Preparation of novel nanocomposite consisting of bismuth particles, polypyrrole and multi-walled carbon nanotubes for simultaneous voltammetric determination of cadmium(II) and lead(II)

Synthetic Metals 253 (2019) 1–8

Contents lists available at ScienceDirect

Synthetic Metals journal homepage: www.elsevier.com/locate/synmet

Preparation of novel nanocomposite consisting of bismuth particles, polypyrrole and multi-walled carbon nanotubes for simultaneous voltammetric determination of cadmium(II) and lead(II) Larbi Oularbia,b, Mireille Turmineb, Mama El Rhazia, a b

T

⁎

University Hassan II Casablanca, Faculty of Science and Technology, Laboratory of Materials Membranes and Environment, P.B 146, Mohammedia 20800, Morocco Sorbonne University, CNRS, Laboratoire Interfaces et Systèmes Electrochimiques, 4 place Jussieu, F-75005, Paris, France

A R T I C LE I N FO

A B S T R A C T

Keywords: Carbon paste electrode Polypyrrole Multi-walled carbon nanotubes Bismuth particles Heavy metals ions Square wave voltammetry

A carbon paste electrode (CPE) modified with a nanocomposite consisting on functionalized multiwalled carbon nanotubes, polypyrrole film (PPy) and bismuth particles is described for simultaneous determination of Pb(II) and Cd(II). The structural and surface properties of the functionalized multiwalled carbon nanotubes and the nanocomposite were investigated by Fourier transform infrared spectroscopy and field-emission gun scanning electron microscopy. The electrical properties were studied by cyclic voltammetry and electrochemical impedance spectroscopy. The modified CPE was applied to the determination of Pb(II) and Cd(II) using square wave anodic stripping voltammetry. Under optimized conditions, the calibration plot is linear in the range from 0.11 to 120 μg L−1 for Pb(II) and 0.16 to 120 μg L−1 for Cd(II), the detection limits are 99 and 157 ng L−1, respectively. The sensor was applied to analysis of Pb(II) and Cd(II) in spiked real samples of tap water and gave satisfactory results.

1. Introduction Heavy metal poisoning has generated increasingly worried because of their high toxicity and their harmful effects over health, genetic, nutritional, and ecosystems [1]. Lead (Pb2+) and cadmium (Cd2+) are considered as widespread highly toxic heavy metal ions even at trace levels. They can be accumulated in the human’s body and causes several health problems such as cancer, liver dysfunction, disturbance in endocrine and nervous systems, etc [2]. Therefore, the determination of heavy metal ions in natural and drinking water has attracted considerable attention. Several sophisticated and standard methods were used for the determination of traces heavy metal ions including atomic absorption spectroscopy (AAS), inductively coupled plasma coupled to mass spectroscopy (ICP-MS), gas chromatography coupled to mass spectroscopy (GC–MS) [3–5]. However, these methods require a heavy, an expensive and a sophisticated equipment, in addition a skilled personnel and sometimes a long prior sample preparation. Electrochemical methods including square wave voltammetry anodic stripping voltammetry (SWASV) or differential pulse voltammetry (DPASV), have been widely used as a powerful alternatives tools to classical methods for the determination of trace heavy metal ions due to their low cost, easy operation, high sensitivity and a rapid response time [6–9]. The main

⁎

challenge in electrochemical methods using electrodes as sensors is to increase the reactivity of the surface towards the analyte. Indeed, the slow redox reaction of analytes on the electrodes surface requires a suitable modification of their surfaces, which can play crucial roles in the performance of sensor [10,11]. Recently, the integration of nanocomposites in electrode fabrication as sensing platforms for heavy metal ions has gained more attention due to their unique structure, which offers large active surface, good electrical conductivity and excellent catalytic properties [12–16]. Therefore, several nanocomposites modified electrodes based on conducting polymers (CPs), carbon nanomaterials (CNM) or metal nanoparticles (MNPs) were reported for the determination of Pb2+, Cd2+ and many other heavy metal ions [10,11]. Song et al., reported a porous composite of graphene oxide (GO) and polypyrrole (PPy) modified gold disk electrode for the determination of Cd2+ [8]. The porous composite pGO/PPy was electrochemically synthetized using cyclic voltammetry. Deshmukh et al., modified a stainless steel electrode (SSE) with a nanocomposite consisting on polypyrrole, single-walled carbon nanotubes (SWCNT) and ethylenediaminetetraacetate (EDTA) EDTA-PPy/SWCNT/SSE for determination of Pb2+ using DPV [17]. In another work, the same authors reported a nanocomposite of polyaniline (PANi), SWCNT and EDTA for determination of trace copper (Cu2+) [7]. A nanocomposite of multi-

Corresponding author at: Faculty of Sciences and Technologies, BP 146 Mohammedia 20650, University Hassan II of Casablanca, Morocco. E-mail address: [email protected] (M. El Rhazi).

https://doi.org/10.1016/j.synthmet.2019.04.011 Received 11 January 2019; Received in revised form 6 April 2019; Accepted 10 April 2019 0379-6779/ © 2019 Elsevier B.V. All rights reserved.

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

using a Sotelem Potentiostat coupled with a frequency response analyzer FRA, Solarton-1254. All the electrochemical measurements were carried out in a conventional three-electrode system comprising of a platinum grid as counter electrode, a saturated calomel electrode (SCE) (Radiometer) as reference electrode and CPE or modified CPE as working electrode.

