# Graphene oxide-infused hybrid nanocomposite for the targeted and precise simultaneous detection of lead and cadmium ions

Afef Dhaffouli, Younes Moussaoui, Pedro Salazar-Carballo, Michael Holzinger, Soledad Carinelli, Houcine Barhoumi

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Afef Dhaffouli, Younes Moussaoui, Pedro Salazar-Carballo, Michael Holzinger, Soledad Carinelli, et al.. Graphene oxide-infused hybrid nanocomposite for the targeted and precise simultaneous detection of lead and cadmium ions. Inorganic Chemistry Communications, 2025, 180, pp.114871. 10.1016/j.inoche.2025.114871. hal-05158661

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Graphene oxide-infused hybrid nanocomposite for the targeted and precise
simultaneous detection of lead and cadmium ions

Afef Dhaffouli<sup>a,b,∗</sup> , Younes Moussaoui<sup>b,c</sup> , Pedro A. Salazar-Carballo<sup>c</sup> , Michael Holzinger<sup>d</sup> ,
Soledad Carinelli<sup>c</sup> , Houcine Barhoumi<sup>a</sup>

<sup>a</sup> Laboratory of Interfaces and Advanced Materials, University of Monastir, Faculty of Sciences of Monastir 5000 Monastir, Tunisia

<sup>b</sup> Department of Chemistry, University of Gafsa, Faculty of Sciences of Gafsa 2100 Gafsa, Tunisia

<sup>c</sup> Laboratory of Sensors, Biosensors and Advanced Materials, Faculty of Health Sciences, University of La Laguna, Campus de Ofra s/n, 38071 La Laguna, Spain

<sup>d</sup> Department of Molecular Chemistry UMR CNRS 5250, Nanobio Building Grenoble-Alpes University, CS 40700 38058 Grenoble cedex 9, France

<sup>e</sup> University of Sfax, Faculty of Sciences of Sfax, Organic Chemistry Laboratory (LR17ES08), Sfax 3000, Tunisia

A B S T R A C T

In this study, a novel GO@ZnO@SiO₂ nanocomposite was synthesized and used to modify a glassy carbon electrode for potential electrochemical applications. Zinc oxide nanoparticles were synthetized and coated with a silica shell. Finally, ZnO@SiO₂ particles were combined with graphene oxide (GO) to form the GO@ZnO@SiO₂ nanocomposite. This nanocomposite was characterized using FE-SEM, TEM, EDS, FT-IR, and XRD techniques to evaluate its morphology, elemental composition, functional groups, and crystalline structure. Such techniques confirmed the successful synthesis of the nanocomposite and its suitability for electrode surface modification. Electrochemical test confirmed that the combination of the high surface area and conductivity of GO, the stability of SiO₂, and the electrocatalytic properties of ZnO enhanced the performance of the sensor for simultaneous detection of Pb(II) and Cd(II) ions in aqueous solutions. Differential pulse voltammetry (DPV) was used for sensor evaluation, and the key parameters were optimized. The sensor showed two distinct concentration ranges for each metal ion, with limits of detection of 7.5 × 10⁻⁹ M for Pb(II) and 1.25 × 10⁻⁸ M for Cd(II). The device also demonstrated high selectivity towards Pb(II) and Cd(II), with recovery rates between 81 % and 104 % in real water samples.

**1. Introduction**

Heavy metal contamination, particularly lead (Pb²⁺) and cadmium (Cd²⁺), has emerged as a critical global concern due to their high toxicity [1–3], long-term persistence, and tendency to bioaccumulate in living organisms [4]. Their widespread presence in aquatic systems is primarily attributed to industrial discharges, mining operations, battery production, and fossil fuel combustion. Once released into the environment, these ions can enter biological systems through water or food intake, leading to severe health disorders including nephrotoxicity, neurotoxicity, and endocrine disruption, even at trace concentrations [5–7]. Given their frequent co-occurrence in contaminated environments, it is crucial to develop analytical tools capable of simultaneous and selective detection of Pb²⁺ and Cd²⁺ [8–11]. Classical techniques such as atomic absorption spectroscopy [12], inductively coupled

plasma mass spectrometry [13], and atomic fluorescence spectrometry
[14], high-performance liquid chromatography [15], and X-ray fluo-
rescence [16] are well established for trace-level detection. However,
their costly instrumentation, time-consuming procedures, and the need
for specialized personnel limit their applicability for on-site monitoring
[17]. In contrast, electrochemical sensing platforms offer several
attractive features, including low cost, operational simplicity, rapid
response, and potential for miniaturization, making them ideal for
portable and real-time applications [18-20]. Among these, differential
pulse voltammetry (DPV) has gained increasing attention due to its
excellent sensitivity and signal resolution in detecting trace levels of
heavy metals [21-23]. However, the challenge lies in enhancing the
selectivity and sensitivity of the electrode interface to distinguish metal
ions in complex matrices such as natural waters [24,25]. To address this,
numerous studies have explored the functionalization of electrodes
using magnetic nanoparticles [26], surfactants [27-29], polymers [30-33], and carbon-based nanomaterials [34,35]. In particular, gra-
phene oxide (GO) has demonstrated remarkable potential due to its two-
dimensional structure, oxygen-containing functional groups, and large
electroactive surface area [36], which facilitate strong interactions with
metal ions and promote efficient electron transfer [37,38]. Modifying
GO with other nanostructures, such as metal oxides or silica, has been
shown to significantly enhance detection performance [39]. For
instance, zinc oxide (ZnO) nanoparticles are known for their high
adsorption capacity and affinity for divalent metal ions, while silica
nanoparticles (SiO₂) offer chemical stability, surface hydroxyl groups,
and improved dispersion of nanomaterials on the electrode surface [40].

Recent studies have reported various graphene oxide (GO)-based composites for the detection of heavy metals. For instance, Luyen et al., (2024) demonstrated that ZnO/ErGO composite was a promising material for Cd(II) and Pb(II) detection [41], primarily due to their enhanced active surface area and improved peak separation in voltammetric analyses. Furthermore, the choice of different materials such as GO, ZnO, and SiO₂ is driven not only by their advantageous electrochemical characteristics but also by their affordability and straightforward synthesis procedures [42-44], which support large-scale fabrication and practical deployment in on-site sensing platforms. Although notable progress has been made in the design of electrochemical sensors for heavy metal detection, many existing systems continue to face challenges, including inadequate sensitivity, limited effectiveness in real sample analysis, and weak synergistic interactions among the composite constituents.

