Green synthesized silver nanoparticles decorated on reduced graphene oxide for enhanced electrochemical sensing of nitrobenzene in waste water samples

Article abstract of DOI:10.1039/c5ra00992h

In the present work, an electrochemical sensor for nitrobenzene (NB) has been developed based on a green synthesized silver nanoparticles (AgNPs) decorated reduced graphene oxide (RGO) modified glassy carbon electrode (GCE). The AgNPs were synthesized using Justicia glauca leaf extract as a reducing and stabilizing agent. A RGO-AgNPs composite modified electrode was prepared by a simple electrochemical reduction of AgNPs dispersed GO solution. FESEM of RGO-AgNPs composite confirms that AgNPs are firmly attached on the RGO sheets and the average size of AgNPs is found to be 40 ± 5 nm. The modified electrode shows good efficiency with lower overpotential for electrocatalytic reduction of NB than that of other modified electrodes (AgNPs and RGO). The DPV response confirms that the reduction peak current of NB is linear over the concentrations from 0.5 to 900 μM. The sensitivity of the sensors is found to be 0.836 μA μM^-1 cm^-2 with the detection limit of 0.261 μM for NB. In addition, the RGO-AgNPs composite modified electrode shows good selectivity in the presence of potentially interfering similar compounds and good practicality in the waste water samples. This journal is

Full text of DOI:10.1039/c5ra00992h

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Journal Name
RSCPublishing
ARTICLE
Green synthesized silver nanoparticles decorated on
reduced graphene oxide for enhanced electrochemical
sensing of nitrobenzene in waste water samples
Cite this: DOI: 10.1039/x0xx00000x
c
a
b
a, c*
K. Chelladurai,
K. Muthupandi,
S.M. Chen,
M. Ajmal Ali, P.
Received 00th January 2012,
Accepted 00th January 2012
P. Prakash, b** Fahad M. A. AlꢀHemaid, c BihꢀShow
a
b
Selvakumar, A. Rajan
,
DOI: 10.1039/x0xx00000x
www.rsc.org/
Loud
***
In the present work, an electrochemical sensor for nitrobenzene has been developed based on green
synthesized silver nanoparticles (AgNPs) decorated reduced graphene oxide (RGO) modified glassy
carbon electrode (GCE). The AgNPs were synthesized using Justicia glauca leaf extract as a reducing
and stabilizing agent. RGOꢀAgNPs composite modified electrode was prepared by a simple
electrochemical reduction of AgNPs dispersed GO solution. FESEM of RGOꢀAgNPs composite
confirms that AgNPs are firmly attached on the RGO sheets and the average size of AgNPs is found to
be 40 ± 5 nm. The modified electrode shows good efficiency with lower overpotential for electrocatalytic
reduction of NB than that of other modified electrodes (AgNPs and RGO). The DPV response confirms
that the reduction peak current of NB is linear over the concentrations from 0.5 to 900 µM. The
sensitivity of the sensors is found to be 0.836 µAµM–1 cm–2 with the detection limit of 0.261 µM for NB.
In addition, the RGOꢀAgNPs composite modified electrode shows good selectivity in the presence of
potentially interfering similar compounds and good practicality in the waste water samples.
toxicity of water bodies. It is very stable in aqueous solution due to
the presence of NO2 group.5–7 Therefore, the sensitive determination
1. Introduction
Nitrobenzene (NB) is a highly toxic carcinogenic compound and has
been listed as one of the priority pollutants by United States
Environmental Protection Agency (USEPA).1 It has also been used
as a raw material for the preparation of explosives, herbicides,
insecticides, aniline and dyes.2–4 Even in very low concentration, the
NB may pose great threat to human health and environment. Large
amount of NB is released from the industries and resulting in high
of NB in environmental samples is of great importance for human
health. The well known methods for NB determination are based on
chromatographic,
spectrophotometry
and
electrochemical
methods.8–10 In recent years, electrochemical methods are widely
used for the quantitative determination of NB due to their high
sensitivity, easy handling and low cost.11
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Compared to unmodified electrodes, the nanomaterials
Silver nitrate (AgNO3) and nitrobenzene were purchased
modified electrodes have been widely used for the electrochemical from Sigma–Aldrich. The leaves of Justicia glauca were collected
determination of NB owing to their high surface area and excellent from Sirumalai hills region, Tamil Nadu, India. Raw graphite with
electrochemical property.12 In addition, these modified electrodes average diameter about >20 µm was obtained from Sigma Aldrich.