walled carbon nanotubes (MWCNT) and magnetite nanoparticles (Fe3O4) modified glassy carbon electrode (GCE), was described for simultaneous voltammetric determination of heavy metals [18]. Gold nanoparticles (AuNP) were electrochemical deposited on the reduced graphene oxide to obtain a nanocomposite electrode for the determination of trace arsenic (As3+) [19]. Bismuth-based electrodes are also a promising and alternative material to mercury electrodes due to its low toxicity, high sensitivity, a wide range of cathodic potential, and its insensitivity to dissolved oxygen. The combination of bismuth with different materials such as conducting polymers [20], carbon nanomaterials [21], metal nanoparticles [22], ionic liquids [23] have been reported to analyze heavy metal ions. Tseliou et al., reported exfoliated bismuth telluride (Bi2Te3) combined with graphene oxide (GO) as an hybrid film-modified GCE for simultaneous determination of Pb2+ and Cd2+ [24]. Riman et al., modified screen-printed carbon electrode (SPCE) with bismuth oxide (Bi2O3) using park discharge. The Bi2O3/ SPCE was applied for determination of Pb2+ and Cd2+ [25]. Jeromiyas et al., reported bismuth nanoparticles decorated carbon nanotubes modified SPCE for mercury detection [26]. Nanoporous bismuth electrode was also reported for determination of heavy meats ions [27]. However, most of the reported nanocomposites require complex and longer preparation and only a few papers have been devoted to hybrid nanocomposites based on conducting polymers, carbon nanomaterials and metals particles for determination of Pb2+ and Cd2+. In the present investigation, we reported for the first time a facile eco-friendly synthesis of the nanocomposite Bi/PPy/MWCNT modified carbon paste electrode (CPE) for simultaneous determination of trace Pb2+ and Cd2+. The elaboration of our sensor consists of two steps: the first one involves the deposition of functionalized multi-walled carbon nanotubes on the surface of carbon paste electrode followed by the electrosynthesis of polypyrrole film using galvanostatic mode. In the second step, the prepared electrode was modified with bismuth particles by performing an in-situ modification in acetate buffer containing a fixed concentration of bismuth ions (Bi3+) and the targets metal ions. The structural and electrochemical features of the functionalized multiwalled carbon nanotubes and the nanocomposite Bi/PPy/MWCNT were examined. The SWASV was used to study the analytical performances for the simultaneous determination of traces Pb2+ and Cd2+. The experimental conditions that affect the analysis of Pb2+ and Cd2+ were optimized. The selectivity, repeatability, reproducibility, stability and application of the developed sensor were also investigated.

2.3. Electrochemical measurements Cyclic voltammetry (CV) measurements was performed in 0.25 M LiClO4 solution in the range of potential from +0.3 to -0.8 V/SCE at a scan rate of 50 mV s−1. Electrochemical impedance spectroscopy (EIS) analysis were carried out in 0.25 M LiClO4 solution, at different potential values in the range of frequency from 60 kHz to 10 mHz with 7 points per decade and an applied voltage perturbation of 10 mV. Before each impedance measurement, the electrode was kept to the potential of analysis for 10 s as an equilibrium period. 2.4. Procedure for Cd2+ and Pb2+ detection Square wave anodic stripping voltammetry (SWASV) measurements were performed in acetate buffer containing 350 μg L−1 of Bi3+ and a predetermined concentration of Cd2+ and Pb2+ ions. Then a deposition potential of -1.2 V/SCE is applied to the working electrode during 240 s under continuous magnetic stirring. The square wave voltammograms (SWVs) were recorded by applying a potential ranging from -1 to -0.2 V/SCE, a scanning frequency of 50 Hz, an amplitude of 50 mV and a step potential of 5 mV. After each measurement, the surface of the electrode was cleaned by applying a potential of +0.3 V/SCE during 10 s under continuous magnetic stirring. 2.5. Preparation of the modified electrodes 2.5.1. Functionalization of the MWCNT The functionalization of MWCNT is a key step to have a good dispersion of MWCNT in the nanocomposite, in addition to eliminate the impurities formed during the production process such as graphitic nanoparticles, amorphous carbon and metallic catalyst nanoparticles, etc. An appropriate amount of MWCNT was dispersed in a mixture of concentrated H2SO4 and HNO3 at a volume ratio of 1:3 under ultrasonic agitation during few minutes then refluxed at 80 °C under magnetically stirring for 4 h. The MWCNT were then filtered on a Millipore polycarbonate membrane (Ø 0.22 μm) and washed with bidistilled water until the filtrate reaches a neutral pH value. Finally, the functionalized MWCNT were dried under vacuum at 50 °C during 5 h.

2. Experimental procedures 2.1. Chemicals and reagents Pyrrole monomer was obtained from ACROS Organics. MWCNT with an outside diameter of 6–13 nm and a length of 2.5–20 μm, graphite powder with a particle size less than 20 μm, paraffin oil, lead (II) nitrate Pb(NO3)2 (ACS reagent, ≥ 99%), cadmium nitrate Cd(NO3)2 (purum p.a., ≥ 99%), bismuth nitrate Bi(NO3)3 (reagent grade, ≥ 98%) and lithium perchlorate LiClO4 (purum p.a., 98%) were purchased from Sigma-Aldrich. Potassium chloride KCl (99%) and nitric acid HNO3 (68%) were procured from AnalaR NORMAPUR, and sulfuric acid H2SO4 (98%) from Fluka. Sodium acetate CH3COONa (Anhydrous 99%) from ACROS Organics and acetic acid CH3COOH (99%) from Sigma Aldrich. Other solvents and chemicals were of analytical grade.

2.5.2. Bare carbon paste electrode (CPE) The carbon paste electrode (CPE) was prepared according to our previous paper [13]. Briefly, a mass of 1 g of graphite powder was mixed with 300 μL of paraffin oil in a mortar until a uniform paste was obtained. A portion of the obtained paste was packed into the cavity of the electrode of a Teflon tube (Ø 3 mm). The electrode was then polished on a clean paper until a smooth surface was obtained. A stainlesssteel rod was used to ensure the electrical contact. 2.5.3. MWCNT modified CPE A suspension of MWCNT with a concentration of 1 mg mL−1 was prepared by dispersing the functionalized MWCNT in the bidistilled water under ultrasonic vibrating. Then a volume of 10 μL of the dispersed MWCNT was dropped on the CPE surface and dried at room temperature. The modified electrode was named MWCNT/CPE.

