NANO EXPRESS Open Access [623916]

NANO EXPRESS Open Access
Silver-functionalized carbon nanofiber composite
electrodes for ibuprofen detection
Florica Manea1*, Sorina Motoc1, Aniela Pop1, Adriana Remes1and Joop Schoonman2
Abstract
The 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 composite
electrodes suitable for ibuprofen detection in aqueous solution. Ag carbon nanotube composite electrodeexhibited the best electroanalytical parameters through applying preconcentration/differential-pulsed voltammetry
scheme.
Keywords: Carbon nanofiber composite electrodes, Silver particles, Electrochemical determination, Ibuprofen
Background
Nanoscale carbonaceous materials, especially carbon
nanotubes (CNTs) and carbon nanofibers (CNFs), have
attracted great research interests in the electroanalysis
field. The development of carbon nanofiber-based com-posite electrodes combine the enhanced electrical proper-
ties and ease of processing of such electrodes exhibiting
attractive electrochemical and economical features [1,2].However, the improvement of the electroanalytical signal
requires 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 as
emerging pollutants. Ibuprofen (IBP) is the third mostpopular drug in the world, and its presence in water
requires 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, there
is no information about ibuprofen detection using ananostructured carbon-based electrode. In this paper, two
types 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.Methods
CNFs with diameters of 60 to 150 nm and lengths of30 to 100 μm were purchased from Applied Sciences
Inc., Cedarville, Ohio (Pyrograf III – PR24 AGLD).
Silver-modified zeolite was prepared by ion-exchangeusing natural zeolite (NZ) from Mirsid, Romania (68
wt.%) as we previously described [8]. Araldite
WLY5052/
AradurW5052 two-component epoxy resin used in the
study was purchased from Huntsman Advanced Mate-
rials, Basel, Switzerland. The decoration of the CNF
composite 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 mL
of DMF, and the mixture was subjected to ultrasonica-tion (Cole-Parmer 8900, Vernon Hills, Chicago, IL,
USA) for 1 h; 40 mL of an AgNO
3solution (0.02 M)
was added into the mixture with the temperature of60°C to 62°C during the stirring. After 1 h, heating
the solution was kept without stirring at room
temperature for 48 h for Ag deposition, and after fil-tration and subsequently washing with water, ethanol,
and acetone, silver-decorated CNF was obtained. The
composite electrodes were prepared by dispersion ofCNFs in DMF, 99.9% (DMF, Sigma-Aldrich, Corporation,
St. Louis, MO, USA) and epoxy resin (Araldite
WLY5052)
by ultrasonication, followed by the homogenizationof the resulting paste with the zeolite particles and
also with the hardener using a two-roll mill. The
mixture was then poured into PVC tubes and curedat 60°C for 24 h obtaining disc electrodes with a
* Correspondence: florica.manea@chim.upt.ro
1Politehnica ”University of Timisoara, Timisoara 300006, Romania
Full list of author information is available at the end of the article
© 2012 Manea et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproductionin any medium, provided the original work is properly cited.Manea et al. Nanoscale Research Letters 2012, 7:331
http://www.nanoscalereslett.com/content/7/1/331

surface area of 0.196 cm2. The ratios were chosen to
obtain 20 wt.% CNFs for the AgCNF electrode and
also 20 wt.% Ag-modified zeolite for the AgZCNFelectrode. Scanning elec tron microscopy coupled
with energy dispersive X-ray analysis detection
(SEM/EDX) was performed using an Inspect SPANalytical instrument (PANalytical B.V., Almelo,
The Netherlands). Electrochemical measurements
were 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 composit e electrodes for IBP de-
t e c t i o ni nt h ea q u e o u ss o l u t i o n .Results and discussion
Surface characterization
Figure 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 the
epoxy matrix is observed. Higher content of Ag particleswas found for silver-modified natural zeolite-CNF-epoxy
in comparison with silver-decorated CNF-epoxy com-
posite materials.
Cyclic voltammetric measurements
Figure 2a,b shows the series of the cyclic voltammo-
grams recorded at AgCNF and AgZCNF composite elec-
trodes in 0.1 M Na 2SO4supporting electrolyte and in
the presence of various IBP concentrations. Similar
shapes of the voltammograms can be noticed for both
electrodes, and the oxidation peak corresponding to theAg/Ag
+couple appeared at the potential value of +0.3
a b
Figure 1 SEM/EDX images of (a) AgCNF and (b) AgZCNF electrode materials.
ab
Figure 2 Recorded cyclic voltammograms. These were recorded at ( a) AgCNF, ( b) AgZCNF electrodes in 0.1 M Na 2SO4supporting electrolyte
(curve 1) and in the presence of various IBP concentrations that consists 1 to 8 mg L−1(curves 2 to 9); potential scan rate of 50 mV s−1. Inset:
calibration plots of peak current vs. IBP concentration.Manea et al. Nanoscale Research Letters 2012, 7:331 Page 2 of 4
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V/SCE, which is more evidenced for AgZCNF in direct
relation with the silver content. The current correspond-
ing to the IBP oxidation peak recorded at about +1.3 V
vs. Ag/AgCl increased progressively with its concentra-tion (see insets of Figure 2). On the following reverse
scan from 1.5 to −0.5 V vs. Ag/AgCl, no corresponding
reduction peak is observed, revealing that the electrodeprocess at both electrodes is totally irreversible.