enhance the sensitivity and selectivity of the NB detection more than The supporting electrolyte used for all experiments was prepared by
that of conventional electrodes. Researchers have paid much using 0.05 M Na2HPO4 and NaH2PO4 solutions. All other chemicals
attention on reduced graphene oxide (RGO) owing to its unique were of analytical grade and the solutions were prepared with
properties such as high specific surface area and high chemical doubleꢀdistilled water.
stability.13–15 The unique properties of RGO combined with other
Methods
nanomaterials have been used for different potential applications,
Cyclic voltammetry (CV) and differential pulse voltammetry
such as energy storage, antibacterial, electrochemical sensor and
(DPV) experiments were carried out using CHI 750a work station. A
biosensors, gas sensors etc.16–23 Among the variety of metal and
conventional threeꢀelectrode cell containing the modified GCE was
metal oxide nanoparticles, AgNPs have received considerable
used as a working electrode. Pt wire and saturated Ag/AgCl were
interest due to their unique structural properties including sensing of
used as a counter and reference electrodes, respectively. Surface
nitro compounds.24–27 Recently, our group has found that the green
morphological study was carried out using JSMꢀ6500F field
synthesized nanoparticles have high electrocatalytic activity towards
emission scanning electron microscope (FESEM) and the elemental
NB.27 However, the green synthesized AgNPs have some limitations
analysis was performed using Hitachi Sꢀ3000 H scanning electron
on the detection of nitro compounds, such as low sensitivity, lower
microscope attached with Energy Dispersive Xꢀray Analyzer. Jasco
response range and narrow potential window. In order to improve
Vꢀ560 doubleꢀbeam spectrophotometer was used for UV–visible
the sensitivity, the AgNPs have been combined with RGO and used
spectral analysis. All the electrochemical measurements were
for the ultrasensitive detection of NB.
carried out at room temperature in a nitrogen (N2) atmosphere.
Herein, we report the electrochemical determination of
Green synthesis of AgNPs
The 50 mL of Justicia glauca leaf extract was mixed with
NB using AgNPs decorated RGO (RGOꢀAgNPs) modified glassy
carbon electrode (RGO). The modified electrode exhibits good
sensitivity and lower overpotential compared to AgNPs and RGO
modified electrodes. Moreover, the analytical performance of the
modified electrode has been evaluated in waste water samples and
the selectivity of the fabricated sensor has also been determined in
the presence of potentially interfering compounds such as nitro and
phenolic compounds and metal ions.
100 mL of aqueous solution of 1 mM AgNO3 at room temperature.
The pale greenish yellow colour solution becomes deeper brown
within an hour and no noticeable difference in the colour of aqueous
silver colloids is observed, which indicates that the bioꢀreduction
process is over within an hour. The colour changes indicate the
formation of AgNPs in aqueous solution due to excitation of Surface
Plasmon vibration in the metal nanoparticles as shown in Fig. S1.
The synthesized AgNPs were collected by centrifugation and
washing several times with double distilled water. The dried AgNPs
2. Experimental
Materials
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were lyophilized in ambient condition. After lyophilisation, the FESEM image of AgNPs (A), GOꢀAgNPs (B) and RGOꢀAgNPs
AgNPs were stored in screw cap bottle for further characterization.
(C).
Fabrication of RGOꢀAgNPs modified GCE
The GO was synthesized according to our previous report
using Hummers method.24 1 mgmL–1 of GO solution was taken to
synthesize the present nanocomposite. In order to prepare the RGOꢀ
AgNPs composite, the asꢀsynthesized AgNPs with different
concentrations (0.5, 1, 2 and 3 mg mL–1) were mixed with GO (1 mg
mL–1) solution and sonicated for 30 min. About 6 µL (optimum) of
GO/AgNPs solution was drop casted on preꢀcleaned GCE surface.
