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Article

Chitosan and Metal Oxide Functionalized Chitosan as Efficient Sensors for Lead (II) Detection in Wastewater

by
Walid Boultif
1,
Charif Dehchar
2,3,
Youghourta Belhocine
1,
Emna Zouaoui
1,*,
Seyfeddine Rahali
4,
Salah Eddine Zouari
3,
Najoua Sbei
5 and
Mahamadou Seydou
6,*
1
Laboratory of Catalysis, Bioprocess and Environment, Department of Process Engineering, Faculty of Technology, University of 20 August 1955, Skikda 21000, Algeria
2
Laboratoire Croissance et Caractérisation de Nouveaux Semi-Conducteurs, Université Ferhat Abbas, Sétif-1, Setif 19000, Algeria
3
Department of Process Engineering, Faculty of Technology, University of 20 August 1955, Skikda 21000, Algeria
4
Department of Chemistry, College of Science and Arts, Qassim University, Ar Rass 52719, Saudi Arabia
5
Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein Leopoldshafen, 76344 Karlsruhe, Germany
6
Université Paris Cité, CNRS, ITODYS, F-75013 Paris, France
*
Authors to whom correspondence should be addressed.
Separations 2023, 10(9), 479; https://doi.org/10.3390/separations10090479
Submission received: 30 July 2023 / Revised: 27 August 2023 / Accepted: 30 August 2023 / Published: 31 August 2023
(This article belongs to the Special Issue Development of Materials for Separation and Detection of Metals and Chemicals)
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Abstract

:
The work presented in this paper describes the preparation and the electrochemical application of functionalized chitosan-entrapped carbon paste electrodes (CH/CPE) for lead ions (Pb2+) detection in industrial wastewater. The chitosan was first functionalized using TiO2 and CuO, which were both metal oxides that were obtained by extracting it from waste products derived from shrimp shells. The analytical performance of the as-prepared electrodes, CH/CPE, TiO2-CH/CPE, and NiO-CH/CPE, for the detection of lead (II) was examined using electrochemical impedance spectroscopy (EIS) technique in the 0.1 M KNO3 electrolyte solution. The effect of experimental conditions, including polarization potential, frequency, and pH, are optimized to maximize the sensitivity of the measurements. The developed impedimetric sensors provided a linear response over a concentration range of 10−6 to 10−4 M with a detection limit of 3.10−7 M based on S/N = 3. The DFT computational analysis demonstrated that chitosan biopolymer possesses the ability to adsorb Pb (II) ions that are present in wastewater. Chitosan and the derivatives of chitosan, have the potential to remove heavy metals from industrial effluent in a manner that is both economical and eco-friendly to the environment. Chitosan is a biopolymer that is abundantly renewable.