In this work, we propose a novel hybrid nanocomposite electrode based on graphene oxide (GO) functionalized with zinc oxide (ZnO) and silica (SiO₂) nanoparticles, which are readily available and can be synthesized using cost-effective, scalable methods, for the simultaneous electrochemical detection of Pb²⁺ and Cd²⁺ in water. This three-component system is designed to harness the individual strengths of each component: (i) GO offers excellent electrical conductivity and a large number of active sites; (ii) ZnO contributes strong affinity toward heavy metal ions and enhances electrochemical reactivity; and (iii) SiO₂ nanoparticle dispersion and introduces surface hydroxyl groups that facilitate metal ion adsorption. To the best of our knowledge, this specific combination of GO@ZnO@SiO₂ in a single sensing platform, applied for the simultaneous detection of Pb²⁺ and Cd²⁺, represents a novel approach that has not yet been reported in the literature. Furthermore, the composite material was easily drop-cast onto a glassy carbon electrode (GCE), and the electrochemical parameters for differential pulse voltammetry (DPV) were thoroughly optimized. The sensor's performance was also validated with real water samples, including tests under complex matrix conditions involving humic substances and common surfactants, confirming its potential for practical for environmental monitoring applications.

2. Experimental

2.1. Chemicals

Chemicals utilized originated from Sigma-Aldrich: zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O), Graphene oxide (GO), ethanol (EtOH, 96 %), Al₂O₃, and tetraethyl orthosilicate (TEOS), potassium chloride (KCl), Sodium hydroxide (NaOH), copper(II) chloride (CuCl₂), Hydrochloric acid(HCl,37 %), sulfuric acid (H₂SO₄), ethylenediaminetetraacetic acid (EDTA), monosodium dihydrogen phosphate trihydrate (KH₂PO₄·3H₂O) and disodium hydrogen phosphate dodecahydrate (Na₂HPO₄·12H₂O), lead(II) nitrate (Pb(NO₃)₂), manganese chloride (MnCl₂), cobalt nitrate (Co(NO₃)₂), potassium hexacyanoferrate(III) (K₃[Fe(CN)₆]), cadmium(II) nitrate tetrahydrate (Cd(NO₃)₂·4H₂O), hydrazine hydrate (H₆N₂O), potassium hexacyanoferrate(II) trihydrate (K₄[Fe(CN)₆]·3H₂O).

For the electrochemical studies, a 0.1 M acetate buffer solution (pH

5.0) was prepared by mixing equimolar of acetic acid (CH₃COOH) and
sodium acetate (CH₃COONa). The pH of the buffer was adjusted as
needed using NaOH or HCl.

## 2.2. Synthesis of ZnO NPs

For the synthesis of zinc oxide (ZnO) nanoparticles, 2.0 g of zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O) was dissolved in 50 mL of ethanol under continuous stirring until fully dissolved. Separately, a 0.1 M sodium hydroxide (NaOH) solution was prepared by dissolving 0.4 g of NaOH in 100 mL of distilled water. Then, 2 mL of the NaOH(0.1 M) solution was added dropwise to the zinc acetate solution under continuous stirring to initiate the precipitation of zinc hydroxide (Zn(OH)₂). The mixture was stirred for 1 h at room temperature to ensure complete precipitation. Subsequently, the suspension was heated at 80 °C for 2 h to promote the transformation of Zn(OH)₂ to ZnO nanoparticles. To facilitate this conversion, 1 mL of hydrazine hydrate was added as a reducing agent, and the mixture was stirred continuously at room temperature for an additional 1 h. After cooling to room temperature, the ZnO nanoparticles were separated by centrifugation at 10,000 rpm for 10 min. The precipitate was washed at least twice with a 1:1 mixture of distilled water and ethanol to remove residual impurities. Finally, the product was dried in an oven at 80 °C for 24 h, yielding a yielding a fine white powder of ZnO nanoparticles.

2.3. Synthesis of Go@ZnO@SiO₂ nanocomposite

To guarantee uniform dispersion, 0.2 g of the synthesized ZnO nanoparticles were dispersed in 50 mL of a 1:1 mixture of ethanol and distilled water using an ultrasonic bath for one hour. After that, tetraethyl orthosilicate (TEOS, 3 mL) and ammonia solution (1 M, 1.6 mL) were added sequentially under vigorous stirred. The resulting ZnO@-SiO₂ composite (denoted as A) was obtained by thoroughly washing the mixture with ethanol and distilled water, followed by drying in an oven at 60 °C for 12 h. Graphene oxide (GO) was synthesized from graphite powder using a modified Hummers method [45]. For the preparation of the hybrid material, 1 g of GO was weighed and dispersed in distilled water, followed by ultrasonic treatment to ensure uniform dispersion. This GO suspension was then added to a dispersion of 0.3 g of the ZnO@SiO₂ composite (A) under continuous stirring, resulting in a homogeneous mixture. After the reaction, the mixture was centrifuged, and residual chemicals were removed by repeatedly washing the solid with ethanol and distilled water. Finally, the Go@ZnO@SiO₂ nanocomposite was obtained by vacuum-drying the product at 60 °C for 24 h.

## 2.4. Fabrication of Go@ZnO@SiO₂/GCE modified electrode

Before to the electrode modification, the surface of the glassy carbon electrode (GCE) was carefully polished using wet 0.05 µm Al₂O₃ powder on a suede cloth. The electrode was then cleaned ultrasonically in ethanol and subsequently in distilled water, each for 5 min. To prepare the modifying suspension, 5 mg of the sample was dispersed in 5 mL of ethanol and sonicated to obtain a uniform suspension. Then, 5.0 µL of the resulting 5 mg/mL suspension was drop-cast onto the GCE surface. The modified electrode was allowed to dry at room temperature in ambient air for 3 h before being used for electrochemical measurements.

## 2.5. Characterization of Go@ZnO@SiO₂ nanocomposite

The surface morphology of the GO@ZnO@SiO₂ nanocomposite was characterized using Field Emission Scanning Electron Microscopy (FE-SEM, JEOL 6701F, Japan) and Transmission Electron Microscopy (TEM, JSM2100, JEOL, Japan). To investigate its structural features and identify functional groups, Energy-Dispersive X-ray Spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FT-IR, Spectrum 100, PerkinElmer) were employed. Furthermore, the crystalline structure of
the composite was analyzed by X-ray Diffraction (XRD) using a Rigaku diffractometer equipped with Cu Kα radiation (λ= 1.5406 Å).

The electrochemical behavior of the composite was studied using an Autolab PG (AUT 83965) system. A conventional three-electrode configuration was employed, comprising a platinum (Pt) wire (0.5 mm diameter) as the counter electrode, a glassy carbon electrode (GCE, 3 mm diameter) as the working electrode, and a saturated Ag/AgCl reference electrode (0.5 mm diameter) with 3 M KCl. Electrochemical characterization was conducted out using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) in a solution of ferri-cyanide/ferrocyanide containing 0.1 M KCl. For the quantitative analysis of cadmium (Cd) and lead (Pb), Differential Pulse Voltammetry (DPV) was carried out over a potential range of - 1.0 V to - 0.4 V.