2.2. Instruments The Fourier transform infrared (FTIR) spectra were recorded on Bruker IFS 66/S spectrometer. Scanning electron microscopy (SEM) was carried out using Zeiss SUPRA 55-VP. Cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements were performed using an Autolab Potentiostat/Galvanostat model PGSTAT100 with GPES 4.9 software. Electrochemical impedance measurements were carried out

2.5.4. PPy modified bare CPE and MWCNT-CPE Electrochemical deposition of PPy on bare CPE and MWCNT/CPE was performed in an aqueous solution containing 0.1 M pyrrole and 0.5 M LiClO4 using galvanostatic mode at a current density of 0.2 mA 2

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

cm−2. The modified electrodes were then washed with bidistilled water, dried under a gentle stream of nitrogen gas. The modified electrodes were named respectively PPy/CPE and PPy/MWCNT/CPE.

which is characteristic to the PPy film. For PPy/MWCNT (Fig. 2, blue line), the same behavior is noticed with a pair of peaks well-defined. In addition, the current was gradually increased compared to PPy/CPE, with a peak-to-peak separation of about 230 mV. This result confirms the role of the MWCNT to promote the electron transfer of the PPy film by providing a high active surface area and an easier electron transfer as reported by other authors using different nanocomposites of CPs/ MWCNT such as P-1,5-DAN/MWCNT [32].

3. Results and discussion 3.1. FTIR characterization of MWCNT and electrodeposition of PPy Fourier Transform Infrared (FTIR) spectroscopy analysis was used to characterize the surface of the MWCNT before and after their acid treatment, Fig. S1 A (Supporting information) shows the recorded FTIR spectra. It can be seen that the functionalized MWCNT exhibited new peaks compared to raw MWCNT. The three bands located at 3453, 1736 and 1109 cm−1 are characteristic to the carboxylic groups (−COOH), which are respectively attributed to the stretching vibration of the hydroxyl (−OH), carbonyl (C]O) and epoxy (C–O) groups. The broad peak at 2366 cm−1 is associated with the −OH stretch of strongly hydrogen-bonded of the carboxylic groups (eCOOH) [13,28]. The obtained results showed clearly that the treated MWCNT were successfully oxidized by creating new functional groups on their surface. The electrodeposition of PPy film on CPE and MWCT/CPE was performed using galvanostatic mode, Fig. S1B shows the chronopotentiometric curves obtained during the deposition of PPy on both electrodes. The polymerization of pyrrole consists of two major steps, the nucleation and the growth of PPy film. The maximum electrode potential at the PPy/CPE and MWCNT/CPE are of about ˜ 0.6 and ˜ 0.47 V/SCE respectively. The difference of the potential can be attributed to the presence of charge carriers on the MWCNT sheets, indicating an interaction between the MWCNT sheets and PPy chain during the electropolymerization of PPy. From these results, it can be concluded that the MWCNT and the PPy was successfully combined, these are in accordance with the results reported in the literature during the polymerization of PPy on GO [29,30].

3.4. Electrochemical impedance spectroscopy (EIS) characterization Fig. 3 shows the typical Nyquist plots recorded for the PPy/CPE and PPy/MWCNT/CPE at a partially and fully reduced of the PPy film. The charge transfer resistance (R ct ) and the capacity of the film (Cf ) were determined by fitting impedance data using Randles equivalent circuit. Table 1 summarized the results of the simulation. From the (Fig. 3A) of PPy film partially reduced the Nyquist plot of PPy/CPE showed a small semicircle characteristic to the charge transfer resistance (R ct ) of about 100 Ω cm2. At the PPy/MWCNT/CPE, the R ct was significantly decreased to 8 Ω cm2, indicating that the PPy and MWCNT were successfully assembled on the electrode surface. At PPy film fully reduced (Fig. 3B), the PPy/CPE showed a high charge transfer resistance (R ct ) and a dramatic decrease of the capacitance (Cf ) are respectively of about 650 Ω cm2 and 0.1 m F cm−2. While on PPy/ MWCNT/CPE the R ct was not changed, we observe only a slight decrease of the capacitance (Cf ) which is of about 5.41 μF cm−2. This indicates that the electronic transfer on PPy/MWCNT is easier than in the case of PPy/CPE. Since the PPy film on the CPE is relatively thick compared to the PPy film deposited on the MWCNT of a highly porous reticular structure, the neutralization of charge inside the PPy film is easier at PPy/MWCNT than on PPy/CPE [33]. Consequently, it can be concluded that the formed nanocomposite PPy/MWCNT on CPE presents a high electrical conductivity even at a reduced state; this is attributed to the presence of MWCNT, which promotes the electronic transfer and increases the active surface.

3.2. SEM characterization of the modified electrodes

3.5. Square wave anodic stripping voltammetry (SWASV) analysis of Pb2+ and Cd2+

The surface morphology of the modified electrodes was characterized by SEM as shown in Fig. 1. SEM image of bare CPE (Fig. 1A) demonstrates irregularly shaped graphite flakes with different sizes isolated from each other. At the MWCNT/CPE (Fig. 1B), it can be seen that the MWCNT were uniformly dispersed on the electrode surface and forming a porous reticular three-dimensional structure. This structural morphology can provide a much active surface area than in the case of bare CPE. PPy film modified CPE (Fig. 1C) is uniformly covered the electrode surface and shown a structure like tiny grains with almost the same size. At the PPy/MWCNT modified CPE (Fig. 1D) the MWCNT exhibit thicker and smooth tubes wall compared to unmodified MWCNT displaying that the PPy-MWCNT nanocomposite was successfully synthesized on the CPE. The PPy/MWCNT/CPE modified with Bismuth (Fig. 1E) by in-situ deposition at a concentration of 350 μg L−1 of Bi3+ and a deposition potential of -1.2 V/SCE during 240 s, shows a homogeneous and uniform growth of bismuth particles along the PPy/ MWCNT nanocomposite. Such structure can provide a larger specific surface area and an effective reduction of metal ions.