1. Introduction

Lead is a highly toxic metal and a harmful pollutant that affects public health and the environment [1,2,3,4,5]. Due to its toxicity even at low levels, the usage of lead was prohibited or regulated in many industries. However, in some countries, the continued use of lead in paints [6,7], pigments [8], gasoline [9,10], ammunition [11,12], ceramic glazes [13,14], aviation fuel [15], batteries [16], mining [17], smelting [18], and recycling activities [19] is still representing an important environmental pollution and health issue.
As an example, Fe3+ plays a key role in several biochemical reactions and is considered a vital element for survival. However, a high accumulation level of Fe3+ could result in liver damage, heart diseases, and diabetes.
Indeed, significant amounts of heavy metals such as mercury (Hg) would lead to renal failure, hearing damage, and nerve disorders in the human body. Pb and cadmium (Cd) enter the environment through the metallurgical industry [20,21], burning of fossil fuels [22], and wastewater releases [23,24]. Lead is not biodegradable and resists corrosion [25], leading to its accumulation in air, water, and soil [26]; therefore, the development of reliable methods to detect and remove lead is of utmost importance [27,28,29,30,31,32,33,34]. However, the direct detection in the samples of trace-heavy metals such as lead (Pb) and cadmium (Cd) is a difficult task, mainly due to their very low concentrations, often below the detection limit of available techniques [35]; including spectroscopic methods, such as atomic emission spectroscopy (AES), atomic absorption spectroscopy (AAS), chromatography methods, etc. However, these methods have limitations for their widespread applications due to their high cost, time consumption, and sophisticated operations.
Nowadays, the development of advanced technologies, abundant unique sensing platforms based on MS, colorimetry, electrochemistry, surface-enhanced Raman scattering (SERS), and fluorescence have been reported to detect trace metal ions.
The reported results showed that MS and SERS with ultrahigh sensitivity gave exact molecular information. The colorimetric and fluorescent sensors allow simply and intuitively observing the changes generated by the target metal ions. Furthermore, electrochemical sensors are suitable for simultaneous detection of various metal ions due to their distinctive and fast responses to different metal ions. Moreover, in order to enhance the sensitivity and selectivity of metal–ion sensors, nanomaterials have been extensively applied in sensor constructions, such as noble metal nanoparticles, porous nanomaterials, semiconductors, etc.
In recent decades, the use of metal oxide has been grown in different applications; for example, the perovskite oxides have been used as a catalyst to produce green hydrogen, which was reported by Daqin Guan and co-workers [36]. Similarly, Guan et al. reported that the tensile-strained RuO2 has been used as a catalyst for the proton-exchange membrane in water electrolysis [37]. Recently in 2023, transition metal oxides (TMOs) have been used in Li-S battery application which contribute to the high-rate and long-durability of the battery [38].
The monitoring of lead contamination levels in wastewaters is crucial for the effective control of lead pollution [38]. The World Health Organization (WHO) recommends maintaining the concentration of lead as low as possible (the safe limit of Pb content in wastewater is 0.01 ppm) [39]. Several methods have been developed to remove lead from wastewater, such as ion exchange [40,41,42], adsorption [43,44,45,46,47], reverse osmosis [48,49,50], precipitation [51,52,53], electrocoagulation [54,55,56,57,58], and electrodialysis [59,60].
The detection of lead in wastewater can be achieved using a variety of analytical devices such as chromatographs and spectrophotometers [61,62,63], but they are generally complex, expensive, and often difficult to use—these disadvantages show the need for an alternative approach to classical instruments [64,65].
Chemical sensors represent a powerful analytical tool for simple, inexpensive, reliable, rapid, and selective detection of heavy metals [66,67,68,69,70]. Currently, chemical sensors are widely used in various applications that include biomedical instrumentation, detection of industrial emissions, electrochemical sensing devices, environmental pollution, and water quality monitoring [71,72].
Particularly in recent times, there has been a lot of interest in sensors that are based on electrochemistry because of their potential as on-site environmental pollution monitors. The creation of an electrochemical sensor needs the optimization of two different components: a selective part and a transducer system. Among different transduction techniques, electrochemical impedance spectroscopy is considered as one of the most versatile and powerful methods for determining the electrical properties occurring at the sensor–analyte interface [73,74,75].
The development of theoretical approaches used to investigate the interaction properties for the detection of environmental pollution has been discussed in a series of papers. Currently, the density–functional theory (DFT) is largely used in computational approaches to confirm and complete experimental findings, and specifically to describe the interaction mechanism between the pollutant and the developed system.
In this study, we investigated the behavior of developed electrochemical sensors based on chitosan and functionalized chitosan by TiO2 and NiO for the detection of lead ions found in industrial wastewater. Chitosan and its derivatives, as biodegradable and non-toxic natural polymers, may exhibit interesting sensing properties.

2. Materials and Methods

2.1. Chemicals and Reagents

Chitosan is extracted from shrimp Parapenaeuslongirostris shells (Figure 1a), collected from local fish restaurants in Skikda City (Algeria), by a chemical process following the protocol of Benhabiles et al. [76]. Chemicals used for the chitosan preparation process are hydrochloric acid (HCl 36%), sodium hydroxide (NaOH, 99%), and hydrogen peroxide (H2O2, 30%) (purchased from Prolabo). Acetic acid (CH3CO2H), tin oxide (TiO2), and nickel (II) oxide (purchased from Sigma–Aldrich) were used for the functionalization of chitosan. In order to make the carbon pastes, high-quality graphite powder with a mesh size of 325, supplied by Asbury Carbons, and paraffin oil with a purity level of 99% were required as ingredients. There was no treatment of any of the compounds before usage. In each of the tests, distilled water was utilized throughout the preparation and analysis processes.