# 3. Results and discussion

## 3.1. Characterization

### 3.1.1. Structure and morphology of Go@ZnO@SiO₂

The structural features of GO, ZnO, and the GO@ZnO@SiO₂ nanocomposite were investigated using X-ray diffraction (XRD). The diffractogram of graphene oxide (GO), see Fig. 2a, exhibits a sharp and intense peak at 2θ ≈ 26°, which corresponds to the (002) crystallographic plane. This prominent reflection indicates a high degree of stacking among GO layers, suggesting limited exfoliation and strong interlayer interactions. Additional weak reflections at 2θ ≈ 43.42° and 44.47°, assigned to the (100) and (101) planes, reflect some degree of in-plane ordering within the sp²-hybridized carbon domains. On the other hand, ZnO XRD pattern displays well-defined peaks at 2θ ≈ 32.09°, 34.81°, 36.67°, and 47.94°, corresponding to the (100), (002), (101) and (102) planes, of the hexagonal wurtzite structure, consistent with the JCPDS card No. 36-1451 [46]. The sharpness and high intensity of these reflections confirm the successful synthesis of highly crystalline ZnO, with no detectable secondary phases or structural defects. The composite GO@ZnO@SiO₂ reveals a superposition of the characteristic features of each constituent. Reflections at 2θ ≈ 31.72°, 34.38°, 36.24°, 44.53°, and 47.38° confirm the preservation of the wurtzite ZnO phase after incorporation into the hybrid material. A broad and diffuse band

around 2θ ≈ 22.61° is observed, which is typically associated with amorphous silica, indicating the successful deposition of a non-crystalline SiO₂ phase (inset, Fig. 2a). Notably, the intense peak at 2θ ≈ 26.21°, attributed to the (002) plane of GO, remains clearly visible in the composite, confirming the structural integrity and retention of phenic stacking within the final hybrid system [47].

The reduction in intensity and broadening of this peak can be attributed to the partial exfoliation of GO sheets or interactions with ZnO nanoparticles and silica, which disrupt the regular stacking of GO layers. Importantly, no sharp peaks corresponding to SiO₂ are detected in the composite spectrum, indicating that the silica is amorphous, consistent with sol-gel derived SiO₂ materials. The amorphous silica likely enhances the dispersion of ZnO and GO, while also providing functional surfaces rich in silanol groups that can promote interfacial bonding. Overall, the XRD analysis confirms the successful synthesis of the GO@ZnO@SiO₂ hybrid material, combining the crystalline ZnO structure, the layered features of GO, and the amorphous nature of silica which together contribute to the composite's enhanced properties.

### 3.1.2. Morphological characterization of graphene oxide (GO) and GO@ZnO@SiO₂ nanocomposite by SEM and TEM Analyse

The SEM and TEM images provide clear evidence of the successful synthesis and morphological evolution from graphene oxide (GO) to the GO@ZnO@SiO₂ nanocomposite. The SEM image of pristine GO (Fig. 1a) reveals thin, crumpled, sheet-like structures with a layered and wrinkled appearance, characteristic of exfoliated GO. This morphology indicates a high surface area, which is favorable for subsequent functionalization or nanoparticle decoration. Upon incorporation of ZnO and SiO₂ (Fig. 1b and c), the SEM images show bright, granular particles uniformly distributed across the GO sheets. These particles are attributed to ZnO and SiO₂, indicating their successfully anchored onto the GO surface. The distinct contrast and aggregated structures confirm the formation of a hybrid nanocomposite, with ZnO likely exhibiting a more crystalline nature and SiO₂ a more spherical or amorphous morphology. Complementary insights from the TEM analysis further validate the formation of the composite. The TEM image of GO alone (Fig. 1d) shows transparent, flexible sheets with irregular edges, reflecting the ultrathin, and two-dimensional nature of GO. After modification (Fig. 1e and f),

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** SEM images of (a) pristine graphene oxide (GO), (b, c) GO@ZnO@SiO₂; TEM images of (d) GO sheets, (e, f) GO@ZnO@SiO₂ nanocomposite.</figcaption></figure>
spherical dark nanoparticles are clearly visible across the GO matrix. The higher electron density of these particles, particularly ZnO, accounts for their strong contrast. The smaller, well-dispersed spherical particles are consistent with SiO₂, indicating good distribution and interaction with the GO sheets. The intimate contact between the nanoparticles and the GO matrix demonstrates the homogeneous integration of all components. In summary, the SEM and TEM results collectively confirm the successful fabrication of the GO@ZnO@SiO₂ nanocomposite.

### 3.1.3. EDS analysis

The analysis presented in Fig. S1 provides insight into the elemental composition of two samples: pure graphene oxide (GO) and the GO@ZnO@SiO₂ composite. In the spectrum of GO (Fig. S1a), strong peaks corresponding to carbon and oxygen confirm the typical structure of GO, which is rich in carbon and functionalized with oxygen-containing groups. In contrast, the EDS spectrum of the composite material (Fig. S1b) shows additional peaks for zinc and silicon, indicating the successful incorporation of ZnO and SiO₂ nanoparticles into the GO matrix. The quantitative data in Table S1 support these observations, showing a high carbon content (82.05 %), along with notable amounts of oxygen (11.78 %), silicon (3.33 %), and zinc (2.83 %). These values confirm that GO remains the primary component, while ZnO and SiO₂ are present in smaller but significant quantities. The relatively low error

margins, particularly for carbon and oxygen, reflect the reliability of the measurements. Overall, the EDS results clearly demonstrate the formation of a composite material where ZnO and SiO₂ nanoparticles are well-integrated into the GO structure.