Since our main objective is the application of the nanocomposite MWCNT/PPy combined with Bismuth particles as sensing material, the modified electrode MWCNT/PPy/CPE was applied as sensor for simultaneous detection of traces Pb2+ and Cd2+ using square wave anodic stripping voltammetry (SWASV). Preliminary experiments were carried out to compare the anodic stripping voltammetry response of different electrodes. Fig. 4 shows the square wave anodic stripping voltammograms of 150 μg L−1 Pb2+ and Cd2+ obtained at different modified electrodes under preliminary selected experimental conditions: 0.1 M acetate buffer (pH 4.5) as supporting electrolyte and a deposition potential of −1 V/SCE applied during 120 s. On the bare CPE, a small stripping peak currents of Cd2+ and Pb2+ was observed. However, after its modification with MWCNT the current intensity of Cd2+ and Pb2+ was enhanced, mainly due to the enhancement of the active surface. In the case of PPy/CPE, the stripping peak currents of Cd2+ and Pb2+ was further increased. This improvement can be attributed to the amino groups containing along the PPy chains which are able to chelates Pb2+ and Cd2+ [34,35]. At the PPy/ MWCNT/CPE the peak currents of Pb2+ and Cd2+ was increased more than that on both unmodified or modified CPE. The increase of current intensity can be attributed to the synergic effects of the PPy/MWCNT by improving the conductivity and the surface-active, which leads to an increase of amount of Pb2+ and Cd2+ reduced during the deposition step. After the addition of Bi3+ at a concentration of 350 μg L−1, the stripping peak currents was twofold increase compared to the PPy/ MWCNT/CPE. This response is due to the Bismuth particles able to form alloys with the target metals, this facilitates the nucleation process

3.3. Cyclic voltammetry (CV) characterization of the modified electrodes The different modified electrodes were characterized by cyclic voltammetry in 0.25 M LiClO4 aqueous solution at a scan rate of 50 mV s−1 in a potential ranged from +0.3 to -0.8 V/SEC. Fig. 2 displays the cyclic voltammograms obtained at different modified electrodes. The bare CPE (Fig. 2, magenta line) showed a low background current, while the MWCNT/CPE (Fig. 2, black line) exhibited a small reduction peak at a potential around of -0.4 V/SCE attributed to the insertion of Li+ into the thin film of MWCNT as reported by Barisci et al [31]. At the PPy/CPE (Fig. 2, red line), a redox behavior is observed 3

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

Fig. 1. SEM images of: A) bare CPE, B) MWCNT/CPE, C) PPy/CPE, D) PPy/ MWCNT/CPE and E) Bi/PPy/MWCNT/CPE.

during the deposition of Pb2+ and Cd2+ [36]. 3.6. Optimization of experimental conditions In order to optimize the response of the proposed sensor for the simultaneous detection of traces Pb2+ and Cd2+, the influence of various experimental conditions including Bi3+ concentration, accumulation potential, and accumulation time on the sensing performance of BiPPy/MWCNT/CPE were investigated. The effect of the concentration of bismuth (Bi3+) on the stripping analysis of 100 μg L−1 Pb2+ and Cd2+ was examined in the range of concentration between 100–1000 μg L-1 (not shown). The stripping peak currents of Cd2+ and Pb2+ increase linearly with the increase of the concentration of Bi3+ to reach a high value at a concentration of 350 μg L-1, when the concentration of Bi3+ was further than 350 μg L-1 the anodic stripping peak currents of Pb2+ and Cd2+ decreased. This phenomenon might be attributed to the formation of thick bismuth film on the electrode surface, which is not favorable to the reduction of Pb2+ and Cd2+ [23]. Consequently, a concentration of 350 μg L-1 of Bi3+ was selected as an optimum concentration for the further studies. The influence of deposition potential on the stripping peak currents of 100 μg L−1 Pb2+ and Cd2+ was studied over a potential range of -0.8 to -1.4 V/SCE in 0.1 M acetate buffer (pH 4.5). As shown in Fig. S2A, the height stripping peak currents of Pb2+ and Cd2+ were obtained at a deposition potential of -1,2 V/SCE. Further increase of reduction potential lead to a decrease of current intensity of Pb2+ and Cd2+, this can be attributed to hydrogen formation on the electrode surface reducing its active surface area [15]. Thus, the deposition potential at -1.2 V/SCE

Fig. 2. Typical cyclic voltammograms of bare CPE (magenta line), MWCNT/ CPE (black line), PPy/CPE (red line), and PPy/MWCNT/CPE (blue line) in 0.25 M LiClO4 at scan rate of 50 mV s−1 from +0.3 to -0.8 V/SCE (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

4

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

Fig. 4. SWASV voltammograms of 150 μg L−1 Pb2+ and Cd2+ at different modified electrodes recorded in 0.1 M acetate buffer pH 4.5.

duration of analysis, was selected as an optimum deposition time. 3.7. Analytical features of the Bi-PPy/MWCNT/CPE Using the modified electrode Bi-PPy/MWCNT/CPE under optimized experimental conditions, the SWASV for the simultaneous determination of Pb2+ and Cd2+ at different concentration ranging from 0.11 to 150 μg L−1 for Pb2+ and 0.16 to 150 μg L−1 for Cd2+ were elaborated as illustrated in Fig. 5. It can be seen that the stripping peak currents (Ip) of Pb2+ and Cd2+ increases linearly with the increase of their concentrations from 0.11 to 120 μg L−1 for Pb2+ and 0.16 to 120 μg L−1 for Cd2+. The linear regression equation were: Ip (μA) = 1.1228 C Pb2 + (μg L-1) + 8.0345 and Ip (μA) = 0.4721 C Cd2 + (μg L-1) + 1.5271 for Pb2+ and Cd2+ respectively, with a high correlation coefficient of about R2 = 0.9968 for Pb2+ and R2 = 0.9946 for Cd2+. The limit of Fig. 3. Nyquist plots of PPy/CPE (red dots) and PPy/MWCNT/CPE (blue dots) in 0.25 M LiClO4: A) film partially reduced (-0.200 V/SCE) and B) film fully reduced (-0.500 V/SCE) (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). Table 1 Impedance parameters obtained by fitting the impedance data. Film partially reduced