10 consecutive cyclic voltammograms were performed using the
GO/AgNPs modified electrode in the potential range of 0 to ꢀ1.3 V
in pH 5 solution at a scan rate of 50 mV s–1. After 10 successive
consecutive cycles the GO/AgNPs modified electrode was reduced
to RGOꢀAgNPs modified electrode.28 The resulting RGOꢀAgNPs
modified electrode was further used for the detection of NB.
Fig. 1 FESEM images of AgNPs (A), GOꢀAgNPs (B) and RGOꢀ
AgNPs (C). The corresponding EDX of RGOꢀAgNPs.
3. Results and Discussion
As shown in Fig. 1C, the spherical and uniform sized AgNPs
are observed on RGO. The morphology and size of the AgNPs are in
close agreement with the AgNPs on GO (B). The EDX results also
further confirm the presence of metallic Ag, carbon and oxygen in
the RGOꢀAgNPs composite. The particle size distribution histogram
for AgNPs in GOꢀAgNPs and RGOꢀAgNPs composites are shown
in Fig. 2A and B. The histogram of AgNPs in RGOꢀAgNPs
composite indicates that the size of the AgNPs is 40 nm and the
observations are in close agreement with the size of AgNPs in RGO.
These findings further confirm that the size of the AgNPs is not
affected after the electrochemical preparation of RGOꢀAgNPs.
Raman spectroscopy is widely used for the confirmation of the
transformation of GO to RGO. Fig. 2C shows the Raman spectra of
GO (black line), RGO (brown line) and RGOꢀAgNPs (blue line).
The Raman spectra of GO, RGO and RGOꢀAgNPs show the D and
G band at about 1338 and 1509 cm–1, 1339 and 1606 cm–1 and 1339
Characterization of synthesized RGOꢀAgNPs composite
UV–Vis spectroscopy is an important technique to verify
the size, shape, and stability of the nanoparticles. The formation of
AgNPs was visually identified by means of change in colour from
pale greenish yellow to brown.29 Fig. S1 illustrates the UV–Vis
spectra of silver colloid with different time intervals of 10, 30,
60 min. The spectral values were recorded at 445, 452, 453 nm and
they were indexed as S1, S2, S3, respectively. The SPR peak occurs
at 453 nm with high absorbance for AgNPs.30 The absorption peak
steadily increases and after 1 h there is no increase in the absorption
peak, which confirms that the reaction is completed within 1 h. The
intensity of colour does not intensify after 1 h which is established
by UV–Vis spectra. The size and morphology of the synthesized
AgꢀNPs on RGO were determined by FESEM. Fig. 1 displays the
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and 1608 cm–1, respectively. The D and G bands are attributed to the at1649 cm−1 may be assigned to the ꢀOH bending modes. The band
vibrations of sp3 carbon atoms of disordered graphene nanosheets observed at 1514 cm−1 is assigned to Cꢀ C aromatic vibrations.32 The
and vibrations of sp2 carbon atom domains of graphite. The RGO weak band observed at 1400 cm−1 is due to C–H deformation
and RGOꢀAgNPs show higher intensity (1.06) of the D to G band vibrations. The band observed at 1153 cm−1 can be attributed to
(ID/IG) than that of GO (1.0). The result indicates that the high carbonyl group as in aldehydic or ketonic group. The band observed
ability for the recovery of the hexagonal network of carbon atoms at 1028 cm−1 is due to the vibrational stretching frequency modes of
and formation of new graphitic domains. Furthermore, the observed C–O–C of phenolic compounds.33 After the bioreduction of silver
intensity of the G band of RGOꢀAgNPs is higher than RGO, which ion with the Justicia glauca extract, the bands at 3652, 3752 and
is attributed to the polar interaction of AgNPs with RGO. However, 3569 cm−1 remain unaffected but the band intensities have reduced.