2.2. Preparation of Chitosan

The shrimp wastes were prepared for use by first having their legs and antennae removed and were then washed multiple times in warm water (70 °C) to eliminate any organic residues, and at last were air-dried for an entire night (Figure 1a). In the end, the waste samples were reduced to a powdery consistency by being ground in a porcelain mortar and pestle (Figure 1b).
The preparation process involves four steps: first, deproteinization is achieved in sodium hydroxide (2.5 N, NaOH) solution at a solvent to solid ratio (v/w) of 10/1 mL/g at 75 °C during 6 h. The product is then decanted under vacuum, washed thoroughly with distilled water until the pH reaches a neutral value (pH = 7) and is oven-dried at 80 °C for 3 h. The second step consists of demineralization by acid treatment to eliminate calcium carbonate and calcium phosphate naturally present in shrimp shells [77]. Hydrochloric acid of 1.7 N is used with a solvent to solid ratio of 10/1 mL/g at ambient temperature during the 6 h. The final product, chitin, is given a quick rinse in running water before being dried in an oven at 80 degrees Celsius for 3 h. The subsequent procedure is referred to as “decolorization,” and its purpose is to remove the pigments from the chitin using reagents, such as ether, ethanol, sodium hypochlorite, or hydrogen peroxide. In this study, a 30% concentration of hydrogen peroxide of was used at ambient temperature for 10 min. After that, the samples were washed thoroughly with tap water to remove any residual impurities and oven-dried at 80 °C for 3 h. The last step was deacetylation by concentrated sodium hydroxide (50%) solution with a solvent to solid ratio of 10/1 mL/g at ambient temperature for 48 h. By removing the acetyl group from the chitin in this stage (Figure 2), the goal was to transform the chitin into chitosan. Chitosan, the product that was obtained, was put through a filter, washed with distilled water until the filtrate became neutral, and then oven-dried at a temperature of 50 °C overnight.

2.3. Preparation of Functionalized Chitosan

Functionalization of chitosan aims to improve its properties, including electronic, mechanical, and electrochemical properties, to develop new materials for diverse applications [78]. In general, this functionalization is achieved by acid treatments, as chitosan is only soluble in acidic solutions and does not disperse easily in water [79]. In this study, chitosan was placed in 200 mL of 5% (v/v) acetic acid solution for 24 h to form a homogenous suspension. The experiments were carried out at room temperature (~22 °C) with constant stirring (200 rpm). Next, 10% (w/v) of active substance X (X = TiO2, NiO) was gradually added to mix with the suspension under constant stirring. Duration of the experiment was 24 h at ambient temperature. The obtained mixture was then washed several times by distilled water, filtered under vacuum, and dried in an oven at 100 °C.
The choice of the two metal oxides (TiO2 and NiO) for functionalizing chitosan was based on their distinct properties, such as binding affinity with surfaces capable of undergoing complexation, ion exchange, and electrostatic interactions with lead ions. Furthermore, their catalytic abilities enable them to catalyze redox reactions involving lead ions, leading to amplified signals in electrochemical sensing methods. Additionally, their biocompatibility and chemical stability make them suitable for integration with chitosan without compromising the composite’s overall properties.

2.4. Preparation of Chitosan Modified Electrodes

A carbon paste electrode (CPE) was chosen to prepare our functionalized chitosan-based electrodes, as it is simple to manufacture and suitable for preparing modified electrodes with admixtures of different substances; thus, giving the material certain characteristic properties [80]. The electrodes were prepared by mixing a desired weight (20%) of functionalized chitosan and 70% of selected carbon material (graphite powder) with paraffin oil, as a binder, using an agate mortar and pestle for 30 min until a homogeneous mixture was obtained. This ratio was carefully chosen to achieve an optimal balance between the enhanced binding properties of functionalized chitosan and the electrical conductivity of graphite powder.
The synthesized mixture was then introduced into a PVC tube of an appropriate length of 12 cm. Electrical contact was established via passing a thin copper wire from the opposite end through the paste. The outer surfaces of the electrodes were polished with alumina to remove the excess of solidified material and achieve a flat surface. After the electrodes were polished, they were thoroughly rinsed with distilled water and air-dried.