Film fully reduced

Estimated parameters

Rct /Ω cm2

Cf /mFcm−2

Rct /Ω cm2

Cf /mFcm−2

PPy/CPE PPy/MWCNT/CPE

100 8

2.59 7.28

650 9

0.10 5.41

was selected as an optimal deposition potential for the next experiments. The deposition time plays a key role in striping analysis; it can greatly affect the sensitivity and the detection limit of the method. The effect of deposition time on anodic stripping analysis of 100 μg L−1 Pb2+ and Cd2+ was studied from 60 to 420 s in 0.1 M acetate buffer (pH 4.5) containing 350 μg L-1 of Bi3+ at a deposition potential of -1.2 V/ SCE as shown in Fig. S2B. The stripping peak currents gradually increased with the increase of the deposition time. A highest response was obtained at a deposition time of 360 s, further increase of the deposition time leads to a decrease in the anodic stripping peak currents due to the saturation of the electrode surface. As a result, a deposition time of 240 s, which is included between a high signal and a reasonable

Fig. 5. SWASV of the simultaneous detection of Pb2+ and Cd2+ using Bi-PPy/ MWCNT/CPE in the concentration range from 0.11 (Pb2+), 0.16 (Cd2+), 0.5, 1, 5, 10, 20, 50, 80, 90, 120, 130, 140–150 μg L−1 for each metal ion. Insert the calibration plot of Pb2+ and Cd2+ versus the concentrations. 5

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

Table 2 Comparison of the analytical performance of Bi-PPy/MWCNT/CPE with some other modified electrodes for the determination of Pb2+ and Cd2+. Sensor

Technique

Deposition Potential (V)

Deposition Time (s)

Linear range (μg L−1) Cd

GR/PANi/SPE Bi/NA/PANi-MES/GCE Bi-MWCNT/EBP-NA/GCE BiF/SWCNHs/SPE SPAN/MCN/GCE ZnO@GR/SPE L-Cys/GR-CS/GCE GSH@Fe3O4/MGCE Bi-PPy/MWCNT/CPE

SWASV SWASV SWASV SWASV SWASV SWASV DPASV SWASV SWASV

−1.2 −1.2 −1.4 −1.2 −1.0 −1.2 −1.1 −1.4 −1.2

720 300 120 150 300 180 120 210 240

2+

1-300 0.1-30 1-50 1-60 5-80 10-200 0.56-67.2 0.5-100 0.16-120

Pb

2+

1-300 0.1-20 1-50 1-60 5-80 10-200 1.04-62.1 0.5-100 0.11-120

Detection limit (μg L−1) Cd

2+

0.1 0.04 0.06 0.2 0.7 0.6 0.12 0.171 0.157

Pb

Ref

2+

0.1 0.05 0.08 0.4 0.2 0.8 0.45 0.182 0.099

[38] [39] [40] [41] [42] [15] [43] [44] This work

GR: graphene, PANi: Polyaniline, SPE: Screen printed electrode, NA: nafion, MES: 2-mercaptoethanesulfonate, GCE: glassy carbon electrode, EBP: emeraldine base polyaniline, BiF: bismuth film, SWCNHs: single-walled carbon nanohorns, SPAN: Self-doped polyaniline nanofibres, MCN: mesoporous carbon nitride, L-Cys: LCysteine, GSH: Glutathione, MGCE: magnetic glassy carbon electrode, sGO: cysteine-functionalized graphene oxide.

detection (LODs) and limit of quantification (LOQs) were determined using the following equations [37]: LOBs = mean

blank

+ 1.645(SD

LODs = LOBs + 1.645(SD

blank)

low concentration sample)

Where: LOBs is the limits of blank, SD is standard deviation (The experimental data of the blank and the concentration of level LODs are given in supporting information Fig. S3) The LOQs may be equivalent to the LODs or it could be at a much higher concentration. Then, the limits of detection of Pb2+ and Cd2+ are respectively of about 0.099 and 0.157 μg L−1, while the limits of quantification are of about 0.1 and 0.16 μg L−1 respectively for Pb2+ and Cd2+. A comparison of the analytical features of Bi-PPy/MWCNT/CPE with other similar modified electrodes reported in the literature for the simultaneous determination of Pb2+ and Cd2+ is listed in the Table 2. It can be concluded that the Bi-PPy/MWCNT/CPE showed a lower limit of detection and a short deposition time than most of the compared electrodes. 3.8. Repeatability, reproducibility and stability

Fig. 6. Effect of interference ions on the detection of 90 μg L−1 Pb2+ and Cd2+ using Bi-PPy/MWCNT/CPE under the optimized experimental conditions.

The repeatability of the method was evaluated for the determination of 90 μg L−1 of Pb2+ and Cd2+ using Bi-PPy/MWCNT/CPE under the optimized experimental conditions. After five successive measurements using the same modified electrode, the calculated relative standard deviation (RSD) for Cd2+ and Pb2+ were of about 1.9 and 2.1% respectively. The reproducibility of the measures of Bi-PPy/MWCNT/CPE was also tested, a series of five electrodes were prepared then applied for the detection of 90 μg L−1 of Pb2+ and Cd2+. The relative standard deviation of the measurements obtained with five prepared electrodes was equal to 2.8 and 3.2% for Cd2+ and Pb2+ respectively. This indicates that a very satisfactory reproducibility was obtained. On the other hand, the stability of the responses of Bi-PPy/MWCNT/CPE over time was also tested. As shown in Fig. S4 it can be seen that the stripping peak currents of Pb2+ and Cd2+ were slightly changed, indicating that the response of the Bi-PPy/MWCNT/CPE is stable over ten days.

which indicating a good selectivity of the Bi-PPy/MWCNT/CPE for the simultaneous detection of Pb2+ and Cd2+. However, in the case of Cu2+ a 1-fold mass ratio was found as the tolerance ratios for the detection of Pb2+ and Cd2+ at 90 μg L−1. This effect is due to the formation of intermetallic compounds as well as competition metal ions for active sites on the surface of the electrode, which leads to a difficult detection of target metal ions [40,45]. Nevertheless, the effect of Cu2+ on stripping analysis of Pb2+ and Cd2+ in water samples containing high levels of Cu2+ could be effectively reduced, without having a detrimental effect on the target metal ions, by addition of 0.1 mM ferrocyanide with stirring during 10 min. This is due to the capacity of ferrocyanide to form a stable copper-ferrocyanide complex [46–48].