### 3.1.4. FTIR characterization

The FTIR spectrum provides clear evidence for the successful synthesis and integration of the GO@ZnO@SiO₂ nanocomposite (see Fig. 2b). In the reference spectrum of ZnO a prominent band at approximately 397 cm⁻¹ is assigned to the Zn-O stretching mode, confirming the presence of ZnO nanoparticles [48]. This peak remains evident in the ZnO@SiO₂ spectrum, where additional bands emerge in the 940-1035 cm⁻¹ region due to silica network formation specifically, the Si-O-Si asymmetric stretching at 1060 cm⁻¹, and Si-O-Zn at 912 cm⁻¹, indicating effective bonding between silica and ZnO [49]. Upon incorporation of GO into the system, forming the GO@ZnO@SiO₂ hybrid, several key changes are observed. Notably, the Zn-O and Si-O related bands, particularly the one at 397 cm⁻¹, are significantly diminished or masked. This attenuation suggests that the ZnO@SiO₂ particles are well-encapsulated or embedded within the GO matrix, limiting their direct vibrational expression due to the surrounding carbon-based network. In addition, new absorption bands corresponding to GO functional groups are clearly visible, including aliphatic -CH₂

<figure><img src="image_3.png" /><figcaption>**Fig. 2.** XRD Patterns of GO, ZnO, and GO@ZnO@SiO₂ nanocomposite (a), FTIR Spectra of ZnO, SiO₂, ZnO@SiO₂, and GO@ZnO@SiO₂ Nanocomposites(b), Electrochemical characterization of bare GCE, ZnO@SiO₂/GCE, and GO@ZnO@SiO₂/GCE: (c) Cyclic voltammograms; (d) Nyquist plots obtained from EIS measurements with corresponding equivalent circuit model (inset).</figcaption></figure>
stretches at 2969 and 2870 cm⁻¹, carbonyl (C=O) stretching at 1390 cm⁻¹, and C-O/C-O-C vibrations in the 1035-1060 cm⁻¹ range [50,51]. These features confirm the presence of oxygen-containing groups from GO and their interaction with the ZnO@SiO₂ surface. The overall spectrum indicates that the ZnO@SiO₂ components are not merely mixed but chemically integrated into the GO framework, supporting the formation of a structurally unified and well-dispersed hybrid nanocomposite.

### 3.1.5. Electrochemical characteristics of Go@ZnO@SiO₂NPs

The electrochemical behavior of bare GCE, ZnO@SiO₂-modified GCE, and GO@ZnO@SiO₂-modified GCE was assessed using electrochemical impedance spectroscopy (EIS) in a solution containing 0.1 M KCl and 5 mM [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻, as well as cyclic voltammetry (CV). As shown in the CV results, modification of the GCE with ZnO@SiO₂ leads to a marked decrease in the redox peak current and a significant increase in the peak-to-peak separation (ΔEₚ = 161 mV) (Fig. 2c), indicating sluggish electron transfer kinetics due to the poor conductivity of the ZnO@SiO₂ material. However, when the ZnO@SiO₂ composite is incorporated into GO, the resulting GO@ZnO@SiO₂/GCE exhibits a considerable enhancement in redox current and a reduced ΔEₚ, suggesting improved charge transfer properties. This improvement is attributed to the excellent conductivity of graphene oxide, which facilitates electron mobility and compensates for the insulating nature of the oxide matrix.

The EIS data support these findings and provide further insight into interfacial charge transfer behavior (Fig. 2d). The Nyquist plots were analyzed using an equivalent electrical circuit that includes double layer capacitance (Cdl), charge transfer resistance (Rct), solution resistance (Rs), and Warburg impedance (Zw), effectively modeling ion diffusion. In this model, Rs represents the resistance of the electrolyte, Rct indicates the difficulty of electron transfer at the electrode interface, Cdl reflects the capacitive behavior of the electrode/electrolyte interface, and Zw characterizes the diffusion-controlled processes. The extracted Rct values show a clear trend: ZnO@SiO₂/GCE exhibits the highest resistance (1804.05 Ω), followed by GO@ZnO@SiO₂/GCE (543.63 Ω), while the bare GCE has the lowest (246.06 Ω). This confirms that ZnO@SiO₂ impedes charge transfer due to its low conductivity, whereas the incorporation of GO significantly lowers Rct by improving the electrical pathways at the interface. Therefore, the circuit analysis further validates that the GO@ZnO@SiO₂ composite enhances electron transfer kinetics and provides a more efficient electrochemical interface, making it a promising material for sensor applications.

## 3.2. Electrochemical and analytical optimizations

Before proceeding to the optimization of the main experimental parameters, we evaluated the stability of our composite material in the electrolyte solution (acetate buffer) to ensure that no secondary effects would impact on its crystallinity or surface functional groups (see Fig. S2). To simulate post-use conditions and assess structural stability, 0.2 g of the catalyst was dispersed in 0.1 M acetate buffer (pH 5) and stirred for 1 h. The material was then recovered by centrifugation, dried overnight at 60 °C, and subsequently analyzed by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). The XRD patterns of the treated catalyst showed slightly broader peaks with reduced intensity compared to the fresh sample, indicating a minor loss of crystallinity while preserving the main phase structure. The FT-IR spectra exhibited similar characteristic bands before and after treatment, with slight shifts in position and intensity, suggesting limited interaction with the buffer solution and no significant alteration of the surface functional groups.

### 3.2.1. Experimental parameters optimization for Pb²⁺ and Cd²⁺ detection using GO@ZnO@SiO₂

To ensure optimal electrochemical performance of the GO@ZnO@-

SiO₂-modified electrode for the simultaneous detection of Pb²⁺ and Cd²⁺, key experimental parameters were systematically optimized using differential pulse voltammetry (DPV). All optimization studies were conducted using fixed concentrations of 1 × 10⁻⁵ M for each target ion in acetate buffer.

As an initial step, the influence of various supporting electrolytes on the electrochemical response of Pb²⁺ and Cd²⁺ ions were systematically examined (Fig. S3). The results clearly indicate that both the composition and pH of the electrolyte significantly impact the peak current intensity and overall sensitivity of detection at the GO@ZnO@SiO₂-modified electrode. Among the tested media 0.1 M acetate buffer (pH 5.0), 0.1 M PBS (pH 7.0), 0.1 M H₂SO₄ (pH 1.0), and 0.1 M NaOH (pH 13.0), the acetate buffer at pH 5.0 yielded the highest peak currents and the most well-defined signals for both metal ions. This enhanced performance can be attributed to the mildly acidic environment of the acetate buffer, which helps maintain Pb²⁺ and Cd²⁺ in their soluble ionic forms and promotes favorable interactions with the active sites on the electrode surface [52]. In contrast, the signal for Pb²⁺ significantly diminished in PBS at pH 7.0, likely due to partial hydrolysis and precipitation of Pb²⁺ as Pb(OH)₂ under near-neutral conditions, reducing its availability for electrochemical detection [53]. Similarly, both strongly acidic (H₂SO₄, pH 1.0) and strongly basic (NaOH, pH 13.0) media resulted in lower current responses. This decrease may stem from excessive surface protonation in acidic media or hydroxide complexation and precipitation in alkaline environments, both of which hinder effective metal ion adsorption [54]. These findings confirm that 0.1 M acetate buffer at pH 5.0 offers the most favorable conditions for achieving high sensitivity and signal resolution in the simultaneous electrochemical detection of Pb²⁺ and Cd²⁺.