2.5. Fourier Transforms Infrared Spectroscopy (FTIR)

The degree of N-deacetylation (DD) of chitosan samples was determined by the method of Sabnis and Block [81] using FTIR spectroscopy. The spectra were obtained using a Perkin Elmer 1600 spectrometer from the 4000 to 400 cm−1 frequency range. The DD was calculated using the equation proposed by Baxter et al. [82]:
DD = 100 − [100 × (A1655/A3450)/1.33]
where DD is N-deacetylation degree and A1655 and A3450 are the absorbance band maxima of the chitosan infrared spectrum at 1655 cm−1 of the amide-I band and 3450 cm−1 of the hydroxyl band, respectively. The factor 1.33 denotes the value of the ratio A1655/A3450 for fully N-acetylated chitosan [83,84].

2.6. Electrochemical Measurements

Electrochemical impedance spectroscopy (EIS) measurements for the detection of lead (II) on the prepared chitosan-based electrodes were performed in a conventional three-electrode system at room temperature. A platinum (Pt) wire was used as counter electrode (CE), and a saturated calomel electrode (SCE) was used as the reference electrode (RE). All potentials are referred to this electrode. A Voltalab PGZ 301 potentiostat was used to run the experiments.
The working electrode (WE) was incubated for 10 min; then, it was washed and placed in the electrochemical cell containing 0.1 M potassium nitrate (KNO3) as the supporting electrolyte.

3. Results and Discussion

3.1. FTIR Analysis

FTIR is the most suitable technique for a quick and simple characterization of DD of chitosan. This parameter is extremely important as it influences the properties of the macromolecular chains of the polymers and their behavior in solution, namely the solubility of the chitosan, the flexibility of the macromolecular chains, and the polymer conformation. Figure 3 depicts the infrared spectrum of the chitosan sample. It displays a series of bands: the peak noticed at 1555 cm−1 corresponds to N–H bending of the secondary amide II band of –CONH– whereas the amide I band resulting from hydrogen and hydroxyl interactions (due to the deacetylation of chitin) is observed at 1655 cm−1. Small peaks around 2900 cm−1 are assigned to the –CH2– and –CH3 groups. –OH, stretching vibrations of water, and hydroxyls as well as –NH stretching vibrations of free amino groups, are observed at 3100–3500 cm−1. Using the Baxter equation (Equation (1)), the DD of the produced chitosan was found to be 53.33%.

