epoxy (AgCNF) and silver-modifiednatural zeolite-CNF-epoxy (AgZCNF) composite electro-des were prepared, morphologically characterized, and ap-plied for IBP detection in aqueous solution.* Correspondence: florica.manea@chim.upt.ro1Politehnica” University of Timisoara, Timisoara 300006, RomaniaFull list of author information is available at the end of the article© 2012 Manea et al.; licensee Springer. This is aAttribution License (http://creativecommons.orin any medium, provided the original work is pMethodsCNFs with diameters of 60 to 150 nm and lengths of30 to 100 μm were purchased from Applied SciencesInc., Cedarville, Ohio (Pyrograf III - PR24 AGLD).Silver-modified zeolite was prepared by ion-exchangeusing natural zeolite (NZ) from Mirsid, Romania (68wt.%) as we previously described [8]. AralditeWLY5052/AradurW5052 two-component epoxy resin used in thestudy was purchased from Huntsman Advanced Mate-rials, Basel, Switzerland. The decoration of the CNFcomposite with silver nanoparticles was carried out byreducing silver ions in the presence of N,N-dimethyl-formamide (DMF). A 1.1-g CNF was added to 550 mLof DMF, and the mixture was subjected to ultrasonica-tion (Cole-Parmer 8900, Vernon Hills, Chicago, IL,USA) for 1 h; 40 mL of an AgNO3 solution (0.02 M)was added into the mixture with the temperature of60°C to 62°C during the stirring. After 1 h, heatingthe solution was kept without stirring at roomtemperature for 48 h for Ag deposition, and after fil-tration and subsequently washing with water, ethanol,and acetone, silver-decorated CNF was obtained. Thecomposite electrodes were prepared by dispersion ofCNFs in DMF, 99.9% (DMF, Sigma-Aldrich, Corporation,St. Louis, MO, USA) and epoxy resin (AralditeWLY5052)by ultrasonication, followed by the homogenizationof the resulting paste with the zeolite particles andalso with the hardener using a two-roll mill. Themixture was then poured into PVC tubes and curedat 60°C for 24 h obtaining disc electrodes with an Open Access article distributed under the terms of the Creative Commonsg/licenses/by/2.0), which permits unrestricted use, distribution, and reproductionroperly cited.a bFigure 1 SEM/EDX images of (a) AgCNF and (b) AgZCNF electrode materials.Manea et al. Nanoscale Research Letters 2012, 7:331 Page 2 of 4http://www.nanoscalereslett.com/content/7/1/331surface area of 0.196 cm2. The ratios were chosen toobtain 20 wt.% CNFs for the AgCNF electrode andalso 20 wt.% Ag-modified zeolite for the AgZCNFelectrode. Scanning electron microscopy coupledwith energy dispersive X-ray analysis detection(SEM/EDX) was performed using an Inspect SPANalytical instrument (PANalytical B.V., Almelo,The Netherlands). Electrochemical measurementswere carried out using an Autolab PGSTAT101(Metrohm Autolab, Utrecht, The Netherlands) con-trolled with the NOVA 1.6 software and a three-electrode cell with an Ag/AgCl reference electrode, aplatinum counter electrode, and the composite work-ing electrodes. Cyclic voltammetry (CV), differential-pulsed voltammetry (DPV), and chronoamperometry(CA) were used to assess the electroanalytical per-formance of both composite electrodes for IBP de-tection in the aqueous solution.aFigure 2 Recorded cyclic voltammograms. These were recorded at (a) A(curve 1) and in the presence of various IBP concentrations that consists 1calibration plots of peak current vs. IBP concentration.Results and discussionSurface characterizationFigure 1a,b presents the SEM/EDX images of both elec-trodes, i.e., AgCNF and AgZCNF composite electrodes,and a homogeneous distribution of CNF within theepoxy matrix is observed. Higher content of Ag particleswas found for silver-modified natural zeolite-CNF-epoxyin comparison with silver-decorated CNF-epoxy com-posite materials.Cyclic voltammetric measurementsFigure 2a,b shows the series of the cyclic voltammo-grams recorded at AgCNF and AgZCNF composite elec-trodes in 0.1 M Na2SO4 supporting electrolyte and inthe presence of various IBP concentrations. Similarshapes of the voltammograms can be noticed for bothelectrodes, and the oxidation peak corresponding to theAg/Ag + couple appeared at the potential value of +0.3bgCNF, (b) AgZCNF electrodes in 0.1 M Na2SO4 supporting electrolyteto 8 mg L−1 (curves 2 to 9); potential scan rate of 50 mV s−1. Inset:Table 1 Electroanalytical performances of AgCNF and AgZCNF