the interaction of AgNPs with RGO is relatively low compared to It suggests the possible involvement of –C– of carboxylic group and
GO due to the less oxygenꢀcontaining groups of RGO. These hydroxyl group during the nanoparticles synthesis. The band at 3371
observations further confirm the transformation GOꢀAgNPs to cm−1 is shifted to 3429 cm−1 with broad band intensity, suggesting
RGOꢀAgNPs after the electrochemical reduction process.
that the hydroxyl group plays a vital role during the nanoparticles
synthesis. The sharp band at 2925 cm−1 and minor band at 2850
cm−1 are unaffected but the band intensities have decreased. This
suggests the possible involvement of ꢀC–H– of aromatic ring during
the nanoparticles synthesis. The band at 1741 cm−1 is shifted to 1751
cm−1, suggesting the possible involvement of carbonyl group in the
nanoparticles synthesis. The sharp and narrow band at 1649 cm−1 is
shifted to 1697 cm−1 with diminished band intensity, suggesting that
the excess of hydroxyl groups in aromatic ring involve throughout
the nanoparticles synthesis. The sharp and narrow band at 1514 cm−1
is shifted to 1600 cm−1 with reduced band intensity, confirming the
possible involvement of Cꢀ C aromatic group during the synthesis.
The band at 1400 cm−1 is shifted to 1425 cm−1 with reduced band
intensity, suggesting the involvement of C–H group in aromatic
ring. The band at 1153 cm−1 remains unaffected but the band
intensity has reduced, which suggests the possible involvement of
carbonyl group. The broad band at 1028 cm−1 is shifted to 1018
cm−1 with reduced band intensity, suggesting the involvement of C–
O–C of phenolic compound during the bioreduction process.34–36
Electrochemical properties of RGOꢀAgNPs composite
Fig. 2 The size distribution histogram of AgNPs in GOꢀAgNPs (A)
and RGOꢀAgNPs (B). (C) Raman spectra of GO (black line), RGO
(brown line) and RGOꢀAgNPs (blue line).
Fig. S2 shows the spectra obtained from the powdered
samples of untreated leaf (b) and green synthesized AgNPs (a),
respectively. The band around 3752 and 3652 cm−1 can be assigned
to the –C– of carboxylic group.29 Band around 3569 and 3371 cm−1
can be assigned for the O–H stretching vibration indicating the
presence of hydroxyl group.30 The minor as well as sharp band
observed in the region 2925 and 2850 cm−1 is due to the stretching
vibration of ꢀC–H–.31 The band observed at 1741 cm−1 is attributed
to a carbonyl group. The strong as well as broad band observed
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To evaluate the electrochemical properties of RGOꢀ The redox peak current of Fe(III)/Fe(II) increases with increasing
AgNPs composite, cyclic voltammetry was performed in a 5 mM the scan rate from 50 to 500 mV s−1, and the anodic and cathodic
K3[Fe(CN)6] solution with 0.1 M KCl at a scan rate of 100 mV s–1. peak currents are linear with the square roots of the scan rates (Fig.
Fig. 3A represents the electrochemical behaviour of redox couple of 3B inset). This result indicates that the electrochemical behaviour of
Fe(III)/Fe(II) at bare GCE (a), GOꢀAgNPs/GCE (b) and RGOꢀ Fe(III)/Fe(II) at the modified electrode is a typical diffusion
AgNPs/GCE (c). At bare GCE, a wellꢀdefined redox peaks appear controlled electrochemical process.
with a peakꢀtoꢀpeak separation (ꢁEp) of 136 mV, which indicates
Electrochemical behaviour of NB on RGOꢀAgNPs modified
that the electrochemical process of Fe(III)/Fe(II) at bare GCE is
electrode
reversible.