Additionally, the volume of the nanocomposite suspension (5 mg/ml) drop-cast onto the glassy carbon electrode (GCE) surface was evaluated. As shown in Fig. 3a, increasing the deposited volume from 2 to 7 µL led to a steady enhancement in peak current for both Pb²⁺ and Cd²⁺, with maximum responses of approximately 33 µA and 17 µA, respectively, observed at 7 µL. This improvement is attributed to the greater active surface area and higher loading of the electroactive nanocomposite. However, further increases in volume led to a slight decline in current response, likely due to the formation of a thicker film that hindered electron transfer and ion diffusion at the electrode - electrolyte interface [55]. Drying time significantly affected the stability and performance of the modified film. As depicted in Fig. 3b, the optimal drying time was found to be 2 h, yielding peak currents of approximately 31 µA for Pb²⁺ and 17 µA for Cd²⁺. Prolonged drying (up to 14 h) slightly reduced the signal, possibly due to microstructural changes such as shrinkage or densification of the film, which can lower its conductivity and reduce electrochemical accessibility.

The pH of the supporting electrolyte also plays a crucial role in modulating both the surface charge of the electrode and the chemical speciation of metal ions in solution. As shown in Fig. 3c, the peak currents for both Pb²⁺ and Cd²⁺ increased as the pH rose from 4.0 to 5.0, reaching maximum values (~30 µA for Pb²⁺ and ~ 16 µA for Cd²⁺) at pH 5.0. This enhancement is attributed to the reduced competition from proton for active sites and the improved adsorption of metal ions at near-neutral pH [56]. Above pH 5.0, a decrease in signal was observed, likely due to the formation of poorly soluble hydroxide species (Pb(OH)₂ or Cd(OH)₂), which limits the concentration of free metal ions available for electrochemical reduction [57-59]. At lower pH values, excessive protonation of the electrode surface and competition from H⁺ ions can hinder metal ion adsorption, thereby weakening the electrochemical signal [60].

In this study, the accumulation time was varied from 1 to 10 min to evaluate its effect on the simultaneous detection of Pb²⁺ and Cd²⁺ ions. As shown in Fig. 3d, the peak currents increased significantly with longer accumulation times, reaching maximum values of approximately 31 µA for Pb²⁺ and 20 µA for Cd²⁺ at 5 min. Beyond this point, the current response stabilized, indicating saturation of the active
<figure><img src="image_4.png" /><figcaption>Fig. 3. Effect of different experimental conditions on the electrode's response: (a) Effect of the quantity of matrix applied to the electrode, (b) Effect of drying time, (c) Influence of pH on the electrode response, and (d) Impact of accumulation time. The measurements were performed in an acetate buffer (0.1 M) containing $10^{-5}$ M of $Cd^{2+}$ and $Pb^{2+}$.</figcaption></figure>

adsorption sites on the surface of the GO@ZnO@SiO₂-modified electrode surface. This saturation limits further ion accumulation, suggesting that 5 min is the optimal accumulation time to achieve high sensitivity and effective preconcentration of metal ions with the developed sensor.

### 3.2.2. Selective detection of $Cd^{2+}$

A modified electrode incorporating GO@ZnO@SiO₂ was employed for the determination of cadmium ions ($Cd^{2+}$) in a 0.1 M acetate buffer solution at pH 5. The detection conditions were carefully optimized: 7 µL of the casting solution was deposited on the electrode surface, followed by 3 h drying period. For electrochemical analysis accumulation time was fixed to 5 min. The voltammetric analysis revealed a prominent reduction peak around - 0.78 V, with peak current intensities increasing consistently as $Cd^{2+}$ concentration increased, confirming the system's sensitivity. Notably, the calibration curve exhibited two distinct linear regions: from $1 \times 10^{-8}$ M to $7.5 \times 10^{-8}$ M ($R^2$ = 0.9814), likely associated with high-affinity adsorption on active sites, and from $7.5 \times 10^{-8}$ M to $2 \times 10^{-7}$ M ($R^2$ = 0.9954), which may correspond to saturation of those sites and the involvement of lower-affinity or secondary adsorption processes (See Fig. S4). This dual linearity is likely influenced by the electrocatalytic nature of the nanomaterial. At lower concentrations, the large active surface area and high conductivity of the GO@ZnO@SiO₂ composite enhance electron transfer, resulting in a sharp and linear

response. As the concentration increases, surface saturation or changes in the interaction between the analyte and the active sites may occur, slightly modifying the sensor's response and giving rise to a second linear range. The system achieved a detection limit as low as $1.5 \times 10^{-8}$ M, underscoring its potential for sensitive, trace-level detection of cadmium in various analytical applications.

### 3.2.3. Selective detection of $Pb^{2+}$

The electrochemical detection of $Pb^{2+}$ ions using a GO@ZnO@SiO₂-modified electrode is presented in Fig. S5, with measurements performed by differential pulse voltammetry (DPV). The voltammograms show a clear and progressive increase in peak current with rising $Pb^{2+}$ concentrations, indicating efficient interaction between the metal ions and the sensor surface. Two distinct linear response intervals were identified: from $5 \times 10^{-9}$ M to $1.75 \times 10^{-8}$ M ($R^2$ = 0.9879), and from $1.75 \times 10^{-8}$ M to $2 \times 10^{-7}$ M ($R^2$ = 0.9941). This biphasic response likely reflects a transition from rapid adsorption at high-affinity sites to a slower accumulation governed by site heterogeneity or saturation effects at higher concentrations. The calculated limit of detection (LOD), $7.5 \times 10^{-9}$ M, highlights the sensor's ability to detect trace levels of lead with high sensitivity and precision. It is worth noting that, in earlier investigations by Dhaffouli et al. [40], the ZnO@SiO₂ composite alone exhibited selective sensitivity toward $Cd^{2+}$ ions, with limited effectiveness in detecting $Pb^{2+}$. However, in the present study, the incorporation
of ZnO@SiO₂ into graphene oxide (GO) significantly enhanced the sensor's performance for Pb²⁺ detection. GO provides a large surface area enriched with oxygen-containing functional groups, which promotes efficient adsorption and facilitate electron transfer [61]. Additionally, its unique layered structure creates microporous networks and active cavities that serve as favorable sites for Pb²⁺ accumulation and redox reactions. Furthermore, ZnO contributes as a semiconducting material that enhances charge mobility, while the silica matrix offers structural stability and ensures a homogeneous dispersion of the active components. The synergistic integration of GO, ZnO, and SiO₂ thus results in a highly responsive and selective platform for lead detection. In conclusion, the GO@ZnO@SiO₂ nanocomposite demonstrates excellent electrocatalytic properties, making it a promising sensing interface for detection of Pb²⁺ ions in environmental samples, even at ultra-trace levels.