Electrochemical detection of ibuprofen
The simplest electroanalytical procedure should involve
the recording of the chronoamperogram, based on the
reference provided by the cyclic voltammograms. Thus,for both electrodes, the continuous chronoamperograms
were 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 for
AgCNF, while for AgZCNF, a lower sensitivity was
achieved probably due to electrode fouling that occurredunder these working conditions (see Table 1).In order to improve the electroanalytical performances
of both electrodes for IBP detection, the DPV technique
was applied after optimization of its parameters.
Figure 3a,b presents DPVs recorded at both electrodes,and the sensitivity was improved only for the AgZCNF
composite electrode. This aspect can be explained by the
higher value of the background current for AgZCNF incomparison with AgCNF, which indicated a smaller
amount 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 detection
scheme was tested after the optimum accumulation timesettling based on the results of the effect of accumulation
time on the currents of the differential-pulse anodic peak
recorded at +1.15 V vs. Ag/AgCl corresponding to IBPoxidation. The accumulation time is considered the time
maintaining at open-circuit potential before running the
DPV. The enhancement factor was determined as ratio ofthe peak current recorded at different accumulation timesTable 1 Electroanalytical performances of AgCNF and AgZCNF composite electrodes for IBP detection in 0.1-M Na 2SO4
supporting electrolyte
Used 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 0.03
AgCNF +1.3 1.400 0.996 1 to 8 3.20 0.02
DPV AgZCNF +1.17 2.867 0.993 0.5 to 5 3.75 0.008
AgCNF +1.15 1.810 0.977 0.5 to 5 3.90 0.01
Preconcentration/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 0.009
AgCNF +1.2 2.140 0.992 0.5 to 5 3.80 0.008
CA AgZCNF +1.3 0.317 0.975 0.5 to 4.5 1.40 0.03
AgCNF +1.3 1.636 0.944 0.5 to 4.5 1.25 0.02
E/V, detection potential/Volt vs. Ag/AgCl; LOD, lowest limit of detection; RSD, relative standard deviation; SWV, square-wave voltammetry.
ab
Figure 3 Recorded differential-pulsed voltammograms (0.2 V modulation amplitude, 0.02 V step potential). They were recorded at ( a)
AgCNF, ( b) AgZCNF electrodes in 0.1 M Na 2SO4supporting electrolyte and in the presence of various IBP concentrations that consists 0.5 to 5
mg /C1L−1(curves 2 to 11). Inset: calibration plots of the anodic current recorded at E = +1.15 V vs. IBP concentration.Manea et al. Nanoscale Research Letters 2012, 7:331 Page 3 of 4
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to that recorded without a preconcentration scheme, and
the maximum value of about 4 was reached for AgCNF
and 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 IBP
detection was improved; a value of 4.15 μA/mg L
−1was
achieved in comparison with 1.81 μA/mg L−1without
preconcentration.
Conclusions
AgCNF and AgZCNF composite electrodes were suc-
cessfully prepared by a two-roll mill procedure. SEM
images showed the presence of silver particles and agood dispersion of CNF into the epoxy matrix. Both
electrodes exhibited good sensitivities for ibuprofen de-
termination using CV, DPV, and CA techniques. More-over, using CA as the simplest electrochemical technique
with real practical potential, a very good electroanalytical
performance for IBP detection at 1.3 V vs. Ag/AgCl wasreached using the AgCNF electrode. Also, the AgCNF
composite electrode exhibited useful properties for apply-
ing the preconcentration-voltammetric detection tech-nique, which allowed the achievement of a better
sensitivity 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.
Abbreviations
AgCNF: Silver-decorated CNF-epoxy electrode; AgZCNF: Silver-modifiednatural zeolite-CNF-epoxy electrode; CA: Chronoamperometry; CNF: Carbon
nanofibers; CNT: Carbon nanotubes; CV: Cyclic voltammetry; DMF: N,N-
dimethylformamide; DPV: Differential-pulsed voltammetry; IBP: Ibuprofen;NZ: Natural zeolite; SEM: Scanning electron microscopy.
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
FM conceived and coordinated the study, and carried out the electrode
preparation and data interpretation. SM carried out the electrochemical
detection 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' information
FM 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.
Acknowledgments
This 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 European
Social Fund – Investing in People, within the Sectoral Operational
Programme Human Resources Development 2007 to 2013 and partially bythe PN-II- ID-PCE-165/2011 and PNII-RU-PD129/2010 grants.Author details
1Politehnica ”University of Timisoara, Timisoara 300006, Romania.
2Department ChemE, Delft University of Technology, Delft 2600 AA, The
Netherlands.
Received: 10 January 2012 Accepted: 17 April 2012
Published: 21 June 2012
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doi:10.1186/1556-276X-7-331
Cite this article as: Manea et al. :Silver-functionalized carbon nanofiber
composite electrodes for ibuprofen detection. Nanoscale Research Letters
2012 7:331.
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