3.2. Detection of Pb (II)

The electrochemical impedance spectroscopy (EIS) technique was used to investigate the electrochemical detection of lead. The optimal experimental conditions, in terms of polarization potential, frequency, and pH, were first determined. Indeed, these parameters are known to have a significant effect on the response of impedimetric sensors.
Figure 4a shows the impedance spectra in the Nyquist plots of the CH/CPE electrode at different potentials (−100, −200, and −400 mV) over a range of frequency from 0.1 Hz to 100 kHz and a sinusoidal excitation signal amplitude of 10 mV. At negative voltages, there is a clear decrease in total impedance. The Warburg straight line at the low-frequency side is reduced as the potential decreases, disappearing at −400 mV and being replaced by a well-defined semicircle. This means that at this potential, the charge–transfer resistance is lower and mass transport has no significant effect on the electrode response. A very similar behavior has been obtained with the TiO2-CH/CPE and NiO-CH/CPE electrodes; hence, the polarization potential of −400 mV and frequency range from 0.1 Hz to 100 kHz were retained for the rest of this study.
Figure 4b shows impedance spectra of the CH/CPE electrode recorded at different pH values: 2, 3, 4, 6 and 10. The pH was adjusted by adding KOH and HCl to the electrolyte. As can be seen, the electrode showed very different responses depending on the pH value. The best response, in terms of lower charge–transfer resistance, was obtained at pH = 6; therefore, this value of pH was chosen for further study.
The electrochemical response of the CH/CPE, TiO2-CH/CPE and NiO-CH/CPE electrodes for the detection of lead ions (Pb2+) was examined using EIS measurements in 0.1 M KNO3 electrolyte in the presence of different concentrations of the target analyte.
Figure 5a–c show the Nyquist plots of the impedance spectra corresponding to the three electrodes. A sharp decrease in total impedance, for all three cases, is clearly seen after addition of Pb2+ ions, indicating a good sensitivity of the developed electrodes to changes in analyte concentration.
The impedance spectra were fitted using the equivalent circuit shown in Figure 5d. The given model is a combination of three parts. The first part is a series resistance of the electrolyte solution, Rs. The second part at high frequency sides, which is attributed to the electrode/film interface, is reproduced by a film capacitance, Qf, and a film resistance, Rf. The third part at the low frequency, which is attributed to the film/electrolyte interface, is reproduced by a charge–transfer resistance, Rct, in parallel with a double-layer capacitance, Qdl.
To evaluate the performance of the electrodes for lead ions determination, the evolution of charge–transfer resistance, Rct, is used. The fitted values of Rct are summarized in Table 1.
Table 1 reveals that the Rct gradually reduces as the concentration of Pb2+ ions in the solution increases; hence, this suggests that the charge–transfer is improved when there is a larger concentration of Pb2+ ions in the solution. This can be seen for all three electrodes. In fact, the current flow increases as the ionic concentration rises, while the charge–transfer resistance falls. This is because there are more ions participating in the electric conduction process as the ionic concentration rises. The sensing performance of the electrodes is figured out by first plotting calibration curves, which are performed with the help of the correlation that exists between the amount of the ions present in the solution and the charge–transfer resistance. The calibration curves of the sensors, shown in Figure 6, present the variation of charge–transfer resistance, Rct0−Rct, versus the added concentration of Pb2+ ions where Rct0 is the charge–transfer resistance of the electrolyte solution without Pb2+ ions.
These results indicate that functionalized chitosan demonstrates improved performance in terms of –charge–transfer compared to non-functionalized chitosan. This enhancement becomes particularly pronounced in the low lead ion concentration range (<10−5 M) for TiO2, while the influence of NiO addition can be observed across all tested concentration ranges.
The limit of detection (LOD) was determined from the formula 3σ/s where σ is the standard deviation of the intercept and s is the slope of the calibration curve.
In order to evaluate the analytical performance of the impedimetric sensors that were constructed, a comparison was made with the analytical performance of other sensors from the published literature that were utilized for the measurement of Pb2+ ions. As can be observed in Table 2, not only did our sensors have a straightforward preparation procedure and a low cost of manufacture, but they also displayed a wide linear range and a low detection limit.

3.3. Selectivity Study

The selectivity of the developed impedimetric sensors toward Pb2+ ions was tested in the presence of Cd2+ interfering ions at different concentrations. The typical Nyquist plots of impedance spectra of Pb2+ solution in the absence and presence of Cd2+ are shown in Figure 7a–c.
The impedance spectra of all three electrodes in the presence of Cd2+ ions did not show any noticeable change in responses, which indicates that the electrodes have a good selectivity to the analyte of interest.

3.4. DFT-D3 Calculations of Intermolecular Interactions

We carried out a computer analysis making use of DFT calculations in order to verify the outcomes that were achieved. Using the periodic DFT approach that is included in the Vienna Ab initio Simulation Package (VASP 5.4.1), an investigation into the selectivity of chitosan for the adsorption of Pb2+ and Cd2+ ions was carried out. [90]. The generalized gradient approximation (GGA) was used with the Perdew−Burke−Ernzerhof (PBE) function [91]. The cutoff energy for the plane wave basis set used in this study is 500 eV. The convergence criteria for the geometry optimization were 2.0 × 10−4 Å for maximum displacement and 0.05 eV/Å for maximum force. The Monkhorst−Pack scheme is used to generate a grid of (3 × 3 × 1) k-points. The dispersion effect is added using the Grimme approach [92]. The unit cell used in this study consists of 12 carbon, 8 oxygen, 22 hydrogen and 2 nitrogen atoms (Figure 8a). The slab model was employed where the vacuum size of 30 Å was set along the z-axis to avoid the heavy metal interacting with its nearby images.
The different possible adsorption sites of lead and cadmium cations were optimized. The more stable optimized structures are presented in Figure 8b,c. The interaction energy (ΔEi) were then calculated using the following equation:
ΔEi = EMC2+ − (EC + EM2+)
where EMC2+ is the total energy of the heavy metal cations adsorbed on chitosan molecule, EC is the total energy of chitosan, and EM2+ is the energy of isolated cations. Therefore, negative interaction energy suggest that the adsorption process is exothermic, and that the detection of metal cations leads to stable configurations. On the other hand, positive adsorption energy suggest that unstable configurations may emerge from the detection of metal cations. Figure 8b,c present the geometries that are the most stable for the various complexes formed by lead and cadmium ions that are adsorbed on chitosan, along with the energy that are associated with those geometries. Data gathered in Figure 8 indicate that the Pb2+/chitosan complexation is an exothermic process, as calculated adsorption energy is negative (−91.41 kJ/mol), and that the interaction with Cd2+ is unfavorable, as the interaction energy is positive (107.19 kJ/mol). Therefore, the chitosan is only capable of adsorbing lead ions (Pb2+) when exposed to wastewater that also includes cadmium.