3.10. Analysis of real samples

3.9. Interference study

In order to validate and evaluate the efficiency of the proposed method for analysis of Pb2+ and Cd2+ in real samples, the Bi-PPy/ MWCNT/CPE was used to analyze real samples of tap water obtained from Mohammedia (Morocco). Four samples of tap water were prepared and analyzed under the optimized experimental conditions. The results of the first sample indicate the presence of Pb2+ and the absence of obvious responses of Cd2+ as displayed in Fig. 7. Then, to determine the concentration of Pb2+, the sample water was spiked with different

The selectivity of Bi-PPy/MWCNT/CPE for the simultaneous detection of Pb2+ and Cd2+ was investigated in the presence of non-target metal ions. Fig. 6 shows the effect of different interference ions at a 25fold on the detection of 90 μg L−1 of Pb2+ and Cd2+. From the obtained results it can be concluded that the absolute relative change of signal in the presence of different ions interferences varied from 0.40 to 4.88%, 6

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

Fig. 7. Analysis of Pb2+ in a sample of tap water using Bi-PPy/MWCNT/CPE under the optimized experimental conditions.

samples of tap water with very satisfactory results. The present investigation describes an effective and promising application of nanocomposites as sensing materials of trace heavy metal ions.

Table 3 Recovery and relative standard deviation (RSD) of Cd2+ and Pb2+ in the tap water samples using the modified electrode Bi-PPy/MWCNT/CPE (n = 3). Samples

Added (μg L−1, n = 3) Cd

2+

Pb

2+

Found (μg L−1, n = 3) 2+

Cd

*

Tap water 1

0

0

ND

Tap water 2 Tap water 3 Tap water 4

5 10 15

5 10 15

4.92 10.25 14.86

Pb

2+

1.35 ( ± 0.31) 6.25 11.48 17.01

Recovery (%)

RSD (%)

Acknowledgements Cd

2+

Pb

2+

Cd

2+

2+

Pb

–

–

–

–

98.4 102.5 99.06

98.0 101.8 104.4

1.1 2.1 2.3

1.3 1.9 2.1

This work was supported by MESRSFC (Ministère de l'Enseignement Supérieur et de la Recherche Scientifique et de la Formation des cadres Morocco) and CNRST (Centre National pour la Recherche Scientifique et Technique - Morocco) (Project number PPR/2015/72). The authors also acknowledge Mrs Françoise Pillier for FEG-SEM analysis, and the Erasmus Mundus program EMMAG. Appendix A. Supplementary data

* ND: Not detected.

concentration of Pb2+ which are 5, 10, 15, 20 and 25 μg L−1. The concentration of Pb2+ in the analyzed sample was of about 1.35 μg L−1. In order to further study the applicability of Bi-PPy/MWCNT/CPE for the simultaneous determination of Pb2+ and Cd2+ the recovery evaluation was realized. Three samples of the same tap water were spiked with different concentration of Pb2+ and Cd2+, the results are shown in Table 3. It can be seen that the recoveries were found in the range of 98.4–102.5% and 98–104.4% for Cd2+ and Pb2+ respectively. These results showed that the Bi-PPy/MWCNT/CPE has a good recovery, suggesting the great application potential in real samples.

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.synthmet.2019.04. 011. References [1] J.O. Duruibe, M.O.C. Ogwuegbu, J.N. Egwurugwu, Heavy metal pollution and human biotoxic effects, Int. J. Phys. Sci. 2 (2007) 112–118. [2] S.J.S. Flora, S. Agrawal, Chapter 31 - arsenic, cadmium, and lead, in: R.C. Gupta (Ed.), Reprod. Dev. Toxicol, second ed., Academic Press, 2017, pp. 537–566. [3] V. Kazantzi, A. Kabir, K.G. Furton, A. Anthemidis, Fabric fiber sorbent extraction for on-line toxic metal determination by atomic absorption spectrometry: determination of lead and cadmium in energy and soft drinks, Microchem. J. 137 (2018) 285–291. [4] N. Zhang, K. Shen, X. Yang, Z. Li, T. Zhou, Y. Zhang, Q. Sheng, J. Zheng, Simultaneous determination of arsenic, cadmium and lead in plant foods by ICP-MS combined with automated focused infrared ashing and cold trap, Food Chem. 264 (2018) 462–470. [5] Y. Yang, J. Cheng, B. Wang, Y. Guo, X. Dong, J. Zhao, An amino-modified metalorganic framework (type UiO-66-NH2) loaded with cadmium(II) and lead(II) ions for simultaneous electrochemical immunosensing of triazophos and thiacloprid, Microchim. Acta. 186 (2019) 101. [6] P. Hashemi, H. Bagheri, A. Afkhami, Y.H. Ardakani, T. Madrakian, Fabrication of a novel aptasensor based on three-dimensional reduced graphene oxide/polyaniline/ gold nanoparticle composite as a novel platform for high sensitive and specific cocaine detection, Anal. Chim. Acta 996 (2017) 10–19. [7] M.A. Deshmukh, H.K. Patil, G.A. Bodkhe, M. Yasuzawa, P. Koinkar, A. Ramanaviciene, M.D. Shirsat, A. Ramanavicius, EDTA-modified PANI/SWNTs nanocomposite for differential pulse voltammetry based determination of Cu(II) ions, Sens. Actuators B Chem. 260 (2018) 331–338. [8] Y. Song, C. Bian, J. Hu, Y. Li, J. Tong, J. Sun, G. Gao, S. Xia, Porous polypyrrole/ graphene oxide functionalized with carboxyl composite for electrochemical sensor