The electrochemical behaviour of NB on different modified
electrodes was studied by using CV. Fig. 4A depicts the
electrochemical behaviour of NB on (a) bare, (b) AgNPs, (c) GO,
(d) RGO, (e) GOꢀAgNPs, (g) RGOꢀAgNPs modified GCEs in 100
µM NB containing PBS at a scan rate of 50 mV s–1. As can be seen
in curve f (RGOꢀAgNPs), there is no significant peak appeared in
the absence of 100 µM NB, whereas a wellꢀdefined reduction peak
Fig. 3 A) CV response of bare GCE (a), GOꢀAgNPs/GCE (b) and
(R1) is clearly observed at ꢀ0.458 V in the presence of 100 µM NB
RGOꢀAgNPs/GCE (c) in 5 mM K3[Fe(CN)6] solution with 0.1 M
(curve g). The corresponding peak is related to the reduction of NB
KCl at a scan rate of 100 mV s–1. B) CV response of RGOꢀAgNPs
to phenyl hydroxylamine. Although three more peaks are observed
modified GCE in 5 mM K3[Fe(CN)6] solution with 0.1 M KCl at
at RGOꢀAgNPs modified GCE and designated as R2, R3 and O1. The
different scan rates from 50 to 500 mV s–1 (a–j).
peak R2 is due to the formation of aniline from phenyl
In contrast, the current intensities decrease with higher
ꢁEp (374 mV) observed at GOꢀAgNPs/GCE, which is attributed to
the low surface area that retards the electrochemical activity of GOꢀ
AgNPs. However, the Fe(III)/Fe(II) redox couple is highly active on
RGOꢀAgNPs/GCE with increased peak current response with low
ꢁEp (97 mV). This result indicates that the electron transfer kinetics
of Fe(III)/Fe(II) is greatly enhanced by RGOꢀAgNPs composite
compared to other modified electrodes. This is because of the high
conductivity of RGOꢀAgNPs thus improving the electron transfer of
redox couple towards electrode surface. In addition, CVs were also
recorded for the influence of scan rate at the RGOꢀAgNPs/GCE
under similar experimental conditions and are shown in Fig. 3B.
hydroxylamine (R1) and the redox peak R3/O1 is the reversible
behaviour of phenyl hydroxylamine to nitrosobenzene.37 The peak
current of R2 is lower than R1, which indicates that the NB reduction
at RGOꢀAgNPs/GCE is more favoured to form
a phenyl
hydroxylamine in neutral or alkaline medium. On the other hand, the
enhanced reduction peak current response is observed on RGOꢀ
AgNPs modified GCE compared to other modified GCEs.
Moreover, the reduction peak potential of NB shifts toward positive
direction at RGOꢀAgNPs modified electrode by 151, 276, 255 and
250 mV compared to GOꢀAgNPs (e), RGO (d), AgNPs (b) and (a)
bare GCEs, respectively. The result demonstrates that the decrease
in overpotential of RGOꢀAgNPs electrode toward NB is attributed to
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the strong π–π interaction between the NB and RGO and more AgNPs (0.5, 1, 2 and 3 mg/mL; curve a’–d’) at RGOꢀAgNPs
active sites of AgNPs.38 The firm attachment of AgNPs on RGO modified GCE in PBS at a scan rate of 50 mVs–1.
nanosheets is due to the polar interaction of AgNPs with oxygen
functional groups of RGO.
The effect of different concentrations of AgNPs on the
electrochemical response of NB in RGO was further studied by
using CV. The different concentrations of GOꢀAgNPs dispersions
were prepared by dispersing AgNPs (0.5, 1, 2 and 3 mg/mL) in GO
solution by sonication. Fig. 4B shows the CV response of 100 µM
NB containing PBS at different concentrations of AgNPs loaded
RGO modified electrode at a scan rate of 50 mV s–1. The utmost
cathodic peak current response is observed for 2 mg/mL AgNPs
dispersed RGO. As shown in Fig. 4B inset, the maximum anodic
and cathodic peak current of AgNPs at RGO is observed for 2
mg/mL AgNPs dispersion. The current response of AgNPs decrease
in the concentration of AgNPs above or below 2 mg/mL dispersion.
Hence 2 mg/mL AgNPs dispersed GO solution was used for the
RGOꢀAgNPs electrode fabrication and chosen as an optimum for
further electrochemical studies for NB.
Fig. 5A shows the CV responses of RGOꢀAgNPs modified
electrode in 100 µM NB containing PBS at a scan rate of 50 mV s–1.