4. Conclusions

An environmentally friendly method that is based on the valorization of chitosan recovered from discarded shrimp shells has enabled the development of a straightforward and economical method for the fabrication of impedimetric sensors for the detection of the lead ions Pb2+. In this study, we demonstrated that the extracted chitosan could be functionalized with various metal oxides (TiO2 and NiO), which would then result in the production of active materials. In addition, we demonstrated that electrochemical impedance spectroscopy is a method that is both suitable and effective for the analytical sensing of lead (II) ions, even at extremely low concentrations. The results of the DFT show that there is a powerful contact between the lead ion and the nitrogen atom of the chitosan molecule. This association has an adsorption bond length of 2.57 Å and an adsorption energy of −91.41 kJ/mol. The prepared chitosan and functionalized chitosan-based electrodes displayed good analytical performance as impedimetric sensors with a large linear range (10−6–10−4 M) and low limit of detection (3.10−7 M); hence, they look promising for wastewater monitoring applications.

Author Contributions

Conceptualization, E.Z.; methodology, C.D. and W.B.; software, S.R. and C.D.; validation, Y.B., E.Z., N.S. and M.S.; formal analysis, S.E.Z., W.B. and C.D.; investigation, Y.B., W.B., C.D., M.S., N.S. and S.R.; resources, S.E.Z.; data curation, W.B., C.D., Y.B. and S.R.; writing—original draft preparation, C.D., Y.B., S.R. and W.B.; writing—review and editing, E.Z. and M.S.; visualization, C.D. and S.R.; supervision, E.Z., Y.B. and C.D.; project administration, E.Z. and W.B.; funding acquisition, M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

Quantum chemical calculations were performed using HPC resources from GENCI- [CCRT/CINES/IDRIS] (Grant 2020[A0140807006]).

Conflicts of Interest

The authors declare no conflict of interest.