4. Conclusion In this study, the carbon paste electrode was successfully modified with a novel nanocomposite of Bi-PPy/MWCNT using an easy approach. The structural and electrochemical characterizations of the nanocomposite PPy/MWCNT have shown good electrical properties and a large active surface area. Using square wave voltammetry (SWV) in the presence of Bi3+ and under the optimum experimental conditions, the Bi-PPy/MWCNT/CPE showed good analytical performances for the simultaneous determination of traces Pb2+ and Cd2+, with a very low limit detection of about 99 and 157 ng L−1 respectively for Pb2+ and Cd2+. In addition, a good repeatability, reproducibility, stability and selectivity were obtained. The Bi-PPy/MWCNT/CPE was successfully applied for the determination of Pb2+ and Cd2+ in real 7

Synthetic Metals 253 (2019) 1–8

L. Oularbi, et al.

[29] M. Deng, X. Yang, M. Silke, W. Qiu, M. Xu, G. Borghs, H. Chen, Electrochemical deposition of polypyrrole/graphene oxide composite on microelectrodes towards tuning the electrochemical properties of neural probes, Sens. Actuators B Chem. 158 (2011) 176–184. [30] J. Mondal, M. Marandi, J. Kozlova, M. Merisalu, A. Niilisk, V. Sammelselg, Protection and functionalizing of stainless steel surface by Graphene OxidePolypyrrole composite coating, J. Chem. Chem. Eng. 8 (2014) 786–793. [31] J.N. Barisci, G.G. Wallace, R.H. Baughman, Electrochemical quartz crystal microbalance studies of single-wall carbon nanotubes in aqueous and non-aqueous solutions, Electrochim. Acta 46 (2000) 509–517. [32] H.D. Vu, L.-H. Nguyen, T.D. Nguyen, H.B. Nguyen, T.L. Nguyen, D.L. Tran, Anodic stripping voltammetric determination of Cd2+ and Pb2+ using interpenetrated MWCNT/P1,5-DAN as an enhanced sensing interface, Ionics 21 (2014) 571–578. [33] G.Z. Chen, M.S.P. Shaffer, D. Coleby, G. Dixon, W. Zhou, D.J. Fray, A.H. Windle, Carbon Nanotube, Polypyrrole composites: coating and doping, Adv. Mater. 12 (2000) 522–526. [34] H.N.M.E. Mahmud, A.K.O. Huq, R. binti Yahya, The removal of heavy metal ions from wastewater/aqueous solution using polypyrrole-based adsorbents: a review, RSC Adv. 6 (2016) 14778–14791. [35] Y. Kong, J. Wei, Z. Wang, T. Sun, C. Yao, Z. Chen, Heavy metals removal from solution by polyaniline/palygorskite composite, J. Appl. Polym. Sci. 122 (2011) 2054–2059. [36] J. Wang, Stripping analysis at bismuth electrodes: a review, Electroanalysis. 17 (2005) 1341–1346. [37] D.A. Armbruster, T. Pry, Limit of blank, limit of detection and limit of quantitation, Clin. Biochem. Rev. 29 (2008) S49–S52. [38] N. Ruecha, N. Rodthongkum, D.M. Cate, J. Volckens, O. Chailapakul, C.S. Henry, Sensitive electrochemical sensor using a graphene–polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II), Anal. Chim. Acta 874 (2015) 40–48. [39] L. Chen, Z. Su, X. He, Y. Liu, C. Qin, Y. Zhou, Z. Li, L. Wang, Q. Xie, S. Yao, Square wave anodic stripping voltammetric determination of Cd and Pb ions at a Bi/ Nafion/thiolated polyaniline/glassy carbon electrode, Electrochem. commun. 15 (2012) 34–37. [40] G. Zhao, Y. Yin, H. Wang, G. Liu, Z. Wang, Sensitive stripping voltammetric determination of Cd(II) and Pb(II) by a Bi/multi-walled carbon nanotube-emeraldine base polyaniline-Nafion composite modified glassy carbon electrode, Electrochim. Acta 220 (2016) 267–275. [41] Y. Yao, H. Wu, J. Ping, Simultaneous determination of Cd(II) and Pb(II) ions in honey and milk samples using a single-walled carbon nanohorns modified screenprinted electrochemical sensor, Food Chem. 274 (2019) 8–15. [42] C. Zhang, Y. Zhou, L. Tang, G. Zeng, J. Zhang, B. Peng, X. Xie, C. Lai, B. Long, J. Zhu, Determination of Cd2+ and Pb2+ based on mesoporous carbon nitride/ self-doped polyaniline nanofibers and square wave anodic stripping voltammetry, Nanomaterials 6 (2016) 7. [43] W. Zhou, C. Li, C. Sun, X. Yang, Simultaneously determination of trace Cd2+ and Pb2+ based on l-cysteine/graphene modified glassy carbon electrode, Food Chem. 192 (2016) 351–357. [44] M. Baghayeri, A. Amiri, B. Maleki, Z. Alizadeh, O. Reiser, A simple approach for simultaneous detection of cadmium(II) and lead(II) based on glutathione coated magnetic nanoparticles as a highly selective electrochemical probe, Sens. Actuators B Chem. 273 (2018) 1442–1450. [45] T.D. Nguyen, T.T.H. Dang, H. Thai, L.H. Nguyen, D.L. Tran, B. Piro, M.C. Pham, One-step electrosynthesis of poly(1,5-diaminonaphthalene)/graphene nanocomposite as platform for lead detection in water, Electroanalysis. 28 (2016) 1907–1913. [46] N. Promphet, P. Rattanarat, R. Rangkupan, O. Chailapakul, N. Rodthongkum, An electrochemical sensor based on graphene/polyaniline/polystyrene nanoporous fibers modified electrode for simultaneous determination of lead and cadmium, Sens. Actuators B Chem. 207 (Part A) (2015) 526–534. [47] G. Zhao, H. Wang, G. Liu, Z. Wang, J. Cheng, Simultaneous determination of trace Cd(II) and Pb(II) based on Bi/Nafion/reduced graphene oxide-gold nanoparticle nanocomposite film-modified glassy carbon electrode by one-step electrodeposition, Ionics 23 (2017) 767–777. [48] K. Crowley, J. Cassidy, Trace analysis of lead at a nafion-modified electrode using square-wave anodic stripping voltammetry, Electroanalysis 14 (2002) 1077–1082.