### 3.2.4. Simultaneous detection of Cd²⁺ and Pb²⁺

Fig. 4 illustrates the simultaneous electrochemical detection of Pb²⁺ and Cd²⁺ using a GO@ZnO@SiO₂ nanocomposite-modified electrode in an acetate buffer solution (0.1 M, pH 5). Two well-defined reduction peaks are observed at approximately -0.78 V for Cd²⁺ and -0.5 V for Pb²⁺, confirming the sensor's high selectivity and capacity for distinguishing between these two metal ion. The current responses increase proportionality with rising analyte concentrations, indicating efficient electrochemical interaction and signal responsiveness. The calibration curves for both ions exhibit dual linear ranges. For Cd²⁺, the first range

extends from 5 × 10⁻⁹ to 1.75 × 10⁻⁸ M (R² = 0.9844), followed by a second linear range from 1.75 × 10⁻⁸ to 1.5 × 10⁻⁷ M (R² = 0.9970). Similarly, Pb²⁺ displays a first linear interval from 5 × 10⁻⁹ to 2 × 10⁻⁸ M (R² = 0.9774), and a second from 2 × 10⁻⁸ to 1.5 × 10⁻⁷ M (R² = 0.9931). These segmented linear responses likely reflect variations in adsorption dynamics, such as a transition from high-affinity active sites at low concentrations to saturation effects or lower-affinity interactions at higher concentrations. The limits of detection (LODs) were determined to be 1.25 × 10⁻⁸ M for Cd²⁺ and 7.5 × 10⁻⁹ M for Pb²⁺ demonstrating the system's high sensitivity for trace-level detection. To highlight the novelty of our sensor design and assess the contribution of the multi-component nanocomposite, we compared it with previously reported materials of simpler composition. For example, Nguyen Dinh Luyen et al. (2024) developed a ZnO/ErGO-modified electrode for simultaneous detection of Cd²⁺ and Pb²⁺, achieving limits of detection (LODs) of 1.5 × 10⁻⁸ M and 2.17 × 10⁻⁹ M, respectively [41]. While their system combined only ZnO and GO, our approach incorporates silica (SiO₂) as a third component, which significantly enhances material dispersion and introduces abundant surface hydroxyl groups that improve metal ion adsorption. As summarized in Table 1 [62–74], these results demonstrate the synergistic effect of combining GO, ZnO, and SiO₂. Graphene oxide provides excellent electrical conductivity and a high density of active sites; ZnO contributes catalytic activity and selective affinity toward metal ions; and SiO₂ offers a large surface area with functional groups that facilitate adsorption. Together, these features create an advanced sensing platform exhibiting superior

<figure><img src="image_5.png" /><figcaption>Fig. 4. Raw DPV of simultaneous detection of Cd²⁺ and Pb²⁺ Using a GO@ZnO@SiO₂ Nanocomposite Modified Electrode in solution containing ABS (0.1 M, pH5). The measurements were performed in an acetate buffer (0.1 M) at pH5.</figcaption></figure>
<table><caption>**Table 1**
Comparison of GO@ZnO@SiO₂-modified electrode with other reported sensors for simultaneous Cd²⁺ and Pb²⁺ detection.</caption><thead><tr><th rowspan="2">Electrode material</th><th rowspan="2">Technique used</th><th rowspan="2">Solvent</th><th colspan="2">Limit of detection (M)</th><th rowspan="2">pH of analyst</th><th rowspan="2">Reference</th></tr><tr><th>Cd²⁺</th><th>Pb²⁺</th></tr></thead><tbody><tr><td>GCE-MWCNT/poly-PCV/Bi</td><td>DPASV</td><td>Distilled water</td><td>1.78 × 10<sup>-9</sup></td><td>1.9 × 10<sup>-9</sup></td><td>5</td><td>[62]</td></tr><tr><td>GCE/ZSM-5/Pt</td><td>DPV</td><td>Distilled water</td><td>-</td><td>1.1 × 10<sup>-8</sup></td><td>5</td><td>[63]</td></tr><tr><td>Ce-Zr/GCE</td><td>SWASV</td><td>Distilled water</td><td>-</td><td>5.4 × 10<sup>-4</sup></td><td>5</td><td>[64]</td></tr><tr><td>RGO-GNPs</td><td>SWASV</td><td>Distilled water</td><td>7.1 × 10<sup>-10</sup></td><td>5.8 × 10<sup>-10</sup></td><td>5</td><td>[65]</td></tr><tr><td>CPE-ACC</td><td>SWV</td><td>Tap water</td><td>4.6 × 10<sup>-7</sup></td><td>8.4 × 10<sup>-8</sup></td><td>7</td><td>[66]</td></tr><tr><td>Fe<sub>3</sub>O<sub>4</sub>/MWCNTs/LSG/CS/GCE</td><td>SWASV</td><td>Distilled water</td><td>8.9 × 10<sup>-10</sup></td><td>3.4 × 10<sup>-10</sup></td><td>5</td><td>[67]</td></tr><tr><td>ZnFe<sub>2</sub>O<sub>4</sub>GCE</td><td>DPASV</td><td>Distilled water</td><td>2.2 × 10<sup>-8</sup></td><td>5.4 × 10<sup>-9</sup></td><td>5</td><td>[68]</td></tr><tr><td>ZnO@SiO<sub>2</sub></td><td>DPV</td><td>Distilled water</td><td>4.4 × 10<sup>-11</sup></td><td>-</td><td>5</td><td>[40]</td></tr><tr><td>ZnO/ErGO-GCE</td><td>DPASV</td><td>Distilled water</td><td>1.50 × 10<sup>-8</sup></td><td>2.17 × 10<sup>-9</sup></td><td>5.5</td><td>[41]</td></tr><tr><td>rGO/Au-Bi-GCE</td><td>DPASV</td><td>Distilled water</td><td>1.78 × 10<sup>-10</sup></td><td>2.41 × 10<sup>-10</sup></td><td>4.5</td><td>[69]</td></tr><tr><td>Bi/Graphene-PGE</td><td>SWASV</td><td>Distilled water</td><td>1.07 × 10<sup>-9</sup></td><td>1.40 × 10<sup>-9</sup></td><td>4.5</td><td>[70]</td></tr><tr><td>GSH/AuNPs/NH<sub>2</sub>-rGO-GCE</td><td>DPASV</td><td>Distilled water</td><td>8.01 × 10<sup>-10</sup></td><td>1.83 × 10<sup>-9</sup></td><td>4.5</td><td>[71]</td></tr><tr><td>Fe<sub>3</sub>O<sub>4</sub>@G2-PAD/MCPE</td><td>SWASV</td><td>Deionized water</td><td>1.87 × 10<sup>-9</sup></td><td>8.21 × 10<sup>-10</sup></td><td>5.5</td><td>[72]</td></tr><tr><td>GO-Fe<sub>3</sub>O<sub>4</sub>-PAMAM/GCE</td><td>SWASV</td><td>Ultra-pure water</td><td>6.23 × 10<sup>-10</sup></td><td>6.27 × 10<sup>-10</sup></td><td>4.5</td><td>[73]</td></tr><tr><td>GSH@Fe<sub>3</sub>O<sub>4</sub>/MGCE</td><td>SWASV</td><td>Deionized water</td><td>1.53 × 10<sup>-9</sup></td><td>8.78 × 10<sup>-10</sup></td><td>4.5</td><td>[74]</td></tr><tr><td>GO@ZnO@SiO<sub>2</sub></td><td>DPV</td><td>Distilled water</td><td>1.25 × 10<sup>-8</sup></td><td>7.5 × 10<sup>-9</sup></td><td>5</td><td>This Work</td></tr></tbody></table>