composite electrodes for IBP detection in 0.1-M Na2SO4supporting electrolyteUsed technique Electrode material E/V Electrode sensitivity(μA/mg L−1)Correlation coefficient(R2)Concentration range(mg L−1)RSD(%) LOD(mg L-1)CV AgZCNF +1.29 1.846 0.998 1 to 8 3.50 0.03AgCNF +1.3 1.400 0.996 1 to 8 3.20 0.02DPV AgZCNF +1.17 2.867 0.993 0.5 to 5 3.75 0.008AgCNF +1.15 1.810 0.977 0.5 to 5 3.90 0.01Preconcentration/DPV AgCNF +1 4.150 0.998 0.5 to 5 4.25 0.001SWV AgZCNF +1.25 2.27 0.988 0.5 to 5 4.20 0.009AgCNF +1.2 2.140 0.992 0.5 to 5 3.80 0.008CA AgZCNF +1.3 0.317 0.975 0.5 to 4.5 1.40 0.03AgCNF +1.3 1.636 0.944 0.5 to 4.5 1.25 0.02E/V, detection potential/Volt vs. Ag/AgCl; LOD, lowest limit of detection; RSD, relative standard deviation; SWV, square-wave voltammetry.Manea et al. Nanoscale Research Letters 2012, 7:331 Page 3 of 4http://www.nanoscalereslett.com/content/7/1/331V/SCE, which is more evidenced for AgZCNF in directrelation with the silver content. The current correspond-ing to the IBP oxidation peak recorded at about +1.3 Vvs. Ag/AgCl increased progressively with its concentra-tion (see insets of Figure 2). On the following reversescan from 1.5 to −0.5 V vs. Ag/AgCl, no correspondingreduction peak is observed, revealing that the electrodeprocess at both electrodes is totally irreversible.Electrochemical detection of ibuprofenThe simplest electroanalytical procedure should involvethe recording of the chronoamperogram, based on thereference provided by the cyclic voltammograms. Thus,for both electrodes, the continuous chronoamperogramswere recorded at the potential value of + 1.3 V vs. Ag/AgCl within the IBP concentration range between 0.5and 5 mg L−1. The sensitivity was compared to CV forAgCNF, while for AgZCNF, a lower sensitivity wasachieved probably due to electrode fouling that occurredunder these working conditions (see Table 1).aFigure 3 Recorded differential-pulsed voltammograms (0.2 V modulaAgCNF, (b) AgZCNF electrodes in 0.1 M Na2SO4 supporting electrolyte andmgL−1 (curves 2 to 11). Inset: calibration plots of the anodic current recordIn order to improve the electroanalytical performancesof both electrodes for IBP detection, the DPV techniquewas applied after optimization of its parameters.Figure 3a,b presents DPVs recorded at both electrodes,and the sensitivity was improved only for the AgZCNFcomposite electrode. This aspect can be explained by thehigher value of the background current for AgZCNF incomparison with AgCNF, which indicated a smalleramount of silver particles in AgCNF which is in accord-ing with the SEM/EDX results.To explore the sorption capacity of both electrodes to-wards IBP, a preconcentration-voltammetric detectionscheme was tested after the optimum accumulation timesettling based on the results of the effect of accumulationtime on the currents of the differential-pulse anodic peakrecorded at +1.15 V vs. Ag/AgCl corresponding to IBPoxidation. The accumulation time is considered the timemaintaining at open-circuit potential before running theDPV. The enhancement factor was determined as ratio ofthe peak current recorded at different accumulation timesbtion amplitude, 0.02 V step potential). They were recorded at (a)in the presence of various IBP concentrations that consists 0.5 to 5ed at E = +1.15 V vs. IBP concentration.Manea et al. Nanoscale Research Letters 2012, 7:331 Page 4 of 4http://www.nanoscalereslett.com/content/7/1/331to that recorded without a preconcentration scheme, andthe maximum value of about 4 was reached for AgCNFand about 2 for AgZCNF at the accumulation time of 20min. At longer accumulation times, no higher current re-sponse was obtained (the results are not shown here). Ap-plying the preconcentration-voltammetric detectionscheme using the AgCNF electrode, the sensitivity for IBPdetection was improved; a value of 4.15 μA/mg L−1 wasachieved in comparison with 1.81 μA/mg L−1 withoutpreconcentration.ConclusionsAgCNF and AgZCNF composite electrodes were suc-cessfully prepared by a two-roll mill procedure. SEMimages showed the presence of silver particles and agood dispersion of CNF into the epoxy matrix. Bothelectrodes exhibited good sensitivities for ibuprofen de-termination using CV, DPV, and CA techniques. More-over, using CA as the simplest electrochemical techniquewith real practical potential, a very good electroanalyticalperformance