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Separations 10 00479 g001
Figure 1. Shrimp of Parapenaeuslongirostris: (a) shells and (b) powder.
Figure 1. Shrimp of Parapenaeuslongirostris: (a) shells and (b) powder.
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Figure 2. Conversion of chitin to chitosan by alkaline deacetylation.
Figure 2. Conversion of chitin to chitosan by alkaline deacetylation.
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Figure 3. FTIR spectrum of prepared chitosan.
Figure 3. FTIR spectrum of prepared chitosan.
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Figure 4. Impedance spectra in Nyquist representation of CH/CPE electrode in 0.1 M KNO3 electrolyte: (a) at different polarization potentials and (b) at different pH values.
Figure 4. Impedance spectra in Nyquist representation of CH/CPE electrode in 0.1 M KNO3 electrolyte: (a) at different polarization potentials and (b) at different pH values.
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Figure 5. Impedance spectra in the Nyquist diagrams in 0.1 M KNO3 in the presence of different concentrations of Pb2+ recorded on: (a) CH/CPE, (b) TiO2-CH/CPE, and (c) NiO-CH/CPE electrodes. (d) Equivalent electric circuit proposed to fit the impedance spectra.
Figure 5. Impedance spectra in the Nyquist diagrams in 0.1 M KNO3 in the presence of different concentrations of Pb2+ recorded on: (a) CH/CPE, (b) TiO2-CH/CPE, and (c) NiO-CH/CPE electrodes. (d) Equivalent electric circuit proposed to fit the impedance spectra.
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Figure 6. Calibration curves of the sensors: Rct0−Rct versus log ([Pb2+]/M).
Figure 6. Calibration curves of the sensors: Rct0−Rct versus log ([Pb2+]/M).
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Figure 7. Impedance spectra of Pb2+ solution in the absence and presence of Cd2+ in 0.1 M KNO3 electrolyte solution recorded on: (a) CH/CPE, (b) TiO2-CH/CPE, and (c) NiO-CH/CPE electrodes.
Figure 7. Impedance spectra of Pb2+ solution in the absence and presence of Cd2+ in 0.1 M KNO3 electrolyte solution recorded on: (a) CH/CPE, (b) TiO2-CH/CPE, and (c) NiO-CH/CPE electrodes.
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Figure 8. Optimized structures of the unit cell of chitosan (a), the Pb2+-chitosan complex (b), and the Cd2+-chitosan complex (c).
Figure 8. Optimized structures of the unit cell of chitosan (a), the Pb2+-chitosan complex (b), and the Cd2+-chitosan complex (c).
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Table 1. The values of the Rct in equivalent circuit fitted in the Nyquist plots of Figure 5 as a function of Pb2+ concentration.
Table 1. The values of the Rct in equivalent circuit fitted in the Nyquist plots of Figure 5 as a function of Pb2+ concentration.
[Pb2+]CH/CPETiO2-CH/CPENiO-CH/CPE
Rct (Ohm.cm2)Rct (Ohm.cm2)Rct (Ohm.cm2)
011,476703215,385
10−610,42248119744
10−5843546928585
10−4470346105423
Table 2. Comparison of various electrode materials for Pb2+ sensing.
Table 2. Comparison of various electrode materials for Pb2+ sensing.
Electrode MaterialAnalytical MethodLinear Range (M)LOD (M)Reference
Poly (dimethylsiloxane) microchipIndirect amperometry5.10−6 to10−31.3.10−6[85]
Poly (1,8-diaminonaphthalene) modified CPEDifferential pulse voltammetry2.10−7 to 10−51.4.10−7[86]
ZYMCPE on ITOCyclic voltammetry2.5.10−8 to 10−71.7.10−8[87]
Bismuth/glassy carbon compositeAnodic stripping voltammetry5.10−7 to 10−710−8[88]
Antimony film electrodeAnodic stripping voltammetry10−7 to 7.10−74.10−9[89]
CH/CPE, TiO2-CH/CPE, NiO-CH/CPEEIS10−6 to 10−4 3.10−7This work
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Boultif, W.; Dehchar, C.; Belhocine, Y.; Zouaoui, E.; Rahali, S.; Zouari, S.E.; Sbei, N.; Seydou, M. Chitosan and Metal Oxide Functionalized Chitosan as Efficient Sensors for Lead (II) Detection in Wastewater. Separations 2023, 10, 479. https://doi.org/10.3390/separations10090479

AMA Style

Boultif W, Dehchar C, Belhocine Y, Zouaoui E, Rahali S, Zouari SE, Sbei N, Seydou M. Chitosan and Metal Oxide Functionalized Chitosan as Efficient Sensors for Lead (II) Detection in Wastewater. Separations. 2023; 10(9):479. https://doi.org/10.3390/separations10090479

Chicago/Turabian Style

Boultif, Walid, Charif Dehchar, Youghourta Belhocine, Emna Zouaoui, Seyfeddine Rahali, Salah Eddine Zouari, Najoua Sbei, and Mahamadou Seydou. 2023. "Chitosan and Metal Oxide Functionalized Chitosan as Efficient Sensors for Lead (II) Detection in Wastewater" Separations 10, no. 9: 479. https://doi.org/10.3390/separations10090479

APA Style

Boultif, W., Dehchar, C., Belhocine, Y., Zouaoui, E., Rahali, S., Zouari, S. E., Sbei, N., & Seydou, M. (2023). Chitosan and Metal Oxide Functionalized Chitosan as Efficient Sensors for Lead (II) Detection in Wastewater. Separations, 10(9), 479. https://doi.org/10.3390/separations10090479

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