The reduction peak current of NB increases with increasing the scan
rates from 20 to 200 mVs–1 (a–j) and the peak potential (Epc) shifts
slightly towards negative potential. The reduction peak current
response of NB has a linear relationship with the square root of scan
rates (Fig. 5A inset). The linear regression equation is found to be
Ip (µA) = 1.2798 ν1/2 (mVs–1)1/2 + 5.5565; R2 = 0.9938. The result
indicates that the electrochemical reduction of NB at RGOꢀ
AgNPs/GCE is a diffusion controlled irreversible electrode process.
The irreversible electrochemical behaviour NB is confirmed from
the plot of Epc vs. logν (Fig. S3) and the corresponding linear
regression equation can be expressed as, Epc (V) = –0.0899 logν –
0.2858; R2 = 0.9983. According to the Tafel equation, the above
Fig. 4 A) CVs obtained at (a) bare, (b) AgNPs, (c) GO, (d) RGO, (e)
GOꢀAgNPs, (g) RGOꢀAgNPs modified GCEs in 100 µM NB
containing PBS at a scan rate of mVs–1. At same conditions, RGOꢀ
AgNPs modified GCEs in the absence of 100 µM NB (f). B) CV
response of different concentrations of AgNPs (0.5, 1, 2 and 3
mg/mL; curve a–d) at RGOꢀAgNPs modified GCE in 100 µM NB
containing PBS at a scan rate of 50 mVs–1. Inset; CV response of
RGOꢀAgNPs modified GCE with the different concentration of
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relationship
can
be
expressed
as: solutions from 3 to 11(a–e). Upper inset: the plot of Ipc vs. pH;
Lower inset: the Epc vs. pH.
ꢒ1ꢓ
ꢀꢁꢂ ꢃ ꢄ ꢅ.ꢆꢇꢆꢈꢉ ꢍꢎꢏ ꢐ ꢑ
ꢅꢊꢋꢌ
Where, R is the gas constant (8.314 JK–1 mol–1), T is the
room temperature (298 K), α is the electron transfer coefficient, n is
the number of electrons transferred and F is the Faraday’s constant
(96485 C mol–1) and α value is calculated as 0.66. The Tafel slope, b
= 2.303RT/αnF, value is calculated to be 89.9 mV/decade which is
higher than 60 mV.39, 40 The obtained b value clearly indicates that
one electron is involved in the rate determining step. The
electrochemical reduction of NB is evaluated by CV at RGOꢀAgNPs
modified electrode in the presence of 100 µM NB containing
different pH solutions (pH 3, 5, 7, 9 and 11,(a–e)) as depicted in
Fig. 5B. Upon increasing the pH from 3 to 7 (upper inset), the Ipc
increases gradually up to 7 and then decreases at higher pH with
negative potential shift (lower inset). This result suggests that the
electrochemical reduction of NB is pH dependent and hydrogen ion
concentration may affect the rate of reduction reaction. In addition,
the reduction product of NB, phenyl hydroxylamine, is more active
in neutral and/or higher pH range.41 Hence, the pH 7 was chosen as
an optimum pH for further analytical studies of NB.
Electrochemical determination of NB RGOꢀAgNPs modified
electrode
The electrochemical determination of NB was done at
RGOꢀAgNPs modified electrode in PBS by using DPV. Fig. 6
depicts DPV response of RGOꢀAgNPs modified electrode in
different concentrations of NB from 0.5 to 900 µM (a–r) containing
PBS. It can be seen that a sharp reduction peak is observed for the
addition of 0.5 µM NB and the reduction current increases with
increasing the concentration of NB. The reduction peak current
response increases linearly up to 900 µM (Fig. 6B inset). The
calibration plot for Ipc versus different concentrations of NB is found
to be Ipc = 0.0663 [NB]/µM + 1.5981 with the correlation coefficient
Fig. 5 A) CV response of RGOꢀAgNPs/GCE in 100 µM NB
containing PBS at different scan rates range from 20 to 200 mVs–1
(a–j) and inset shows the plot of Ipc vs. square roots of scan rates. B)
CV response for 100 µM NB at RGOꢀAgNPs/GCE in different pH
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of 0.9965. The sensitivity is calculated as 0.836 µAµM–1 cm–2. The phenol (4ꢀNP), 4ꢀnitro toluene (4ꢀNT), cadmium (Cd2+) and lead
limit of detection (LOD) is estimated to be 0.261 µM.