* **DPASV**: Differential pulse anodic stripping voltammetry; **DPV**: Differential pulse voltammetry; **SWASV**: Square wave anodic stripping voltammetry; **GCE**: Glassy Carbon Electrode; **MWCNT**: Multi-Walled Carbon Nanotubes; **poly-PCV**: Poly(1,2-dichloroethene-co-vinyl chloride); **Bi**: Bismuth; **ZSM-5**: Zeolite Socony Mobil-5; **Pt**: Platinum; **Ce-Zr**: Cerium-Zirconium; **RGO**: Reduced Graphene Oxide; **GNPs**: Gold Nanoparticles; **CPE**: Carbon Paste Electrode; **ACC**: Activated Carbon Composite; **LSG**: Layered Sodium Graphene; **CS**: Cysteine; **PAD**: polyamidoamine dendrimer; **PAMAM**: poly(amidoamine); **GO**: Graphene Oxide; **MGCE**: magnetic glassy carbon electrode; **GSH**: glutathione.

performance for the simultaneous detection of heavy metal ions in complex matrices.

The simultaneous detection of Pb²⁺ and Cd²⁺ ions using a GO@ZnO@SiO₂-modified GCE is governed by a synergistic mechanism that integrates surface adsorption and enhanced electron transfer processes (Fig. 5). The oxygen-containing groups on GO (e.g., -OH and -COOH) facilitate electrostatic attraction and coordination with Pb²⁺ and Cd²⁺ ions, meanwhile ZnO nanoparticles improve the electron transfer kinetics at the electrode interface, thereby amplifying the electrochemical signal. Additionally, the surface silanol groups (Si-OH) on SiO₂ serve as active binding sites, promoting further accumulation of metal ions through chemical interactions. During differential pulse voltammetry (DPV), the pre-concentrated metal ions are electrochemically reduced to their metallic states (Pb²⁺ and Cd²⁺), generating well-defined current peaks at characteristic reduction potentials.

## 4. Selectivity

The simultaneous detection of Pb²⁺ and Cd²⁺ was evaluated in the presence of common potentially interfering metal ions, including Co²⁺, Cu²⁺, Hg²⁺, Zn²⁺, and Mn²⁺, each introduced at a concentration ten times higher (1 × 10⁻⁵ M) than that of the target ions (2 × 10⁻⁷ M), as shown in Fig. 6. The sensor exhibited distinct and stable current responses for both Pb²⁺ and Cd²⁺, with only minor decreases in signal less than 1.5 µA in all cases (see Table S2). Specifically, the current response for Pb²⁺ ranged from 20.72 to 22.77 µA, while Cd²⁺ displayed values between 12.85 and 13.51 µA. These small variations indicate that the sensor maintains high selectivity and can simultaneously detect both target ions even in the presence of a significant excess of potentially interfering species. This selectivity is likely attributed to preferential binding or stronger electrostatic interactions between the sensor's active sites and the target metal ions. Overall, these results demonstrate that the proposed sensor is highly selective and suitable for trace-level

<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Proposed Interaction and Detection Mechanism of Pb(II)and Cd(II) on GO@ZnO@SiO₂-Modified Electrode.</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 6.** Effect of 1 × 10⁻⁵ M interfering ions on the concurrent detection of Pb²⁺ and Cd²⁺ using the GO@ZnO@SiO₂/GCE sensor. Measurements were performed after 5 min of accumulation in HAc-NaAc buffer (pH 5).</figcaption></figure>
detection of Pb²⁺ and Cd²⁺ in complex aqueous environments where multiple metal species coexisting.

**5. Stability, reusability, and reproducibility of the sensor**

To ensure the practical applicability of the developed GO@ZnO@-SiO₂-modified glassy carbon electrode (GCE), key performance parameters namely, storage stability, electrode reusability, and reproducibility were systematically evaluated and are presented in Fig. 7.

Fig. 7a illustrates the long-term stability of the GO@ZnO@SiO₂-modified glassy carbon electrode (GCE) for the simultaneous electrochemical detection of Pb²⁺ and Cd²⁺ ions at a concentration of 1 × 10⁻⁵ M over a period of 15 days. The electrode's performance was performed at regular intervals (days 1, 3, 5, 7, 9, and 15) to examine its response consistency after storage. For each measurement, the stored electrode was rinsed with distilled water and then used in a differential pulse voltammetry (DPV) test in a solution containing both metal ions. A gradual reduction in signal intensity was noted over time, suggesting a slight decline in surface activity, likely due to partial passivation or material aging. Despite this minor variation, the electrode exhibited strong reliability, with relative standard deviation (RSD) values of 4.79 % for Pb²⁺ and 3.50 % for Cd²⁺. The corresponding standard deviations (SD) were 4.01 µA and 2.92 µA, respectively, confirming good reproducibility and stable electrochemical behavior throughout the testing period.

Fig. 7b illustrates the intra-electrode reproducibility (repeatability) of the sensor. A single modified electrode was used for five consecutive measurements under identical conditions (see Fig. S6a). Between each run, the electrode was regenerated using 2 M EDTA to desorb residual metal ions, ensuring consistent surface activity. The low RSDs obtained (2.18 % for Pb²⁺ and 3.52 % for Cd²⁺) reflect excellent signal stability and effective regeneration, confirming the sensor's suitability for repeated use. To verify inter-electrode reproducibility, five independently prepared modified electrodes were tested under the same experimental conditions (Fig. 7c, Fig. S6b). The close agreement in current responses, with RSDs of 2.52 % for Pb²⁺ and 3.51 % for Cd²⁺, highlights the uniformity of the fabrication process and the reliability of the sensor design. Collectively, these results demonstrate that the sensor not only exhibits satisfactory long-term stability and regeneration capability but also ensures high reproducibility both within the same electrode and across different electrodes thereby fulfilling essential performance criteria for practical electrochemical sensing applications.