for IBP detection at 1.3 V vs. Ag/AgCl wasreached using the AgCNF electrode. Also, the AgCNFcomposite electrode exhibited useful properties for apply-ing the preconcentration-voltammetric detection tech-nique, which allowed the achievement of a bettersensitivity without electrode fouling occurring. In com-parison with our previous reported work [7], better resultswere achieved in this study for the lowest limit of detec-tion of ibuprofen in the aqueous solution.AbbreviationsAgCNF: Silver-decorated CNF-epoxy electrode; AgZCNF: Silver-modifiednatural zeolite-CNF-epoxy electrode; CA: Chronoamperometry; CNF: Carbonnanofibers; CNT: Carbon nanotubes; CV: Cyclic voltammetry; DMF: N,N-dimethylformamide; DPV: Differential-pulsed voltammetry; IBP: Ibuprofen;NZ: Natural zeolite; SEM: Scanning electron microscopy.Competing interestsThe authors declare that they have no competing interests.Authors' contributionsFM conceived and coordinated the study, and carried out the electrodepreparation and data interpretation. SM carried out the electrochemicaldetection measurements. AP and AR performed SEM measurements andcontributed to electrode preparation. JS participated in the design andcoordination. All authors read and approved the final manuscript.Authors' informationFM is an associate professor of Electrochemistry Applied for EnvironmentRemediation and Monitoring. AP is a postdoctoral research associate. JS is aprofessor of Advanced Materials. SM and AR are Ph.D. students.AcknowledgmentsThis work was partially supported by the strategic grants POSDRU/89/1.5/S/57649, Project ID 57649 (PERFORM-ERA), POSDRU/89/1.5/S/63700 andPOSDRU/88/1.5/S/50783, Project ID 50783 and co-financed by the EuropeanSocial Fund - Investing in People, within the Sectoral OperationalProgramme Human Resources Development 2007 to 2013 and partially bythe PN-II- ID-PCE-165/2011 and PNII-RU-PD129/2010 grants.Author details1Politehnica” University of Timisoara, Timisoara 300006, Romania.2Department ChemE, Delft University of Technology, Delft 2600 AA, TheNetherlands.Received: 10 January 2012 Accepted: 17 April 2012Published: 21 June 2012References1. Rassaei L, Sillanpaa M, Bonne MJ, Marken F: Carbon nanofiber-polystyrenecomposite electrodes for electroanalytical processes. Electroanalysis 2007,19:1461–1466.2. Marken F, Gerrard ML, Mellor IM, Mortimer RJ, Madden CE, Fletcher S, HoltK, Foord JS, Dahm F: Voltammetry at carbon nanofiber electrodes.Electrochemistry Communication 2001, 3:177–180.3. Xin F, Li L: Decoration of carbon nanotubes with silver nanoparticles foradvanced CNT/polymer nanocomposites. Composites: Part A 2011,42:961–967.4. Hassan WS: Determination of ibuprofen and paracetamol in binarymixture using chemometric-assisted spectrophotometric methods. Am JAppl Sci 2008, 5:1005–1012.5. Khoshayand MR, Abdollahi H, Shariatpanahi M, Saadatfard A, Mohammadi A:Simultaneous spectrophotometric determination of paracetamol,ibuprofen and caffeine in pharmaceuticals by chemometric methods.Spectrochimica Acta A 2008, 70:491–499.6. Whelan MR, Ford JL, Powell MW: Simultaneous determination ofibuprofen and hydroxypropylmethylcellulose (HPMC) using HPLC andevaporative light scattering detection. J Pharm Biomed Anal 2002,30:1355–1359.7. Motoc S, Manea F, Pop A, Pode R, Burtica G: Determination of ibuprofen inwater using Ag-doped zeolite-expanded graphite composite electrode.J Sci Conf Proc 2011, 3:1–6.8. Orha C, Pop A, Lazau C, Grozescu I, Tiponut V, Manea F: Structuralcharacterization and the sorption properties of the natural and syntheticzeolite. J Optoelectron Adv Mater 2011, 13(5–6):544–549.doi:10.1186/1556-276X-7-331Cite this article as: Manea et al.: Silver-functionalized carbon nanofibercomposite electrodes for ibuprofen detection. Nanoscale Research Letters2012 7:331.Submit your manuscript to a journal and beneﬁ t from:7 Convenient online submission7 Rigorous peer review7 Immediate publication on acceptance7 Open access: articles freely available online7 High visibility within the ﬁ eld7 Retaining the copyright to your article    Submit your next manuscript at 7 springeropen.com

Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection

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Silver-functionalized carbon nanofiber composite electrodes for ibuprofen detection

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