(Pb2+) respectively. The nitroaromatic compounds such as 4ꢀBr NB,
4ꢀCl NB, Cd2+ and Pb2+ show less interfering effect of about 3.6 %
on the NB detection.
Fig. 6 DPV response of RGOꢀAgNPs/GCE for PBS containing
different concentrations of NB in the concentration range of 0.5–900
µM (a–r). Inset: the calibration plot of Ipc vs. [NB]/µM
Fig. 7 Effect of addition of 5 fold interference species on the
cathodic peak current response of 100 µM NB at RGOꢀ
AgNPs/GCE. Tested interfering species (x axis); 4ꢀbromo NB (4ꢀBr
NB), 4ꢀchloro NB (4ꢀCl NB), 4ꢀnitroaniline (4ꢀNA), 4ꢀnitrobenzoic
acid (4ꢀNBA), 4ꢀacetamido phenol (4ꢀAP), 4ꢀnitro phenol (4ꢀNP)
and 4ꢀnitro toluene (4ꢀNT); 10ꢀfold of cadmium (Cd2+) and lead
(Pb2+). Peak current response of 100 µM NB changed (y axis).
The analytical performance such as LOD, sensitivity, linear
response range of the sensor was compared with previously reported
NB sensors and the comparative results are shown in Table 1. It can
be seen that the developed NB is more comparable with the
previously reported NB sensors.42–48 Thus, it can be used for
sensitive detection of NB in environment samples.
Whereas the other nitroaromatic compounds significantly
affect the peak current response of NB owing to their similar
structural activity, the response current of NB is changed only 6.8 %
in the presence 5ꢀfolds concentration of nitroaromatic compounds,
which indicate that the fabricated modified electrode is more
suitable for selective determination of NB in the presence of
nitroaromatic compounds and metal ions.
Selectivity study
In order to study the effect of interference, the DPV was
performed at RGOꢀAgNPs modified electrode for the response of
100 µM NB in the presence of different nitroaromatic compounds
and some potentially interfering metal ions. Fig. 7 represents the
percentage of relative error for the determination of NB with 5ꢀfold
of organic and 10ꢀfold of metal ions, such as 4ꢀbromo nitrobenzene
(4ꢀBr NB), 4ꢀchloro nitrobenzene (4ꢀCl NB), 4ꢀnitroaniline (4ꢀNA),
4ꢀnitrobenzoic acid (4ꢀNBA), 4ꢀacetamido phenol (4ꢀAP), 4ꢀnitro
Determination of NB in real sample analysis
The practical viability of the fabricated RGOꢀAgNPs
modified electrode was evaluated for the determination of NB in
waste water samples. The waste water samples were collected from
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outside the university premise. The DPV was used for the electrodes. The fabricated electrode shows many advantages, such
determination of NB and the waste water did not show any response as good sensitivity, low LOD, wide linear response range along with
for NB, which reveals that no NB contamination was found in the good selectivity for NB determination. A good recovery result of
collected waste water samples. Under similar experimental NB in waste water samples indicates the good practicality of the
conditions, the different concentration of NB was spiked into the developed sensor. The fabricated sensor can be further extended for
waste water samples and the recovery results were calculated by the the sensitive trace level detection of NB in environmental samples.
standard addition method. The recovery result along with relative
Acknowledgments
standard deviation (RSD) is summarized in Table 2. The good
The support of the visiting professorship to SMC at the King Saud
recovery results with a range of about 98.2 – 100.8 % is obtained
University is gratefully acknowledged.
using the fabricated electrode and the RSD values for three samples
Notes and references
are of 2.96, 2.63 and 3.22 %, respectively. These good recovery
aElectroanalysis and Bioelectrochemistry Lab, Department of Chemical
results and RSDs of the developed sensor prove the good
Engineering and Biotechnology, National Taipei University of
practicality towards the determination of NB in waste water
samples.