**6. Real sample analysis and recovery evaluation**

To evaluate the GO@ZnO@SiO₂/GCE sensor's performance in real-world conditions, we tested water samples from different sources: seawater from Skanes Monastir, Tunisia, and local tap water from the laboratory, and colored water obtained from a local shop (Jeans Laboratory, Textile Department). The water samples were filtered to remove

<figure><img src="image_8.png" /><figcaption>**Fig. 7.** Evaluation of (a) long-term stability, (b) intra-electrode reproducibility with regeneration using 2 M EDTA, and (c) inter-electrode reproducibility of the GO@ZnO@SiO₂-modified GCE for the simultaneous detection of Pb²⁺ and Cd²⁺ ions (1 × 10⁻⁵ M) in ABS (0.1 M, pH 5.0).</figcaption></figure>
any particulate matter that could potentially affect the electrochemical measurements. To reduce matrix effects and maintain consistent ionic conditions, the samples were diluted ten-fold using ultrapure water. Subsequently, known concentrations of Pb²⁺ and Cd²⁺ were spiked into the diluted samples, and the sensor's response was measured under optimized conditions (acetate buffer at pH 5 with a 5-minute accumulation time).

For seawater, the recovery rates for Pb²⁺ ranged from 91.12 % to 100 %, while Cd²⁺, the recovery values ranged from 101 % to 104 %,

demonstrating the sensor's accuracy in the presence of salts and other components commonly found in seawater. In tap water, the recoveries for Pb²⁺ ranged from 82.3 % to 99.8 %, and for Cd²⁺, the recovery was between 88.8 % and 95.6 %, both of which are in good agreement with the expected concentrations (Table 2). Colored water, a more complex matrix, yielded recovery rates for Pb²⁺ between 81 % and 97.8 %, and for Cd²⁺, the recovery ranged from 95.2 % to 99.8 %. These recovery rates fall within the generally accepted range of 80-120 % for analytical methods, as suggested by standard guidelines in analytical chemistry (e. g., ICH Q2(R1) and EPA Method 3050B) [75]. This indicates that the sensor performs well in real-world conditions and is capable of accurately detecting Pb²⁺ and Cd²⁺ ions in complex water matrices. All recovery percentages were within the acceptable range, confirming the reliability and effectiveness of the GO@ZnO@SiO₂/GCE sensor for detecting trace levels of Pb²⁺ and Cd²⁺ in environmental water samples. These results underscore the sensor's potential for routine environmental monitoring and water quality assessments.

## 7. Conclusion

In this study, we introduce a novel electrochemical sensor based on a glassy carbon electrode modified with a composite of SiO₂, ZnO, and graphene oxide (GO) for the simultaneous detection of Pb(II) and Cd(II) in environmental water samples. The synergistic combination of SiO₂, ZnO, and GO significantly enhances electron transfer, increases surface area, and improves metal ion binding, making this sensor a promising tool for on-site detection of trace-level toxic metals. Under optimized conditions, this sensor achieved detection limits of 7.5 × 10⁻⁹ M for Pb (II) and 1.25 × 10⁻⁸ M for Cd(II), wide linear ranges, and excellent selectivity, with minimal interference from coexisting ions. Recovery tests on real water samples demonstrated good accuracy, with Pb(II) recoveries ranging from 81 % to 100 % and Cd(II) recoveries between 89 % and 104 %, further highlighting the sensor's practical applicability. The successful application of the sensor to real water samples validates its utility for detecting trace levels of heavy metals, making it a promising tool for environmental monitoring and contamination analysis. Future work will focus on enhancing the selectivity and sensitivity of the sensor through the addition of specific functional groups onto the nanocomposite surface. This approach could improve target ion recognition and broaden the sensor's applicability to other toxic metals or organic pollutants. Further studies may also explore sensor integration into portable detection platforms for rapid, in situ environmental analysis.

### CRediT authorship contribution statement

**Afef Dhaffouli:** Writing - original draft, Methodology, Investigation, Formal analysis. **Younes Moussaoui:** Writing - original draft, Supervision, Methodology. **Pedro A. Salazar-Carballo:** Writing - original draft, Supervision, Methodology, Investigation. **Michael Holzinger:** Supervision, Methodology, Formal analysis. **Soledad Carinelli:** Methodology, Investigation, Formal analysis. **Houcine Barhoumi:** Supervision, Methodology.

### Declaration of competing interest

The authors declare that they have no known competing financial

<table><caption>**Table 2**
Recovery Evaluation of Pb²⁺ and Cd²⁺ in Real Water Samples from Sea water, Tap Water, and Colored Water.</caption><thead><tr><th>Sample</th><th>Added Pb<sup>2+</sup> (M)</th><th>Added Cd<sup>2+</sup> (M)</th><th>Found Pb<sup>2+</sup> (M)</th><th>Found Cd<sup>2+</sup> (M)</th><th>Recovery Pb<sup>2+</sup> (%)</th><th>Recovery Cd<sup>2+</sup> (%)</th></tr></thead><tbody><tr><td>Sea</td><td>1.00 ×</td><td>2.50 ×</td><td>9.12 ×</td><td>2.53 ×</td><td>91.2</td><td>101</td></tr><tr><td rowspan="3">Water</td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-8</sup></td><td>10<sup>-7</sup></td><td rowspan="3">100</td><td rowspan="3">104</td></tr><tr><td>5.00 ×</td><td>5.00 ×</td><td>5.01 ×</td><td>5.21 ×</td></tr><tr><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td></tr><tr><td rowspan="3">Tap Water</td><td>1.00 ×</td><td>2.50 ×</td><td>8.23 ×</td><td>2.22 ×</td><td>82.3</td><td>88.8</td></tr><tr><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-8</sup></td><td>10<sup>-7</sup></td><td rowspan="2">99.8</td><td rowspan="2">95.6</td></tr><tr><td>5.00 ×</td><td>5.00 ×</td><td>4.99 ×</td><td>4.78 ×</td></tr><tr><td>Colored Water</td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>81</td><td>95.2</td></tr><tr><td></td><td>1.00 ×</td><td>2.50 ×</td><td>8.10 ×</td><td>2.37 ×</td><td>97.8</td><td>99.8</td></tr><tr><td></td><td><sup>56</sup><sub>10</sub>(R0) ×</td><td><sup>56</sup><sub>10</sub>(R0) ×</td><td><sup>46</sup><sub>10</sub>(R0) ×</td><td><sup>46</sup><sub>10</sub>(R0) ×</td><td></td><td></td></tr><tr><td></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td>10<sup>-7</sup></td><td></td><td></td></tr></tbody></table>

interests or personal relationships that could have appeared to influence the work reported in this paper.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.inoche.2025.114871.

### Data availability

The data that has been used is confidential.

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