of trace cadmium (II), J. Electrochem. Soc. 166 (2019) B95–B102. [9] N. Hilali, A. Ghanam, H. Mohammadi, A. Amine, J.J. García‐Guzmán, L. Cubillana‐Aguilera, J.M. Palacios‐Santander, Comparison between modified and unmodified carbon paste electrodes for hexavalent chromium determination, Electroanalysis 30 (2018) 2750–2759. [10] A. Waheed, M. Mansha, N. Ullah, Nanomaterials-based electrochemical detection of heavy metals in water: current status, challenges and future direction, TrAC Trends Anal. Chem. 105 (2018) 37–51. [11] N. Baig, M. Sajid, T.A. Saleh, Recent trends in nanomaterial-modified electrodes for electroanalytical applications, TrAC Trends Anal. Chem. 111 (2019) 47–61. [12] S. Kumar, M. Sarita, N. Nehra, K. Dilbaghi, K.-H. Tankeshwar, Kim, Recent advances and remaining challenges for polymeric nanocomposites in healthcare applications, Prog. Polym. Sci. 80 (2018) 1–38. [13] L. Oularbi, M. Turmine, M. El Rhazi, Electrochemical determination of traces lead ions using a new nanocomposite of polypyrrole/carbon nanofibers, J. Solid State Electrochem. 21 (2017) 3289–3300. [14] M. El Rhazi, S. Majid, M. Elbasri, F.E. Salih, L. Oularbi, K. Lafdi, Recent progress in nanocomposites based on conducting polymer: application as electrochemical sensors, Int. Nano Lett. 8 (2018) 79–99. [15] J. Yukird, P. Kongsittikul, J. Qin, O. Chailapakul, N. Rodthongkum, ZnO@graphene nanocomposite modified electrode for sensitive and simultaneous detection of Cd (II) and Pb (II), Synth. Met. 245 (2018) 251–259. [16] Y. Lu, X. Liang, C. Niyungeko, J. Zhou, J. Xu, G. Tian, A review of the identification and detection of heavy metal ions in the environment by voltammetry, Talanta 178 (2018) 324–338. [17] M.A. Deshmukh, G.A. Bodkhe, S. Shirsat, A. Ramanavicius, M.D. Shirsat, Nanocomposite platform based on EDTA modified Ppy/SWNTs for the sensing of Pb (II) ions by electrochemical method, Front. Chem. 6 (2018). [18] W. Wu, M. Jia, Z. Wang, W. Zhang, Q. Zhang, G. Liu, Z. Zhang, P. Li, Simultaneous voltammetric determination of cadmium(II), lead(II), mercury(II), zinc(II), and copper(II) using a glassy carbon electrode modified with magnetite (Fe3O4) nanoparticles and fluorinated multiwalled carbon nanotubes, Microchim. Acta 186 (2019) 97. [19] G. Zhao, G. Liu, Electrochemical deposition of gold nanoparticles on reduced graphene oxide by fast scan cyclic voltammetry for the sensitive determination of As (III), Nanomaterials 9 (2019) 41. [20] F.E. Salih, A. Ouarzane, M. El Rhazi, Electrochemical detection of lead (II) at bismuth/Poly(1,8-diaminonaphthalene) modified carbon paste electrode, Arab. J. Chem. 10 (2017) 596–603. [21] X. Xuan, J.Y. Park, A miniaturized and flexible cadmium and lead ion detection sensor based on micro-patterned reduced graphene oxide/carbon nanotube/bismuth composite electrodes, Sens. Actuators B Chem. 255 (2018) 1220–1227. [22] Z. Lu, J. Zhang, W. Dai, X. Lin, J. Ye, J. Ye, A screen-printed carbon electrode modified with a bismuth film and gold nanoparticles for simultaneous stripping voltammetric determination of Zn(II), Pb(II) and Cu(II), Microchim. Acta 184 (2017) 4731–4740. [23] H. Wang, G. Zhao, Y. Yin, Z. Wang, G. Liu, Screen-printed electrode modified by bismuth /Fe3O4 Nanoparticle/Ionic liquid composite using internal standard normalization for accurate determination of Cd(II) in soil, Sensors 18 (2017) 6. [24] F. Tseliou, A. Avgeropoulos, P. Falaras, M.I. Prodromidis, Low dimensional Bi2Te3graphene oxide hybrid film-modified electrodes for ultra-sensitive stripping voltammetric detection of Pb(II) and Cd(II), Electrochim. Acta 231 (2017) 230–237. [25] D. Riman, D. Jirovsky, J. Hrbac, M.I. Prodromidis, Green and facile electrode modification by spark discharge: Bismuth oxide-screen printed electrodes for the screening of ultra-trace Cd(II) and Pb(II), Electrochem. Commun. 50 (2015) 20–23. [26] N. Jeromiyas, E. Elaiyappillai, A.S. Kumar, S.-T. Huang, V. Mani, Bismuth nanoparticles decorated graphenated carbon nanotubes modified screen-printed electrode for mercury detection, J. Taiwan Inst. Chem. Eng. 95 (2019) 466–474. [27] J.-H. Hwang, X. Wang, D. Zhao, M.M. Rex, H.J. Cho, W.H. Lee, A novel nanoporous bismuth electrode sensor for in situ heavy metal detection, Electrochim. Acta 298 (2019) 440–448. [28] E.T. Mombeshora, R. Simoyi, V.O. Nyamori, P.G. Ndungu, Multiwalled carbon nanotube-titania nanocomposites: understanding nano-structural parameters and functionality in dye-sensitized solar cells, South Afr. J. Chem. Eng. 68 (2015) 153–164.

8