Technology, No. 1, Section 3, ChungꢀHsiao East Road, Taipei 106,
Taiwan, ROC. Eꢀmail: smchen78@ms15.hinet.net;
Fax: +886ꢀ2ꢀ27025238; Tel: +886ꢀ2ꢀ27017147.
Stability, repeatability and reproducibility studies
bDepartment of Chemistry, Thiagarajar College, Maduraiꢀ625009,
Tamilnadu, India
The electrode stability is most significant factor for all
newly developed sensors. The reduction peak current response of E mail: kmpprakash@gmail.com;
Fax: +91ꢀ4522312375, Tel: +91ꢀ9842993931, +91ꢀ4522456783.
100 µM NB at RGOꢀAgNPs modified electrode was examined up to
52 days by CV and stored in PBS when not in use. The modified
electrode retains about 90.15 % of its initial current response after
52 days, which indicates the excellent storage stability of the sensor.
To evaluate the repeatability and reproducibility of the developed
sensor, the CVs were performed for the reduction of 100 µM NB in
PBS. The acceptable repeatability with the RSD of 4.2 % is found
for single electrode in 5 different measurements. The fabricated
sensor shows a satisfactory reproducibility with the RSD of 3.80 %
for determination of NB using 5 different sensors.
cDepartment of Botany and Microbiology, College of Science, King Saud
University Riyadh 11451, Saudi Arabia
dChemistry Division, Center for General Education, Chang Gung
University, TaoꢀYuan, Taiwan. Eꢀmail: blou@mail.cgu.edu.tw
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DOI: 10.1039/C5RA00992H
Table 1 Comparison of the analytical parameters (linear range,
Modified electrode
Linear range
(µM)
Sensitivity
(µAµM–1 cm–2)
–
LODa
(µM)
10
Ref.
OMCb/DDABc/GCEd
BiFe/CPEf
20–2900
[42]
[43]
[44]
[45]
[46]
[47]
[48]
1–100
3–30
0.289
–
0.83
1.1
ATPꢀAgg/GCE
PNMPCh/Nafion/GCE
OMCNi/GCE
1–200
6.93
0.675
–
0.05
0.18
0.38
0.06
0.26
0.5–1000
0.528–132
1–3900
0.5–900
TMPPj/NꢀOMCk/GCE
PdlꢀGGꢀgꢀPAMmꢀsilica/GCE
RGOnꢀAgNPso/GCE
0.026
0.836
Present
work
sensitivity and LOD) of proposed GOꢀAgNPs modified electrode
with other modified electrodes for the determination of NB.
aLOD – limit of detection; bOMC – ordered mesoporus carbon;
cDDAB – didodecyldimethylammonium bromide; dGCE – glassy
carbon electrode; eBiF – bismuthꢀfilm; fCPE – carbon paste
electrode; gATPꢀAg – attapulgiteꢀsilver nanocomposites; hPNMPC –
platinum nanoparticles/macroporous carbon; iOMCN – ordered
mesoporous carbon nitride; jTMPP
–
tetra(4ꢀmethoxyphenyl)
k
l
porphyrin; NꢀOMC – Nꢀdoped ordered mesoporous carbon; Pd –
palladium nanoparticles; mGGꢀgꢀPAM
–
guar gum grafted
n
o
polyacrylamide; RGO – reduced graphene oxide; AgNPs – silver
nanoparticles.
Sample
Added
(µM)
15
Founda
(µM)
15.13
29.82
58.97
Recovery (%)
RSDb
(%)
Waste water 1
Waste water 2
Waste water 3
100.8
99.4
98.2
2.96
2.63
3.22
30
60
Table 2 Electrochemical determination of NB in waste water
samples using RGOꢀAgNPs/GCE by DPV. (n=3)
aStandard addition method; bRelative standard deviation of three
measurements.
12 | J. Name., 2012, 00, 1-3
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